Chapter 3 enzyme 2015814

CHAPTER 3

ENZYME


CONTENTS
 Nomenclature and Classification
 Mechanism of enzyme action
 Catalytic mechanism
 Enzyme activity
 Factors influence on enzyme activity
 Enzyme Kinetics
 Enzyme production

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ENZYME NOMENCLATURE
 Traditional name: some of the earliest enzymes to be
discovered:
 Name: ending in – “in” to indicate they were proteins
 Ex: the digestive enzymes: pepsin, trypsin, chymotrypsin

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ENZYME NOMENCLATURE

 Common name
Substrate/
activity

+

ase

 Examples:
 urease catalyzes hydrolysis of urea
 DNA polymerase catalyzes the polymerization of
nucleotides to form DNA

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EXAMPLES

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ENZYME NOMENCLATURE
 EC (Enzyme Commission) systematic name:
 [International Union of Biochemistry and Molecular
Biology: IUBMB]
 Systematic name indicating:


The substance acted on

The functional group acted on

The type of reaction catalyzed
 All EC names end in –ase
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ENZYME NOMENCLATURE
Systematic name: encoded by a four-digit
classification number
 Ex: EC number: 2.7.1.1.:
 (2) : the class name (transferase)
 (7): the sub class (phosphotransferase)
 (1): the sub sub class (a phosphotransferase
with a hydroxyl group as acceptor)
 (1): the sub sub sub class (D-hexose as the
phosphoryl group acceptor)
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EC CLASSIFICATION OF ENZYMES
Enzymes: grouped into 6 major classes (based on the rxns
which they catalyze)

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ENZYME CLASSIFICATION

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ENZYME CLASSIFICATION

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Oxidoreductases, Transferases and Hydrolases


Lyases, Isomerases and Ligases


OXIDOREDUCTASE
 Ex: dehydrogenases (Lactate Dehydrogenase
(LDH)): accept and donate electrons (H+), using
cofactors such as NAD+/NADH as an electron

donor or acceptor

LDH

R

NAD+
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R

NADH
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Lyases
 Lyases: cleaving bonds
 Ex: aldolases: fructose diphosphate aldolase: in glycolysis)
 Thiolases: β-ketoacyl-CoA thiolase: breakdown of fatty acids

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Isomerases

 Isomerases: catalyzing the rearrangement of atoms in a molecule

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Ligases
 Ligases: catalyzing synthesis of bonds

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ENZYME NOMENCLATURE

 Ex: EC number: 2.7.1.1.:
 (2) : the class name (transferase)
 (7): the sub class (phosphotransferase)
 (1): a phosphotransferase with a hydroxyl group
as acceptor
 (1): D-hexose as the phosphoryl group acceptor

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CLASSWORK
?: Predict the substrates for the following enzymes:
a) Maltase
b) Peptidase
c) Glucose 6-phosphate isomerase

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CLASSWORK
? Match the following general enzyme names to the
reactions that they catalyze
Enzyme

Reaction catalyzed

Decarboxylase

Hydrolysis of cellulose

Peptidase

Hydrolysis of pectin

Pectinase

Hydrolysis of peptide linkages

Lipase

Removal of carboxyl groups from compounds

Cellulase

Hydrolysis of lipid

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STRUCTURE OF AN ENZYME
 Some enzymes are proteins
 Some enzyme are RNAs
 Some contains both a protein (apoprotein/apoenzyme)
and a nonprotein
 Nonprotein: either a coenzyme (vitamins) or a
cofactor (inorganic ions)
 Some enzymes require both a coenzyme and one
cofactor for activity
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