System of classification
The Enzyme Commission divided enzymes into 6 main classes, on the basis of the total reaction catalyzed. Each enzyme was assigned a code number; consisting of four elements, separated by dots. The first digit shows to which of the main classes the enzyme belongs, as follows:
First digit Enzyme class Type of reaction catalyzed
1 Oxido-reductases Oxidation/reduction reactions
2 Transferases Transfer of an atom or group between two molecules.
3 Hydrolases Hydrolysis reactions
4 Lyases Removal of a group from substrate (not be hydrolysis)
5 Isomerases Isomerization reactions
6 Ligases The synthetic joining of two molecule.