Classification of enzymes based on the recommendations of the Committee on Enzyme Nomenclature of the International Union of Biochemistry.
The first number indicates the broad type of enzyme (1 = oxidoreductase, 2 = transferase, 3 = hydrolase, 4 = lyase, 5 = isomerase, 6 = ligase (synthetase)).
The second and third numbers indicate subsidiary groupings and the last number, which is unique, is assigned arbitrarily in numerical order by the Committee.
(08 Mar 2000)