This document discusses the classification of enzymes by the International Union of Biochemistry. It states that enzymes are divided into 6 main classes - oxidoreductases, transferases, hydrolases, lyases, isomerases, and ligases - based on the type of chemical reactions they catalyze. Each enzyme is assigned a 4-digit code number indicating its class, subclass, and identity. The document also describes the three types of cofactors that can bind to enzymes and enable their catalytic activity: prosthetic groups, coenzymes, and metal ions.
2. • Thousands of enzymes have been discovered, isolated
and studied.
3. • Most of these enzymes have been classified into
different groups based on the type of reactions they
catalyse.
• Enzymes are divided into 6 classes each with 4-13
subclasses and named accordingly by a four-digit
number.
4. International Union of Biochemistry (IUB).
Based on their action they are divided into 6 major classes.
Each enzyme is assigned a 4 Digit code number.
(i) the first number shows enzyme classes.
Ii). the second figure indicates the subclass,
(iii) the third figure gives the sub-subclass,
(iv) the fourth figure is the serial number of the enzyme in its sub-
subclass.
11. Lyases:
• Enzymes that catalyse removal of groups from substrates
by mechanisms other than hydrolysis leaving double
bonds..
12. • Isomerases: Includes all enzymes catalysing inter-
conversion of optical, geometric or positional isomers.
• Ligases: Enzymes catalysing the linking together of 2
compounds, e.g
• catalyse joining of C-O, C-S, C-N, P-O etc.
15. • Enzymes are composed of one or several polypeptide
chains.
• In number of cases in which non-protein part called
cofactors are bound to the the enzyme to make the
enzyme catalytically active.
• Catalytic activity is lost when the co-factor is removed
from the enzyme.
16. • In these instances, the protein portion of the enzymes is
called the apoenzyme.
• Three kinds of cofactors may be identified:
• prosthetic groups,
• co-enzymes
• metal ions.
17. Three kinds of cofactors
• Prosthetic groups
• Co-enzymes
• metal ions
18. Prosthetic groups
• Prosthetic groups are organic compounds and are
distinguished from other cofactors in that they are
tightly bound to the apoenzyme.
19. Prosthetic groups
• For example: In peroxidase and catalase, which catalyze
the breakdown of hydrogen peroxide to water and
oxygen.
• In peroxidase and catalase haem is the prosthetic group
and it is a part of the active site of the enzyme.
20. Co-enzymes
• Co-enzymes are also organic compounds but their
association with the apoenzyme is only transient,
usually occurring during the course of catalysis.
• Coenzymes are vitamins.
• NAD and NADP contain the vitamin niacin.
Nicotinamide adenine dinucleotide (NADH)
Nicotinamide adenine dinucleotide phosphate (NADPH)
21. Metal ions
• A number of enzymes require metal ions for their
activity.
• Metal ions form coordination bonds with side chains at
the active site and at the same time form one or more
coordination bonds with the substrate,
• e.g: Zn is a cofactor for the proteolytic enzyme carboxy-
peptidase.
22. • The technological function of carboxypeptidase is to
release C-terminal amino acids from proteins