Classification of enzymes : 

Oxidoreductase/dehydrogenases : Catalyse oxidoreduction between 2 substrates. 

Transferases : Catalyse transfer of a group between a pair of substrates. 

Hydrolases : Catalyse hydrolysis of ester, ether, peptide, glycosidic, C-C, P-N bonds. 

Lyases : Catalyse removal of groups from substrates by mechanisms other than hydrolysis. 

Isomerases : Catalyse inter-conversion of optical, geometric or positional isomers. 

Ligases : Catalyse linking together of 2 compounds. 

Cofactors : Non-protein constituents found to the enzyme to make it catalytically active. Protein portion of enzyme is called apoenzyme. 

• Prosthetic groups : Are organic compounds tightly bound to apoenzyme. E.g., haem in peroxydase and catalase. 

• Co-enzymes : Organic compounds which has transient association with enzyme. E.g., NAD, NADP. 

• Metal ions : Required for enzyme activity. Form coordination bond with side chains at active site and with substrate. E.g., zinc is a co-factor for enzyme carboxypeptidase.