Classification of enzymes. Units of enzyme activity. 1

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

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: 2.3.4.2 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

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

2. Transferases Catalyze group transfer reactions 5

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

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

5. Isomerases Catalyze isomerization reactions 8

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