IUBMB Classification of enzymes

1. Classification of
enzymes
Namrata Chhabra
M.D. Biochemistry
15-May-20 Namrata Chhabra 1

2. • Biologic polymers that catalyze the chemical reactions
• Enzymes are neither consumed nor permanently altered because of
their participation in a reaction
• Except for catalytic RNA molecules, or ribozymes, enzymes are
proteins in nature.
• In addition to being highly efficient, enzymes are also extremely
selective catalysts.
Enzymes- Introduction
15-May-20 Namrata Chhabra 2

3. Nomenclature of enzymes
a) Based on the type of reaction catalyzed (followed by the suffix –ase)
b) Based on the nature of substrate
c) Based on the source of enzyme
d) Based on its regulation
e) Trival names
15-May-20 Namrata Chhabra 3

4. Nomenclature of enzymes
Based on the type of reaction catalyzed (followed by the suffix –ase)
• Dehydrogenase
• Protease
• Isomerase
• Reductase
• Transferase
15-May-20 Namrata Chhabra 4

5. Nomenclature of enzymes
Based on the nature of substrate
• Glucokinase
• Hexokinase
• Xanthine oxidase
• Alcohol dehydrogenase
15-May-20 Namrata Chhabra 5

6. Nomenclature of
enzymes
Based on the source of
enzyme
• Pancreatic lipase
• Gastric lipase
• Salivary amylase
• Muscle phosphorylase
• Hepatic phosphorylase
15-May-20 Namrata Chhabra 6

7. Nomenclature of enzymes
Based on its regulation
• Hormone specific lipase
Random names
• Trypsin
• Pepsin
• Thrombin
15-May-20 Namrata Chhabra 7

8. Systematic Names of enzymes
• The International Union of Biochemists (IUB) classification
• Each enzyme has a unique name and code number that identifies the
type of reaction catalyzed, and the substrates involved.
• Enzymes are grouped into six classes.
15-May-20 Namrata Chhabra 8

9. Class-1- Oxidoreductases
The oxidoreductases catalyze the transfer of reducing
equivalents(hydrogen and electrons)from one redox system to another.
Examples: Dehydrogenase, oxidase, oxygenase, hydro peroxidase
• Lactate dehydrogenase
• Alcohol dehydrogenase
• Aldehyde dehydrogenase
• Xanthine oxidase
• Cytochrome oxidase
15-May-20 Namrata Chhabra 9

10. Reaction catalyzed by dehydrogenase
15-May-20 Namrata Chhabra 10

11. Class 2- Transferases
The transferases catalyze the transfer of other groups from one
molecule to another.
Oxidoreductases and transferases generally require coenzymes.
Examples:
• Amino transferase
• Glucosyl transferase
• Methyl transferase
• Phospho transferase
15-May-20 Namrata Chhabra 11

12. Reaction catalyzed by transferase
15-May-20 Namrata Chhabra 12

13. Class 3- Hydrolases
The hydrolases cause cleavage of bond using water.
Examples:
• Protease
• Peptidase
• Glycosidase
• Phosphatase
15-May-20 Namrata Chhabra 13

14. Reaction catalyzed by hydrolase
15-May-20 Namrata Chhabra 14

15. Class 4 Lyases
• The Lyases catalyze reactions involving either the cleavage or
formation of chemical bonds (also known as synthases)
• with double bonds either arising or disappearing
• Cleavage of bond does not require water.
• Lyases usually break C-C, C-O, C-N, or C-S linkages.
Examples:
Fumarase, Arginosuccinase, glutamate decarboxylase
15-May-20 Namrata Chhabra 15

16. Reaction
catalyzed by
Lyase
15-May-20 Namrata Chhabra 16

17. Class 5- Isomerases
• The isomerases move groups within a molecule, without changing
the gross composition of the substrate.
Examples:
• Epimerase
• Aldose ketose isomerase
• Mutase
15-May-20 Namrata Chhabra 17

18. Reaction catalyzed by Isomerase
15-May-20 Namrata Chhabra 18

19. Class 6- Ligases
• The ligation reactions catalyzed by ligases (“synthetases,” class 6) are
energy-dependent and are therefore always coupled to the hydrolysis
of nucleoside triphosphates.
Examples:
• DNA Ligase
• Pyruvate carboxylase
• Acetyl Co A carboxylase
15-May-20 Namrata Chhabra 19

20. Reaction catalyzed by Ligase
15-May-20 Namrata Chhabra 20

21. Enzyme Commission number (EC number)
• Each enzyme is entered in the Enzyme Catalogue with a four-digit
Enzyme Commission number (EC number).
• The first digit indicates membership of one of the six major classes.
The next two indicate subclasses and sub-subclasses.
• The last digit indicates where the enzyme belongs in the sub-subclass.
15-May-20 Namrata Chhabra 21

22. Enzyme Commission number (EC number)
• The IUB name of hexokinase is ATP:D-hexose 6-phosphotransferase
E.C. 2.7.1.1.
• This name identifies hexokinase as a member of class 2 (transferases),
subclass 7 (transfer of a phosphoryl group),
• sub-subclass 1 (alcohol is the phosphoryl acceptor),
• and "hexose-6" indicates that the alcohol phosphorylated is on
carbon six of a hexose.
• However, it is still called as hexokinase.
15-May-20 Namrata Chhabra 22

23. 15-May-20 Namrata Chhabra 23

24. Thank you
15-May-20 Namrata Chhabra 24