2. 1. Introduction
2. Classification of enzyme
I. Oxidoreductases
II. Transferases
III. Hydrolases
IV. Lyases
V. Isomerases
VI. Ligases or Synthetases
3. Catalytic Sites
4. Mechanism of Enzyme
3. • It was first introduced by w. Kuhne in 1878.
• Enzymes are protein catalysts for biochemical
reaction in living cells
• The term enzyme derived from Greek means "in
yeast" because the yeast cells were first to reveal
enzyme activity in organism.
4. Oxidoreductases: The group, in fact, includes
those enzymes which bring about oxidation-reduction
reactions between two substrates.
Transferases: Enzymes which catalyze the transfer of a
group, G (other than hydrogen) between a pair of substrates, S
and S′ are called transferases.
e.g. Acyltransferases, Glycosyltransferases
CLASSIFICATION OF ENZYMES
According to IUB Six classes have been recognized of enzymes on the basis
of their reaction specificity.
5. Hydrolases: These catalyze the hydrolysis of their
substrates by adding constituents of water across the bond
they split. The substrates include ester, glycosyl, ether,
peptide, acid-anhydride, C—C, halide and P—N bonds.
e.g. β-galactosidase, Lipase
Lyases (= Desmolases): These are those enzymes
which catalyze the removal of groups from substrates by
mechanisms other than hydrolysis, leaving double bonds.
6. Isomerases:
These catalyze interconversions of optical, geometric or
positional isomers by intramolecular rearrangement of atoms
or groups.
E.g. Glucose-6-phosphate==fructose-6- phosphate
Ligases or Synthetases:
These are the enzymes catalyzing the linking together of two
compounds utilizing the energy made available due to
simultaneous breaking of a pyrophosphate bond in ATP or a
similar compound.
7. CATALYTIC SITES
As the substrate molecules are comparatively much
smaller than the enzyme molecules, there should be
some specific regions or sites on the enzyme for
binding with the substrate. Such sites of attachment
are variously called as ‘active sites’ or ‘catalytic
sites’ or ‘substrate sites’.
