Enzyme Commission number

Enzyme Commission number (EC number) is a numerical classification scheme for enzymes, based on the chemical reactions they catalyze. As a system of enzyme nomenclature, every EC number is associated with a recommended name for the respective enzyme.

Strictly speaking, EC numbers do not specify enzymes, but rather enzyme-catalyzed reactions. If different enzymes (for example from different organisms) catalyze the same reaction, then they receive the same EC number. Furthermore, through evolution, enzymes may lose their original function and gain a new one, in a process called enzyme evolution. In such a case, they will receive a new EC number.

Structure of EC numbers

An EC number has the format EC x.y.z.w where x, y, z, w are integers. The numbers are arranged in a hierarchical fashion, where x is the top level and represents one of the six main classes:

• EC 1: Oxidoreductases: enzymes that catalyze oxidation/reduction reactions.
• EC 2: Transferases: enzymes that transfer a functional group (e.g. a methyl or phosphate group) from one molecule to another.
• EC 3: Hydrolases: enzymes that catalyze the hydrolysis of various bonds.
• EC 4: Lyases: enzymes that cleave various bonds by means other than hydrolysis and oxidation.
• EC 5: Isomerases: enzymes that catalyze geometric or structural changes within one molecule.
• EC 6: Ligases: enzymes that join together two molecules with covalent bonds.

History and administration

The EC number system was first introduced by the International Union of Biochemistry and Molecular Biology (IUBMB) in 1961. The system is continuously updated by the IUBMB. The current version is the "Enzyme Nomenclature 1992" supplemented with subsequent amendments and additions.

See also

• Protein Data Bank
• Enzyme catalysis
• Enzyme kinetics