EC number


 * This article is about the Enzyme Commission codes. For the European Commission system for coding chemicals, see EC-No.

The 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.

Every enzyme code consists of the letters "EC" followed by four numbers separated by periods. Those numbers represent a progressively finer classification of the enzyme. For example, the enzyme tripeptide aminopeptidase has the code "EC 3.4.11.4", whose components indicate the following groups of enzymes: EC 3 enzymes are hydrolases (enzymes that use water to break up some other molecule), EC 3.4 are hydrolases that act on peptide bonds, EC 3.4.11 enzymes are only those hydrolases that cleave off the amino-terminal amino acid from a polypeptide, and EC 3.4.11.4 are those that cleave off the amino-terminal end from a tripeptide.

Strictly speaking, EC numbers do not specify enzymes, but enzyme-catalyzed reactions. If different enzymes (for instance from different organisms) catalyze the same reaction, then they receive the same EC number. UniProt identifiers uniquely specify a protein by its amino acid sequence.

The enzyme nomenclature scheme was developed starting in 1955, when the International Congress of Biochemistry in Brussels set up an Enzyme Commission. The first version was published in 1961. The current sixth edition, published by the International Union of Biochemistry and Molecular Biology in 1992, contains 3196 different enzymes.