Báo cáo khoa học: Characterization of the serotoninergic system in the C57BL/6 mouse skin potx

Characterization of the serotoninergic system in the C57BL/6
mouse skin
Andrzej Slominski
1
, Alexander Pisarchik
1
, Igor Semak
2
, Trevor Sweatman
3
and Jacobo Wortsman
4
1
Department of Pathology, University of Tennessee Health Science Center, Memphis, TN, USA;
2
Department of Biochemistry,
Belarus State University, Minsk, Belarus;
3
Pharmacology, University of Tennessee Health Science Center, Memphis, TN, USA;
4
Department of Internal Medicine, Southern Illinois University, Springfield, IL, USA
We showed expression of the tryptophan hydroxylase gene
and of tryptophan hydroxylase protein immunoreactivity in
mouse skin and skin cells. Extracts from skin and melano-
cyte samples acetylated serotonin to N-acetylserotonin and
tryptamine to N-acetyltryptamine. A different enzyme from
arylalkylamine N-acetyltransferase mediated this reaction,
as this gene was defective in the C57BL6 mouse, coding
predominantly for a protein without enzymatic activity.
Serotonin (but not tryptamine) acetylation varied according
to hair cycle phase and anatomic location. Serotonin was

also metabolized to 5-hydroxytryptophol and 5-hydroxy-
indole acetic acid, probably through stepwise transform-
ation catalyzed by monoamine oxidase, aldehyde
dehydrogenase and aldehyde reductase. Activity of the
melatonin-forming enzyme hydroxyindole-O-methyltrans-
ferase was notably below detectable levels in all samples of
mouse corporal skin, although it was detectable at low levels
in the ears and in Cloudman melanoma (derived from the
DBA/2 J mouse strain). In conclusion, mouse skin has the
molecular and biochemical apparatus necessary to produce
and metabolize serotonin and N-acetylserotonin, and its
activity is determined by topography, physiological status of
the skin, cell type and mouse strain.
Keywords: mouse skin; serotonin acetylation; arylalkylamine
N-acetyltransferase; tryptophan hydroxylase; hair cycle.
The skin is the largest body organ and functions as a
metabolically active biological barrier regulating internal
homeostasis and separating the internal milieu from
noxious environmental factors [1]. These functions are
mediated by the skin immune, pigmentary, neuroendo-
crine, adnexal and vascular systems [1–7]. Most recently
we have uncovered local serotoninergic and melatoniner-
gic systems as novel elements of the cutaneous neuro-
endocrine components of human and hamster skin [8–12].
Serotonin is the product of a multistep metabolic pathway
that starts with the hydroxylation of the aromatic
aminoacid
L
-tryptophan by tryptophan hydroxylase
(TPH) [13,14]. Serotonin can be acetylated by arylalkyl-

amine N-acetyltransferase (AANAT) to N-acetylserotonin
(NAS),whichisfurthertransformedtomelatoninby
hydroxyindole-O-methyltransferase (HIOMT) [13,15].
Serotonin can act as a neurohormone, regulator of
vascular tone, immunomodulator and growth factor,
while melatonin can act as a hormone, neurotransmitter,
cytokine or biological modifier [2,15–17]. Some of these
functions may be pertinent to skin physiology, which
exhibits basic differences among the mammalian species.
In rodents (mostly nocturnal animals) the skin is shielded
from the damaging effect of solar radiation by fur [18],
and the morphology of the entire mouse skin changes in
close coordination with the cyclic activity of the hair
follicle [19]. Mouse hair follicle cycling is characterized by
a precisely regulated, time frame-restricted and differential
pattern in the expression and activity of melanogenesis
related proteins, PH, pterins and thioredoxin reductase
[20]. Hair cycle-dependent changes also involve adrenergic
innervation and specific patterns of b2-adrenergic receptor
expression [21].
Our previous studies raised the possibility that the level
of activity of an endogenous serotoninergic pathway would
specifically determine whether its products are for internal
use (intracrine regulation), or for external secretion (para-
or autocrine regulation). Because mouse skin differs from
human skin, we anticipated interspecies heterogeneity in
the cutaneous expression of elements of the serotoninergic
pathway. Therefore, we have tested the expression of dif-
ferent elements of the serotoninergic system in the C57BL/
6 mouse and related their activity in the skin to the

phase of the hair cycle and to the cutaneous cellular
compartments.
Correspondence to A. T. Slominski, Department of Pathology,
University of Tennessee Health Science Center, 930 Madison Ave
Rm 519, Memphis, TN, USA.
Fax: + 1 901 448 6979, Tel.: + 1 901 448 3741,
E-mail:
Abbreviations: TPH, tryptophan hydroxylase; AANAT, arylalkyl-
amine N-acetyltransferase; NAS, N-acetylserotonin; HIOMT,
hydroxyindole-O-methyltransferase; PH, phenylalanine hydroxylase;
CDL, curved desolvation line; TBST, Tris buffered saline with Tween
20; NAT, arylamine N-acetyltransferase; Bis, bisubstrate analog
coenzyme A-S-acetyltryptamine; MAO, monoamine oxidase;
5HIAA, 5-hydroxyindolacetic acid; 5HTPOL, 5-hydroxytryptophol.
Note: a website is available at />(Received 30 April 2003, revised 4 June 2003, accepted 9 June 2003)
Eur. J. Biochem. 270, 3335–3344 (2003) Ó FEBS 2003 doi:10.1046/j.1432-1033.2003.03708.x
Experimental procedures
Tissue
Murine samples consisted of skin isolated at telogen and
anagen stages of the hair cycle as described previously, and of
brain, pituitary and spleen tissues [12,19]. Experiments
performedintheUSAusedC57BL/6strainfemalemice
(8 weeks old) purchased from Taconic (NY) and housed in
community cages at the animal facilities of the Albany
MedicalCollege,Albany,NY.LC/MSassays,performedin
Belarus, also used C57BL/6 mice (males 18 weeks old)
obtained from the Vivarium of the Department of Bio-
testings of the Institute of Bioorganic Chemistry (Belarus
State University, Minsk, Belarus). The animals were housed
in a temperature-controlled room on a 12-h light : 12-h dark

schedule (lights turned on at 06.00 h) with food and water
available ad libitum. The animals were killed under pento-
barbital anesthesia and selected organs as well as back skin
were collected following protocols routinely used in our
laboratory, and then stored at )80 °C until use [12,19]. The
Institutional Animal Care and Use Committee at Albany
Medical College approved the original experimental proto-
col, and a similar protocol for mice was approved at
University of Tennessee Health Science Center. Approval for
the experiments performed in Minsk, Belarus was granted by
the Belarus University Animal Care and Use Committee.
Cell culture
Tested cell lines comprised mouse Cloudman S91 (sublines
6 and M3) and hamster AbC-1 melanoma cells, and mouse
immortalized normal melanocytes (MelA). Melanoma cells
were grown in Ham’s F10 medium as described previously,
and the media were supplemented with 10% (v/v) fetal
bovine serum and 1% antibiotic/antimycotic mixture
(Gibco) [22]. MelA (the gift of D. Bennett, St George’s
Hospital, London, UK), was cultured in RPMI 1640 media,
supplemented with 10% (v/v) 200 n
M
bovine serum
(phorbol-12-myristate-13-acetate), in the presence of 10%
(v/v) CO
2
. After washing with NaCl/P
i
, melanoma cells
were detached using Ca- and Mg-free Tyrode’s solution,

containing 1 m
M
EDTA, while normal immortalized mouse
melanocytes were trypsinized. The cells were centrifuged
then frozen at )80
o
C, for use in further analyses.
Enzymatic assays
Arylakylamine/arylamine N-acetyl transferase acti-
vity. N-acetyl transferase activity was measured either by
the method of Thomas et al. [23], using a modified
RP-HPLC separation with fluorimetric detection of the
reaction products [24] or by direct LC/MS detection of
metabolic intermediates [8]. For both methods, tissue or cell
samples were homogenized in an ice-cold 0.25
M
potassium
phosphate buffer (pH 6.8) containing 1 m
M
dithiothreitol,
1m
M
EGTA and protease inhibitor cocktail (2 lLÆmL
)1
homogenization mixture, Sigma). Homogenates were cen-
trifuged at 15 000 g for 10 min at 4 °C. Supernatants were
used to measure serotonin N-acetyl transferase in the
presence of 1 m
M
serotonin or tryptamine and 0.5 m

M
of
acetyl coenzyme A in 0.25
M
potassium phosphate buffer
(pH 6.8) for 1 h or 1.5 h (when indicated) at 37 °C. The
enzymatic reaction was stopped by the addition of HClO
4
.
After centrifugation, the supernatant was subjected to
HPLC in a system equipped with a Novapak C
18
reverse-
phase column (100 · 5 mm, 4 lm particle size; 60 A
˚
pore
size) and a fluorometric detector with excitation and
emission wavelengths set at 285 and 360 nm, respectively.
The elution was carried out isocratically at ambient
temperature with a flow rate of 1.5 mLÆmin
)1
for the
mobile phases chosen according to the amine substrate to be
used. The mobile phase contained 4 m
M
sodium 1-octane-
sulfonate as an ion-pairing agent, 50 m
M
ammonium
formate (pH 4.0) vs. methanol (80 : 20, v/v) for serotonin

and (75 : 25, v/v) for tryptamine. Elution peaks of
N-acetylserotonin and N-acetyltryptamine were verified by
coelution with the authentic standards. The peak areas
were quantified in relation to known concentrations of
N-acetylserotonin and N-acetyltryptamine standards. Back-
ground controls consisted of the reaction mixture incubated
without substrate or enzyme source.
For LC/MS analysis, the final concentrations of acetyl
CoA and serotonin in reaction mixtures were 0.5 m
M
and
5m
M
, respectively. Aliquots of the final reaction super-
natants (see above) were separated on an LCMS-QP8000a
(Shimadzu, Japan) through Restec Allure C18 reverse-phase
column (150 · 4.6 mm; 5 lm particle size; 60 A
˚
pore size).
The elution was carried out isocratically at a flow rate of
0.3 mLÆmin
)1
at 30 °C by mobile phases consisting of 20%
(v/v) methanol and 0.1% (v/v) acetic acid. The effluent from
the HPLC system was routed to the MS electrospray
interface used in the positive mode. Nitrogen was used as
nebulizing gas. MS parameters were as follows: nebulizer gas
flow rate was 4.5 LÆmin
)1
; the electrospray voltage was

4.5 kV; CDL heater temperature was 250 °C. Selected
ion monitoring mode was applied to detect ions with
m/z ¼ 219. The LC/MS workstation
CLASS
-8000 software
was used for system control and data acquisition (Shimadzu,
Japan). Quantitative determination of N-acetylserotonin
was made by comparing the observed peak areas with the
peak areas of known concentrations of the NAS standard.
Hydroxyindole-O-methyl-transferase activity. Hydroxy-
indole-O-methyl-transferase activity was assayed as des-
cribed previously [24]. Briefly, tissue homogenates were
centrifuged at 15 000 g for 10 min at 4 °C. Supernatants
were used to measure enzymatic activity in the presence of
0.5 m
M
of S-adenosyl-
L
-methionine and 1 m
M
of N-acetyl-
serotonin in 0.05
M
sodium phosphate buffer (pH 7.9).
After incubation for 1 h at 37 °C, the enzymatic reaction
was stopped by the addition of HClO
4
and, after centri-
fugation, the supernatants were subjected to HPLC in the
system described above for measurement of acetyl trans-

ferase activity, with tryptamine as the substrate. Compar-
ison with the retention times of the authentic standards
identified elution peaks for N-acetylserotonin and melato-
nin. Protein concentration was determined with a dye-
binding method using BSA as the standard [24].
Western blot analysis
Cultured cells were detached in Tyrode’s solution plus 1 m
M
EDTA, centrifuged at 200 g for 10 min at 4 °C and the cell
3336 A. Slominski et al.(Eur. J. Biochem. 270) Ó FEBS 2003
pellets were then washed with NaCl/P
i
and frozen at
)70 °C. For protein isolation, frozen cell pellets or skin
samples were homogenized with a glass homogenizer in
ice-cold buffer A containing 20 m
M
Tris, pH 7.5, 5 m
M
EDTA, 120 lgÆmL
)1
leupeptin, 3 l
M
pepstatin and 3 m
M
amino-ethylbenzene sulfonyl fluoride. The homogenates
were centrifuged at 16 000 g for 10 min at 4 °Ctoremove
cell debris and centrifuged at 100 000 g for 1 h at 4 °C. The
supernatants representing the cytosol fraction were removed
and stored at )80 °C for further analysis. Separate aliquots

of 5 lL were used for protein determination using the
Micro Protein Kit (Sigma). Fifty micrograms of protein
were separated on a 12% (w/v) SDS polyacrylamide gel,
transferred to immobilion-P poly(vinylidene difluoride)
membrane (Millipore Corp, Bedford, MA, USA) and
nonspecific binding sites were blocked by incubation in
5% (w/v) nonfat powdered milk in TBST (50 m
M
Tris,
pH 7.5, 150 m
M
NaCl, 0.01% Tween 20) for 4 h at room
temperature. Immunodetection of the TPH or AANAT
proteins was performed after overnight incubation with
polyclonal rabbit anti-human TPH (dilution 1 : 1000, at
4 °C) as the primary antibody (Chemicon, Temecula, CA)
or with rabbit anti-(rat AANAT
25-200
) serum (dilution
1 : 10 000, room temperature; gift of D. Klein, NIH,
Bethesda, MD, USA). In parallel incubation we used
preimmune rabbit serum at the same dilution as the
corresponding antiserum (gift of D. Klein, NIH). The
following day membranes were washed twice in TBST for
10 min. Goat anti-rabbit IgG coupled to horseradish
peroxidase was used as a secondary antibody (dilution
1 : 4000, 1 h) (Santa Cruz Biotechnology). Membranes
were washed twice in TBST and once in TBS. Bands were
visualized using ECL reagent (Amersham Pharmacia Bio-
tech) according to the manufacturer’s instructions.

RNA extraction and cDNA preparation
Tissues were pulverized in liquid nitrogen using a mortar
and then suspended in Trizol (Invitrogen) and the isolation
of RNA followed the manufacture’s protocol. The synthesis
of first-strand cDNA was performed using the Superscript
preamplification system (Invitrogen). Total RNA (5 lgper
reaction) was reverse transcribed according to the manu-
facturer’s protocol, using oligo(dT) as the primer.
All samples were standardized for analysis by the
amplification of housekeeping gene GAPDH as described
previously [25]. Mouse TPH was amplified by a single PCR,
while serotonin AANAT was amplified by nested PCR. The
localization of the primers in corresponding genes is
presented in Figs 1A and 3A. The reaction mixture
(25 lL) contained 2.5 m
M
MgCl
2
,0.25
M
of each dNTP,
0.4 l
M
of each primer, 75 m
M
Tris/HCl (pH 8.8), 20 m
M
(NH
4
)

2
SO
4
, 0.01% Tween 20 and 1.25 U of Taq DNA
polymerase (Promega). The mixture was heated to 94 °Cfor
2.5minandthenamplifiedfor35or30cyclesasspecified:
94 °C for 30 s (denaturation), 60 °C for 45 s (annealing) and
72 °C for 1 min (extension).
TPH was amplified by a single PCR using primers P108
(5¢-CTTTCGAGTCTTTCACTGCACTC-3¢) and P109
(5¢-CATTCATGGCACTAGTTATGCTC-3¢). Exons 1–2
of mouse AANAT were amplified by primers P242
(5¢-CCAGCGAGTTCCGTTGCCTTAC-3¢) and P243
(5¢-GCCTGTGCAGTGTCAGTGACTC-3¢) in the first
round and primers P244 (5¢-CGTGTTTGAGATTGAGC
GTGAAG-3¢) and P245 (5¢-CTTGTCCCAAAGTGAGC
CGATG-3¢) in the second round of PCR. Primers for the
first PCR of exons 3–4 of mouse AANAT were P145
(5¢-ACTTGGATGAGATCCGGCACTTCC-3¢) and P148
(5¢-GGCTGACTGCCCAGGTGGTGAAG-3¢). Primers
for the second round were P146 (5¢-GTCCAGAGCTGT
CACTGGGC-3¢)andP147(5¢-AGGACAGAGCCCT
TGCCCTGCTG-3¢). Annealing temperature for the ampli-
fication of exons 3 and 4 was 67 °C.
Amplification products were separated by agarose gel
electrophoresis and visualized by ethidium bromide staining
according to the standard protocol used in our laboratory
[8,24,25]. The identified PCR products were excised from
the gel and purified by GFX PCR DNA using the gel band
purification kit (Amersham-Pharmacia-Biotech). PCR frag-

ments were cloned in pGEM-T easy vector system (Pro-
mega) and purified by plasmid purification kit (Qiagen).
Sequencing was performed in the Molecular Resource
Center at the University of Tennessee HSC (Memphis)
using an Applied Biosystems 3100 Genetic Analyzer and the
BigDye
TM
Terminator Kit.
Results
Tryptophan hydroxylase expression
Using mouse-specific primers for mouse tryptophan
hydroxylase (Fig. 1A) we subjected RNA from different
tissues and cell lines to RT-PCR. The amplified fragments
of 530 bp were sequenced and shown to have complete
(100%) homology with the corresponding gene fragment.
Thus, the tryptophan hydroxylase gene was expressed in the
brain, pituitary, spleen, Cloudman S91 melanoma cells,
MelA immortalized normal melanocytes, and anagen and
catagen skin (growing and involutional phases of the hair
cycle, respectively). The TPH gene was either absent (two
experiments) or present (one experiment) in telogen (resting
phase of the hair cycle) (Fig. 1B, Table 1).
Western blot analysis using two different antibodies was
performed in cytoplasmic extracts from mouse skin, MelA
Fig. 1. TPH mRNA expression in murine tissues and skin cell lines.
(A) Localization of the primers to the TPH coding exons. The numbers
correspond to protein coding exons revealed after comparison of
mRNA (NM-009414) and genomic DNA. (B) Expression of a 530 bp
TPH transcript in brain (2), anagen IV (3), anagen V (4), middle
anagen VI (5), late anagen VI (6), and telogen skin (7), spleen (8),

subline 6 of S91 melanoma (9) and subline M3 of S91 melanoma (10).
DNA markers are shown in lanes 1 and 11.
Ó FEBS 2003 Serotoninergic system in mouse skin (Eur. J. Biochem. 270) 3337
immortalized normal melanocytes, S91 (clone 6) mouse
melanoma cells and pig pineal gland control. These tests
identified a specific protein of 53–55 kDa precipitated by
anti-TPH Igs (Fig. 2; arrow). Additional proteins of both
higher (83–85 kDa) and lower molecular mass were also
detected by the same antibodies (Fig. 2).
AANAT gene expression
Using different pairs of specific primers located at exons 1
and 2, and 3 and 4 of the AANAT gene we subjected RNA
from mouse tissue and normal and malignant melanocytes
to RT-PCR amplification (Fig. 3A). RT-PCR with primers
located at exons 1 and 2 demonstrated the presence of a
163 bp fragment in all tissues and cells tested; this fragment
showed 100% homology with the corresponding fragment
of mouse AANAT cDNA (Fig. 3B). In addition, an
aberrantly spliced isoform of 252 bp was detected in the
brain, pituitary, spleen and M3 subline of S91 melanoma,
but not in the C57BL/6 mouse skin or the MelA melano-
cytes (Fig. 3B, Table 1). This isoform had the insertion of
89 bp from an intron leading to a frame shift after the first
exon. Translation of this transcript would produce a protein
of 59 amino acids with a molecular mass of 6.5 kDa, devoid
of enzymatic activity. Tests performed with primers located
at exons 3 and 4 of the AANAT gene yielded bands of
187 bp, 289 bp and 118 bp (Fig. 2A,C, Table 1). The
187 bp band corresponding to the normal AANAT cDNA
was detected in the brain, pituitary, parental subline M3 of

Cloudman S91 melanoma and anagen IV mouse skin. It
was not detected in skin at telogen, anagen V, early and late
anagen VI and catagen phases of the hair cycle (Fig. 2C,
Table 1). The 289 bp band represented the aberrantly
spliced isoform described previously by Roseboom et al.
[26] with the insertion of a 102 bp fragment that produced a
frame shift; translation of this mRNA should generate an
inactive enzyme [26]. It was detected as the predominant
AANAT species in brain, pituitary and anagen IV skin of
the C57BL/6 mouse, but only as a minor component in
Cloudman S91 melanoma (Fig. 2C, Table 1). The 118 bp
band was detected only in the spleen, and had a deletion of
69bp(24bpfromexon3and45bpfromexon4)buta
preserved reading frame. Thus, this transcript would
produce a protein with a deletion of 23 amino acids and
an apparent molecular mass of 20.4 kDa. It is, however,
unclear whether this protein posses enzymatic activity. As
the deleted fragment does not include any of the residues
critical for substrate binding or enzymatic activity, it is
highly probable that it may be enzymatically active.
Western blot analysis showed a protein with the expec-
ted size for AANAT (24 kDa) immunoprecipitated by
Table 1. Tissue and cell line expression pattern of TPH and AANAT
genes from mouse source. Numbers 118 (GenBank Accession Number
AY131261), 163 (GenBank Accession Number AF004108), 252
(GenBank Accession Number AY131262), 187 (GenBank Accession
Number AF004108) and 289 (GenBank Accession Number
AF004111) represent the size of corresponding transcripts (bp) detec-
ted by RT-PCR.
Specimens TPH

AANAT
Exons 1 and 2
AANAT
Exons 3 and 4
Brain (+) 163, 252 187, 289
Pituitary (+) 163, 252 187, 289
Skin (anagen IV) (+) 163 (–)187, 289
Skin (anagen V) (+) 163 (–)
Skin (middle anagen VI) (+) 163 (–)
Skin (late anagen VI) (+) 163 (–)
Skin (telogen) (–)(–)(+) 163 (–)
Spleen (+) 163 118
Melanoma S91
(subline M3)
(+) 163, 252 187, 289
MelA melanocytes (+) 163 (–)
Fig. 2. Detection of TPH immunoreactive proteins in mouse skin and
cultured melanocytes and melanoma cells. (A) Immunoprecipitation
using rabbit anti-TPH Igs: skin at catagen (1), anagen III (2) and
anagen V (3) phases of hair growth, MelA melanocytes (4), Cloudman
S91 melanoma (5), pig epiphysis (6). The arrow indicates a TPH-like
immunoreactivity of 53 kDa. (B) Immunoprecipitation using sheep
anti-TPH Igs. Molecular masses in kDa are indicated on the left; skin
at telogen (1), anagen III (2), catagen (3) phases of hair growth, MelA
melanocytes (4). The arrow indicates a TPH-like immunoreactivity of
53 kDa. (C) Immunoprecipitation control for B. The panel presents
the blot incubated with secondary antibody only. Explanation of
numbersandarrowisasabove(B).
3338 A. Slominski et al.(Eur. J. Biochem. 270) Ó FEBS 2003
anti-(rat AANAT) serum (anti-rAANAT25-200) in control

rat brain, Cloudman S91 and hamster AbC-1 melanomas
but not in the mouse skin (Fig. 4). Detection of this
AANAT-like immunoreactivity appeared to represent true
expression, as it was not seen in control membranes
incubated with preimmune serum.
Acetylation of serotonin and tryptamine
by skin extracts
Using the RP-HPLC system with fluorimetric detection or
LC/MSwewereabletofirmlyestablishthatextractsof
C57BL/6 mouse skin and of cultured normal and malignant
melanocytes after addition of acetyl-CoA transformed
serotonin to N-acetylserotonin (Figs 5 and 6, Tables 2
and 3). In contrast, the acetylation of tryptamine by skin
extracts was less efficient (Table 2).
The experiments with LC/MS confirm NAS identity by
showing the appearance of an adduct ion (M + H)
+
at
m/z ¼ 219 with the same retention time as the correspond-
ing NAS standard, e.g. m/z ¼ 219 (calculated mass ¼
218 Da) at a retention time of 27 min (Fig. 6B). Kinetic
analysis of N-acetylase activity showed K
m
and V
max
values
of 0.56 m
M
and 174 pmolÆh
)1

for serotonin substrate,
respectively (Fig. 7). We also tested the effect of bisubstrate
analog coenzyme A-S-acetyltryptamine (Bis; a specific
inhibitor of arylalkylamine activity) on the enzymatic
Fig. 4. AANAT-like immunoreactivity is absent in C57BL/6 mouse skin
and present in hamster AbC-1 and mouse S91 Cloudman melanomas.
Immunoprecipitation using rabbit anti-AANAT Igs (upper panel).
Lower panel presents blots incubated with secondary antibody only.
Markers in kDa are shown on the left; rat brain (1), hamster AbC-1
melanoma (2), mouse S91 Cloudman melanomas (3), C57BL/6 mouse
skin at anagen III (4), anagen V (5) and catagen (6) phases of hair
growth. Arrow indicates AANAT-like immunoreactivity of 24 kDa.
Fig. 5. HPLC chromatogram obtained from reaction mixture in which
S-91 melanoma cells were used as the enzyme source. Experimental
incubation with acetyl CoA and serotonin (A) or tryptamine (B) and
corresponding control extracts without amine substrate (C and D).
N-acetylserotonin or N-acetyltryptamine indicate the elution position
of corresponding standards.
Fig. 3. AANAT mRNA expression in murine tissues and cell lines.
Structure of the murine AANAT gene. Open boxes represent exons.
Shadowed and black boxes are fragments of coding sequence located
after the frame shift and cryptic exons, respectively. Primers are shown
by arrows. (B) Detection of 163 and 252 bp AANAT PCR bands
amplified by primers located at exons 1 and 2. DNA ladder (1, 14),
pituitary (2), brain (3), MelA melanocytes (4), M3 subline of S91 mel-
anoma (5), anagen IV (6), anagen V (7), early anagen VI (8), middle
anagen VI (9), late anagen VI (10), and telogen (11) skin; #6 subline of
S91 melanoma (12); telogen stain (13). (C) Expression of 187 and
289 bp AANAT transcripts amplified by primers located at exons 3
and 4. DNA ladder (1), brain (2), pituitary (3), M3 subline of S91 mel-

anoma (4), anagen IV (5); late anagen VI (6), telogen skin (7), spleen (8).
Ó FEBS 2003 Serotoninergic system in mouse skin (Eur. J. Biochem. 270) 3339
activity in skin extracts at a concentration of < 1 l
M
,and
found that it inhibited serotonin N-acetyltransferase activity
by approximately 65%, with minimal additional effects at
concentrations > 1 l
M
(Fig. 6C,D).
Serotonin N-acetylase activity was dependent on the
phase of the hair cycle being low in telogen skin, increasing
during anagen to a peak at late anagen VI and decreasing
during catagen (Table 2). The enzymatic activity towards
tryptamine did not show clear hair cycle dependence. Thus,
the ratio between enzymatic activity toward tryptamine and
serotonin changed during hair cycling from approximately
4intelogenandanagenIIIto16and17inmiddleandlate
anagen VI, being 14 in catagen. The same ratio was 1.5 in
the ear and 1 in S91 melanoma cells (Table 3). While testing
cultured cells, we noted significantly lower enzymatic
activity in preparations of frozen cells as compared to fresh
cells (data not shown).
Serotonin and NAS metabolism in mouse skin
LC/MS analysis of the reaction products of arylalkylamine/
arylamine activity in mouse corporal skin showed two
metabolites with retention times of 19 min and 23.5 min,
corresponding to 5-hydroxytryptophol (5HTPOL; m/z of
178 [M + H]
+

, calculated mass ¼ 177 Da) and 5-hydroxy-
indolacetic acid (5HIAA; m/z of 198 [M + H]
+
,calcula-
ted mass ¼ 197 Da) (Fig. 8). Accumulation of both
compounds was inhibited by the monoamine oxidase
inhibitor pargyline (Fig. 8).
HIOMT activity was below the level of detectability in
corporal back skin at telogen, anagen VI and catagen
phases of the hair cycle (not shown). However, the
chromatograms of products from the HIOMT assay did
show nine additional fluorescent products, apart from the
NAS substrate. The pattern of expression of these products
changed during progression of the hair cycle (Fig. 9).
RP-HPLC separation of the reaction products of the
HIOMT assay from mouse ear and Cloudman S91 mouse
melanoma cells showed weak but detectable transformation
of NAS to a species with a retention time identical to
melatonin (Fig. 10). These results suggest that both Cloud-
man melanoma cells (derived from the DBA 12J mouse)
and the ears of the C57BL/6 mouse express HIOMT
activity, albeit at low levels. The same activity, however, is
undetectable in the corporal skin of the C57BL/6 mouse.
Discussion
The current study demonstrates that mouse skin and skin
cells have the molecular and biochemical apparatus neces-
sary to produce and metabolize serotonin and N-acetyl-
serotonin. Activity of this serotoninergic system varied
depending on anatomical location, phase of hair cycle and
skin cell type.

In this study, we show the specific expression of the
tryptophan hydroxylase gene in normal and malignant
mouse melanocytes, in anagen and catagen skin, and in
pituitary and spleen. In telogen skin gene expression was
low. Expression of the TPH gene in skin and in skin-derived
normal and malignant melanocytes was accompanied by
detection of TPH immunoreactive protein with its expected
molecular mass of 53–55 kDa. The molecular mass of newly
translated TPH is 51 kDa and it increases to 53–60 kDa
after post-translational modification [14,27]. Variants of
higher and lower molecular mass have also been described
and are believed to represent products of enzyme turnover
Fig. 6. LC/MS analysis of serotonin transformation to NAS by mouse
skin. Control reaction mixture (A) contains only substrates and
cofactors without addition of the extract. Experimental incubation
enzyme extracts, acetyl CoA and serotonin without (B) or with (C)
1 l
M
of Bis. The arrow identifies m/z ¼ 219 at a retention time of
26 min, corresponding to the NAS product. The dose-dependent effect
of Bis on serotonin N-acetyltransferase activity is shown in (D).
3340 A. Slominski et al.(Eur. J. Biochem. 270) Ó FEBS 2003
[28,29]. In mastocytoma cells, ubiquitination of TPH can
generate species of higher molecular mass (80–93 kDa) as
intermediates in a very fast turnover process driven by
proteasomes, that leads to the final degradation of native
TPH to species of lower molecular mass [28,29]. Such
turnover process would be consistent with our detection of
TPH immunoreactive species with the expected relative
molecular mass (53–55 kDa) as well as species of both

higher and lower relative molecular mass. Thus, the high
molecular mass TPH-like species may represent ubiquiti-
nated TPH, whereas the low molecular mass TPH-like
species could represent degradation products. However, as
alternative splicing has already been reported for the TPH
gene [30,31], the possibility that part of the diversity in
TPH-like immunoreactivity molecular mass may be due to
translation of alternatively spliced TPH mRNAs cannot be
totally excluded. The observed expression of the TPH gene
in spleen and pituitary deserves further study to assess the
possible production of serotonin by these organs.
Our extensive molecular analyses of AANAT transcripts
in the C57BL/6 mouse demonstrate genetic defects that
result in the predominant transcription of aberrant isoforms
encoding protein(s) without enzymatic activities (Table 1).
Thus, our data support the conclusion of Roseboom et al.
[26] that this species is a natural ÔknockdownÕ for the
AANAT. However, because we document separately the
capability of C57BL/6 mouse skin to acetylate serotonin
and tryptamine, the above reactions are likely to be
catalyzed by arylamine N-acetyltransferase (NAT). NAT
is a cytosolic enzyme that acetylates nitrogen or oxygen
atoms of aromatic amines, hydrazines and N-hydroxyl-
amines, thus playing an important detoxifying role [32–35].
There are two isozymic forms of the enzyme, NAT-1 and
NAT-2, encoded by different genetic loci. Each isoform has
at least 15 different allelic forms. Expression of NAT-1
cDNA in mammalian or bacterial cells has demonstrated
that the enzyme is capable of acetylating both endogenously
derived arylalkylamines and exogenous arylamines. NAT-1

is ubiquitously expressed in different tissues including the
skin, and expression of the NAT-1 gene has been demon-
strated by in situ hybridization in rat skin [36–38]. Therefore,
we suggest that serotonin and tryptamine acetylation by
skin extracts of the C57BL/6 mouse is probably mediated by
one of the allelic forms of NAT-1.
Testing for the effect of Bis uncovered a dual action in the
cutaneous acetylation process, e.g. significant inhibition
at concentrations equal to or below 1 l
M
, indicative of
selectivity towards arylalkylamines [39], and insensitivity to
Table 2. Hair cycle dependent changes in skin serotonin acetyl trans-
ferase activity. Values represent means ± SEM of two to three assays.
Mouse skin
Enzyme Activity
pmolÆmin
)1
Æmg protein
)1
(Mean ± SEM)
Activity Ratio
(serotonin/
tryptamine)
Serotonin Tryptamine
Telogen 3.4 ± 0.33 0.91 ± 0.001 4
Anagen III 5.64 ± 0.55 1.57 ± 0.2 4
Anagen IV 10.52 ± 0.27 1.02 ± 0.05 10
Early anagen VI 12.48 ± 1.3 0.78 ± 0.09 16
Late anagen VI 16.75 ± 2.46 1.0 ± 0.03 17

Catagen 12.68 ± 0.16 0.91 ± 0.001 14
Ears 9.65 ± 0.51 6.1 ± 1.02 1.5
Table 3. Enzymatic activity in normal and malignant melanocytes.
Values represent means ± SEM of two to three assays. bd, below
detectability; na, not applicable.
Cell line
Enzyme Activity
pmolÆmin
)1
Æmg protein
)1
(Mean ± SEM)
Activity
Ratio
(serotonin/
tryptamine)Serotonin Tryptamine
S91 melanoma (6) 1.3 ± 0.01 1.02 ± 0.09 1
MelA melanocytes 2.2 ± 0.48 bd na
S91 melanoma (M3) 15.32 ± 0.001 18.6 ± 1.09 1
Fig. 7. Michaelis–Menten and Lineweaver–Burk (insert) plots of
N-acetyltransferase activity for serotonin in mouse skin.
Fig. 8. LC/MS of products of reaction mixture in which skin extract
was incubated with acetyl CoA and serotonin. 5-Hydroxytryptophol
(arrow pointing to m/z ¼ 178 with a retention time of 20.2 min) was
identified in the reaction mixture (A) and its accumulation was
inhibited by pargyline (B). HIAA (arrow pointing at m/z ¼ 192 with a
retention time of 25 min) was identified in the reaction mixture (C) and
its accumulation was inhibited by pargyline (D).
Ó FEBS 2003 Serotoninergic system in mouse skin (Eur. J. Biochem. 270) 3341
Bis > 1 l

M
(less than 25% decrease in activity), suggestive
of preferential activity towards arylamines [40]. These
results indicate that transformation of serotonin to NAS
in mouse skin extract is mediated by enzymatic activities
different from AANAT. Nevertheless, in at least the DBA/
2 J mouse strain (S91 melanoma), the reaction could still be
mediated by AANAT. Thus, that cell type expressed both
the correct AANAT transcript and the protein with the
expected molecular mass. Therefore, we suggest that
serotonin acetylation is an intrinsic property of rodent skin;
moreover depending on species [41] or specific strains the
reaction can either be mediated by NAT-1 or AANAT, or
by both NAT-1 and AANAT.
The C57BL/6 mouse strain has undetectable production
of melatonin in the pineal gland, and very low-to-undetect-
able concentrations in plasma [42]. This is in agreement with
the genetic defect in AANAT that led Roseboom et al.[26]
to postulate this mouse species as a natural melatonin
ÔknockdownÕ. It must nevertheless be noted that significant
production of melatonin has been reported in peripheral
organs of the same species, most notably in bone marrow-
derived cells [43,44]. Our own studies that document the skin
capability to produce NAS raise the possibility of alternative
AANAT-independent pathways to produce this obligatory
precursor to melatonin in peripheral organs. While our
enzymatic studies excluded corporal skin of the C57BL/6
mouse as a site of melatonin production, we did detect low
HIOMT activity in mouse ears and in S91 melanoma cells.
Thus, we tentatively agree with the notion that mice may

produce melatonin at selected extracranial sites [43,44].
Serotonin is a potent biological agent, and as such needs
tight regulation at the tissue level [16,17], provided by
monoamine oxidase (MAO) pathways. MAO deaminates
serotonin to 5-hydroxyindoleacetaldehyde, which is further
oxidized to 5HIAA by aldehyde dehydrogenase or reduced
to 5-HTPOL by aldehyde reductase [13]. Indeed, when
serotonin was incubated with skin extracts, 5HIAA and
5-HTPOL were readily detected by LCMS, whereas addi-
tion of the MAO inhibitor, pargyline, blocked production
of these compounds. This indicates that serotonin degrada-
tion in the skin includes its oxidative deamination. The
H
2
O
2
produced during this reaction may also be used for
the oxidation of serotonin and other indoleamines, similar
to the intestinal metabolism of tyramine [45].
NAS metabolism was extensive and hair cycle-dependent
in mouse back skin, producing several as yet unidentified
Fig. 9. HPLC chromatograms of products of HIOMT assays in telogen
(A), anagen VI (B) and catagen (C) skin. Numbers over peaks with
retention times different from NAS represent unknown products of
NAS changing metabolism through the different phases of the hair
cycle, e.g. telogen (A), anagen VI (B) and catagen (C).
Fig. 10. HPLC chromatogram shows transformation of N-acetylsero-
tonin to melatonin in ear (A and B) and S91melanoma (C and D)
extracts. Experimental incubation with N-acetylserotonin (A and C)
and corresponding control incubation without N-acetylserotonin (B

and D). The numbers represent the elution position of standards: 1,
melatonin; 2, N-acetylserotonin.
3342 A. Slominski et al.(Eur. J. Biochem. 270) Ó FEBS 2003
metabolites of the indoleamine. As NAS has been shown to
be a substrate for horseradish peroxidase [46] it is possible
that these metabolites could be the products of NAS
oxidation by skin hemoproteins. Although NAS oxidative
mechanisms have not been fully elucidated, it is possible that
its metabolites may include kynuramines (N
1
-acetyl-
N
2
-formyl-5-methoxykynuramine and N-acetyl-5-methoxy-
kynuramine), similar to the oxidation of melatonin [47,48].
To summarize, mouse skin has both the capability of
producing serotonin and the machinery for its extensive
metabolism. Data currently available suggest the model for
the serotoninergic pathway in the C57BL/6 mouse skin that
is presented in Fig. 11. It would involve stepwise transfor-
mation of tryptophan to serotonin including action by
tryptophan hydroxylase, serotonin metabolism by NAT-1
to NAS and further processing to unidentified products
(presumably kynuramine derivatives). An alternative degra-
dation pathway would include MAO with the production
of 5HTPOL and 5HIAA as intermediate products. This
interpretation is consistent with the work of Schallreuter
et al. [49–51] showing cutaneous synthesis of tetrahydro-
biopterin (a necessary cofactor for TPH) and expression of
MAO-A activity, and of Debiec-Rychter et al.[36]demon-

strating NAT-1 gene expression in rodent epidermis.
In mice, hair growth is a complex, highly synchronized
process regulating physiology and morphology of the
entire skin [19]. We now add serotonin acetylation to the
hair cycle phase-dependent skin functions. The constancy
of tryptamine acetylation throughout the hair cycle
emphasizes the selectivity of cutaneous NAT activity for
serotonin. Such selectivity could have physiological and
pathological significance because serotonin transformation
to NAS would limit serotonin effects in the skin (pro-
edema, vasodilatory, pruritogenic and proinflammatory
activities). The further metabolism of NAS in hair cycle-
dependent fashion implies an additional regulatory func-
tion of NAS in skin physiology.
In summary, we present the molecular and biochemical
characterization of the apparatus producing and metabo-
lizing serotonin and N-acetylserotonin in the skin of
C57BL/6 mouse. We define further some of the factors
determining the activity of this apparatus that include
anatomical location, phase of hair cycle and skin cell type.
Acknowledgements
We thank Dr D. Klein from NIH for antibodies against AANAT, Bis
inhibitor and constructive criticism, and Dr D. Bennett (St George’s
Hospital, London, UK) and Dr V. Hearing (NIH) for immortalized
mouse melanocytes (MelA). The work was supported in part by grants
from the Center of Excellence for Diseases of Connective Tissue,
UTHSC, and from the Center of Genomics and Bioinformatics,
UTHSC, to AS.
References
1. Slominski, A. & Wortsman, J. (2000) Neuroendocrinology of the

skin. Endocrine Rev. 21, 457–487.
2. Bos, J.D., Ed. (1997) Skin Immune System (Sis). Cutaneous
Immunology and Clinical Immunodermatology.CRCPress,Boca
Raton, FL.
3. Nordlund, J.J., Boissy, R.E., Hearing, V.J., King, R.A. &
Ortonne, J.P., eds. (1988) The Pigmentary System. Physiology and
Pathophysiology. Oxford University Press, New York and Oxford.
4. Slominski, A., Paus, R. & Schaderdorf, D. (1993) Melanocytes
are sensory and regulatory cells of epidermis. J. Theor. Biol. 164,
103–120.
5. Slominski, A., Wortsman, J., Luger, T., Paus, R. & Salomon, S.
(2000) Corticotropin releasing hormone and proopiomelanocortin
involvement in the cutaneous response to stress. Physiol. Rev. 80,
979–1020.
6. Schallreuter, K.U., Lemke, K.R., Pittelkow, M.R., Wood, J.M.,
Korner, C. & Malik, R. (1995) Catecholamines in human kerati-
nocyte differentiation. J. Invest. Dermatol. 104, 953–957.
7. Grando, S.A. & Horton, R.M. (1997) The keratinocyte choliner-
gic system with acetylcholine as an epidermal cytotransmitter. Cur.
Opin. Dermatol. 4, 462–268.
8. Slominski, A., Pisarchik, A., Semak, I., Sweatman, T., Szczes-
niewski, A. & Wortsman, J. (2002) Serotoninergic system in
hamster skin. J. Invest. Dermatol. 118, 1065–1072.
9. Slominski, A., Semak, I., Pisarchik, A., Sweatman, T., Szczes-
niewski, A. & Wortsman, J. (2002) Conversion of 1-tryptophan
to serotonin and melatonin in melanoma cells. FEBS Lett. 511,
102–106.
10. Johansson,O.,Liu,P Y.,Bondesson,L.,Nordlind,K.,Olsson,
M.J., Lontz, W., Verhofstad, A., Liang, Y. & Gangi, S. (1998) A
serotonin-like immunoreactivity is present in human cutaneous

melanocytes. J. Invest. Dermatol. 111, 1010–1014.
11. Slominski, A., Baker, J., Rosano, T., Guisti, L.W., Ermak, G.,
Grande, M. & Gaudet, S.J. (1996) Metabolism of serotonin to
N-acetylserotonin, melatonin, and 5-methoxytryptamine in ham-
ster skin culture. J. Biol. Chem. 271, 12281–12286.
12. Slominski, A., Ermak, H.J., Mazurkiewicz, J. & Corliss, E.A.
(1996) The expression of proopiomelanocortin (POMC) and of
corticotropin releasing hormone receptor (CRH-R.) genes in
mouse skin. Biochim. Biophys. Acta 1289, 247–251.
Fig. 11. Proposed model of serotoninergic pathway in the C57BL/6
mouse. The horizontal arrows represent inhibitory effect of CoA-S-N-
acetyltryptamine (Bis) or pargyline. TPH, 1; aromatic aminoacid
decarboxylase, 2; NAT-1, 3; MAO, 4; aldehyde dehydrogenase,
5; aldehyde reductase, 6. Question marks represent products of NAS
metabolism (for details see Discussion).
Ó FEBS 2003 Serotoninergic system in mouse skin (Eur. J. Biochem. 270) 3343
13. Kema, I.P., de Vries, E.G.E. & Muskiet, F.A.J. (2000) Clinical
chemistry of serotonin and metabolites. J. Chromatogr. B. 747,
33–48.
14. Mockus, S.M. & Vrana, K.E. (1998) Advances in the molecular
characterization of tryptophan hydroxylase. J. Mol. Neurosci. 10,
163–179.
15. Yu, H.S. & Reiter, R.J. (1993) Melatonin Biosynthesis, Physiolo-
gical Effects, and Clinical Implication. CRC Press, Boca Raton, FL.
16. Buznikov, G.A., Lambert, H.W. & Lauder, J.M. (2001) Serotonin
and serotonin-like substances as regulators of early embryogenesis
and morphogenesis. Cell Tissue Res. 305, 177–186.
17. Seuwen, K. & Pouysse
´
gur, J. (1990) Serotonin as a growth factor.

Biochem. Pharmacol. 39, 985–990.
18. Slominski, A. & Pawelek, J. (1998) Animals under the sun: effects
of UV radiation on mammalian skin. Clin. Dermatol. 16, 503–515.
19. Slominski, A. & Paus, R. (1993) Melanogenesis is coupled to
murine anagen: Toward new concepts for the role of melanocytes
and the regulation of melanogenesis in hair growth. J. Invest.
Dermatol. 101, 90S–97S.
20. Schallreuter, K.U., Beazley, W.D., Hibberts, N.A., Tobin, D.J.,
Paus, R. & Wood, J.M. (1998) Pterins in human hair follicle cells
and in the synchronised murine hair cycle. J. Invest. Dermatol. 111,
545–550.
21. Paus, R., Peters, E.M.J., Eichmueller, S. & Botchkarev, V.A.
(1997) Neural mechanisms of hair growth control. J. Invest.
Dermatol. Symp Proc. 2, 61–68.
22. Slominski, A., Moellmann, G., Kuklinska, E., Bomirski, A. &
Pawelek, J. (1988) Positive regulation of melanin pigmentation by
two key substrates of the melanogenic pathway: 1-tyrosine and
1-dopa. J. Cell Sci. 89, 287–296.
23. Thomas, K.B., Zawilska, J. & Iuvone, P.M. (1990) Arylalkyl-
amine (serotonin) N-acetyltransferase assay using high-perfor-
mance liquid chromatography with fluorescence or electrochemi-
cal detection of N-acetyltryptamine. Anal. Biochem. 184, 228–234.
24. Slominski, A., Pisarchik, A., Semak, I., Sweatman, T., Wortsman,
J., Szczesniewski, A., Slugocki, G., McNulty, J., Kauser, S. &
Tobin, D.J. (2002) Serotoninergic and melatoninergic systems are
fully expressed in human skin. FASEB J. 16, 896–898.
25. Pisarchik, A. & Slominski, A. (2001) Alternative splicing of CRH-
R1 receptors in human and mouse skin: Identification of new
variants and their differential expression. FASEB J. 15, 2754–
2756.

26. Roseboom, P.H., Namboodiri, M.A.A., Zimonjic, D.B., Popescu,
N.C., Rodriguez, I.R., Gastel, J.A. & Klein, D.C. (1998) Natural
melatonin, ÔknockdownÕ in C57BL/6J mice: rare mechanism
truncates serotonin N-acetyltransferase. Brain Res. 63, 189–197.
27. Nakata, H., & Hitoshi, F. (1982) Tryptophan 5-monooxygenase
from mouse mastocytoma, P815. A simple purification and gen-
eral properties. J. Biochem. 124, 595–601.
28. Kojima, M., Oguro, K., Sawabe, K., Iida, Y., Ikeda, R.,
Yamashita, A., Nakanishi, N. & Hasegawa, H. (2000) Rapid
turnover of tryptophan hydroxylase is driven by proteasomes in
RBL2H3 cells, a serotonin producing mast cell line. J. Biochem.
127, 121–127.
29. Hasegawa, H., Kojima, M., Oguro, K. & Nakanishi, N. (1995)
Rapid turnover of tryptophan hydroxylase in serotonin producing
cells: demonstration of ATP-dependent proteolytic degradation.
FEBS Lett. 368, 151–154.
30. Wang, G A., Coon, S.L. & Kaufman, S. (1998) Alternative
splicing at the 3¢–cDNA of human tryptophan hydroxylase.
J. Neurochem. 71, 1769–1772.
31. Boularand, S., Darmon, M.C. & Mallet, J. (1995) The human
tryptophan hydroxylase gene. An unusual splicing complexity in
the 5¢–untranslated region. J. Biol. Chem. 270, 3748–3756.
32.Sim,E.,Hickman,D.,Coroneos,E.&Kelly,S.L.(1992)
Arylamine N-acetyltransferase. Biochem. Soc. Trans. 20, 304–311.
33. Williams, J.A. & Phillips, D.H. (2000) Mammary expression of
xenobiotic metabolizing enzymes and their potential role in breast
cancer. Cancer Res. 60, 4667–4677.
34. Zemer, T.V., Lakshmi, V.M., Rustan, T.D., Doll, M.A., Deitz,
A.C., Davis, B.B. & Hein, D.W. (1996) Human N-acetylation of
benzidine: role of NAT1 and NAT2. Cancer Res. 56, 3941–3947.

35. Sadrieh, N., Davis, C.D. & Snyderwine, E.G. (1996) N-acetyl-
transferase expression and metabolic activation of the flood-
derived heterocyclic amines in the human mammary gland. Cancer
Res. 56, 2683–2687.
36. Debiec-Rychter, M., Land, S.J. & King, C.M. (1996) Histological
localization of messenger RNAs for rat acetyltransferases that
acetylate serotonin and genotoxic arylamines. Cancer Res. 56,
1517–1525.
37. Kawakubo, Y., Merk, H.F., Masacudi, T.A., Siebe, S. & Blo-
meke, B. (2000) N-acetylation of paraphenylenediamine in human
skin and keratinocytes. J. Pharmacol. Exp. Ther. 292, 150–155.
38. Kawakubo, Y., Manabe, S., Yamazoe, Y., Nishikawa, T. & Kato,
R. (1988) Properties of cutaneous acetyltransferase catalyzing
N- and O-acetylation of carcinogenic arylamines and N-hydro-
xyarylamine. Biochem. Pharmacol. 37, 265–270.
39. Coon, S.L., Weller, J.L., Korf, H W., Namboordiri, M.A.A.,
Rollag, M. & Klein, D.C. (2001) cAMP regulation of arylalk-
ylamine N-acetyltransferase (AANAT, EC 2.3.1.87). A new cell
line (1E7) provides evidence of intracellular AANAT activation.
J. Biol. Chem. 276, 24097–24107.
40. Khalil, E. & Cole, P. (1998) A potent inhibitor of the melatonin
rhythm enzyme. J. Am. Chem. Soc. 120, 6195–6196.
41. Gaudet, S., Slominski, A., Etminan, M., Pruski, D., Paus, R. &
Namboodiri, M.A.A. (1993) Identification and characterization of
two isozymic forms of arylamine N-acetyltransferase in Syrian
hamster skin. J. Invest. Dermatol. 101, 660–665.
42. Goto, M., Oshima, I., Tomita, T. & Ebihara, S. (1989) Melatonin
content of the pineal gland in different mouse strains. J. Pineal
Res. 7, 195–204.
43. Conti,A.,Conconi,S.,Hertens,E.,Skwarlo-Sonta,K.,Mark-

owska, M. & Maestroni, G.J.M. (2000) Evidence for melatonin
synthesis in mouse and human bone marrow cells. J. Pineal Res.
28, 193–202.
44. Reiter, R.I. (1991) Pineal melatonin: cell biology of its synthesis
and of its physiological interactions. Endocrine Rev. 12, 151–180.
45. Valoti, M., Moron, J.A., Benocci, A., Sgaragli, G. & Unzeta. M.
(1988) Evidence of a coupled mechanism between monoamine
oxidase and peroxidase in the metabolism of tyramine by rat
intestinal mitochondria. Biochem. Pharmacol. 55, 37–43.
46. Siraki, A.G. & O’Brien, P.J. (2002) Prooxidant activity of free
radicals derived from phenol-containing neurotransmitters. Toxi-
cology. 177, 81–90.
47. De Oliveira Silva, S., Ximenes, V.F., Catalani, L.H. & Campa, A.
(2000) M yelop ero x ida s e-c a tal y ze d oxi d ati o n o f m e lat o ni n b y a c ti-
vated neutrophils. Biochem. Biophys. Res. Commun. 279, 657–662.
48. Allegra, M., Furtmuller, P.G., Regelsberger, G., Turco-Liveri,
M.L.,Tesoriere,L.,Perretti,M.,Livrea,M.A.&Obinger,C.
(2001) Mechanism of reaction of melatonin with human myelo-
peroxidase. Biochem. Biophys. Res. Commun. 282, 380–386.
49. Schallreuter, K.U., Schulz-Douglas, V., Bunz, A., Beazley, W.D.
& Korner, C. (1997) Pteridines in the control of pigmentation.
J. Invest. Dermatol. 109, 31–35.
50. Schallreuter, K.U., Wood, J.M., Pittelkow, M.R., Buttner, G.,
Swanson, N., Korner, C. & Ehrke, C. (1996) Increased mono-
amine oxidase a activity in the epidermis of patients with vitiligo.
Arch. Dermatol. Res. 288, 14–18.
51. Schallreuter, K.U., Wood, J.M., Pittelkow, M.R., Gu
ˆ
tlich, M.,
Lemke,R.,Rodl,W.,Swanson,N.N.,Hitzemann,K.&Ziegler,I.

(1994) Regulation of melanin biosynthesis in the human epidermis
by tetrahydrobiopterin. Science 263, 1444–1446.
3344 A. Slominski et al.(Eur. J. Biochem. 270) Ó FEBS 2003