Chapter 4 lipid 2015817

Chuyển hóa lipid (degradation, catabolism)
• Thủy phân
• Oxy hóa khử sinh học


• Các enzym thủy phân lipid:
– Lipase
– Phospholipase A,B,C,D

• Các sản phẩm thủy phân:
– Glycerol
– Axit béo


Entry of glycerol into the glycolytic pathway


Chuyển hóa của axit béo
Chu trình -oxy hóa axit béo (Knoop)
• Các axit béo mạch thẳng, số chẵn nguyên tử C
• Các axit béo no
• Các axit béo không no
α -Oxy hóa
• Oxy hóa axít béo số C lẻ


Fatty acid beta oxidation
CAPILLARY
lipoproteins

LPL

FA
FA
albumin
FA
1
From fat cell

2
FA

MITOCHONDRION

FABP
FA
3

4

FABP

acyl-CoA
FABP

FA

CYTOPLASM

cell membrane

A

C
S

TCA
cycle 7
-oxidation
6
acyl-CoA

acetyl-CoA

5
carnitine
transporter

FA = fatty acid
LPL = lipoprotein lipase
FABP = fatty acid binding protein
ACS = acyl CoA synthetase


Conversion of a fatty acid to an acyl-CoA


β-Oxidation of Acyl-CoA to aceyl-CoA


Steps in Beta Oxidation
• Fatty Acid Activation by esterification with
CoASH

• Membrane Transport of Fatty Acyl CoA Esters
• Carbon Backbone Reaction Sequence
•
•
•
•

Dehydrogenation
Hydration
Dehydrogenation
Thiolase Reaction (Carbon-Carbon Cleavage)


1. Activation of Fatty Acids
• Acyl CoA synthetase reaction occurs on the
mitochondrial membrane


2.Transport into Mitochondrial Matrix
• Carnitine carries
long-chain
activated fatty
acids into the
mitochondrial
matrix


• Carnitine carries long-chain activated fatty
acids into the mitochondrial matrix

3. Fatty acid Beta oxidation
• Each round in fatty
acid degradation
involves four reactions
– 1. oxidation to
trans-∆2-Enoly-CoA

Removes H atoms from the
 and  carbons
-Forms a trans C=C bond
-Reduces FAD to FADH2

 


2. Hydration to L–3–
Hydroxylacyl CoA
– Adds water across the
trans C=C bond
– Forms a hydroxyl group
(—OH) on the  carbon


3. Oxidation to
– 3–Ketoacyl CoA
– Oxidizes the hydroxyl
group
– Forms a keto group on the
 carbon

4. Thiolysis to produce
Acetyl–CoA
– acetyl CoA is cleaved:By
splitting the bond between
the  and  carbons.
– To form a shortened fatty
acyl CoA that repeats steps
1 - 4 of -oxidation


Cycles of -Oxidation
The length of a fatty acid
• Determines the number of oxidations and the total
number of acetyl CoA groups
Carbons in Acetyl CoA
-Oxidation Cycles
Fatty Acid
(C/2)
(C/2 –1)
12
6
5
14
7
6
16
8
7

18
9
8


-Oxidation and ATP
Activation of a fatty acid requires:
2 ATP
One cycle of oxidation of a fatty acid produces:
1 NADH
3 ATP
1 FADH2
2 ATP
Acetyl CoA entering the citric acid cycle produces:
1 Acetyl CoA
12 ATP


ATP for Myristic Acid C14
ATP production for Myristic(14 carbons):
Activation of myristic acid
-2 ATP
7 Acetyl CoA
7 acetyl CoA x 12 ATP/acetyl CoA
84 ATP
6 Oxidation cycles
6 NADH x 3ATP/NADH
18 ATP
6 FADH2 x 2ATP/FADH2
12 ATP

Total

112 ATP


The β-oxidation pathway of Palmitic acid
The β-Oxidation of Saturated Fatty
Acids: 4 Basic Steps
from Palmitoyl-CoA


Oxidation of Fatty Acids