1. Classification of enzymes. Units of enzyme activity.1

2. Naming of Enzymes Common names
are formed by adding the suffix –ase to the name of substrate
Example: tyrosinase catalyzes oxidation of tyrosine; cellulase catalyzes the hydrolysis of cellulose
Common names don’t describe the chemistry of the reaction
Trivial names
Example: pepsin, catalase, trypsin.
Don’t give information about the substrate, product or chemistry of the reaction 2

3. Principle of the international classification
All enzymes are classified into six categories according to the type of reaction they catalyze
Each enzyme has an official international name ending in –ase
Each enzyme has classification number consisting of four digits: EC:
First digit refers to a class of enzyme, second -to a subclass, third – to a subsubclass, and fourth means the ordinal number of enzyme in subsubclass 3

4. The Six Classes of Enzymes
1. Oxidoreductases
Catalyze oxidation-reduction reactions
- oxidases peroxidases dehydrogenases 4

5. 2. Transferases
Catalyze group transfer reactions 5

6. 3. Hydrolases
Catalyze hydrolysis reactions where water is the acceptor of the transferred group
- esterases peptidases glycosidases 6

7. 4. Lyases
Catalyze lysis of a substrate, generating a double bond in a nonhydrolytic, nonoxidative elimination 7

8. 5. Isomerases
Catalyze isomerization reactions 8

9. 6. Ligases (synthetases)
Catalyze ligation, or joining of two substrates
Require chemical energy (e.g. ATP) 9