A classification of enzymes according to the Enzyme Commission of the International Union of Biochemistry and Molecular Biology. Enzymes are allocated four numbers, the first of which defines the type of reaction catalyzed, the next two define the substrates, and the fourth is a catalogue number. Categories of enzymes are EC 1, Oxidoreductases; EC 2, Transferases; EC 3, Hydrolases; EC 4, Lyases; EC 5, Isomerases; EC 6, Ligases (Synthetases).
