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.
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. By contrast, UniProt identifiers uniquely specify a protein by its amino acid sequence.
For example, the tripeptide aminopeptidases have the code "EC 188.8.131.52", whose components indicate the following groups of enzymes:
|Group||Reaction catalyzed||Typical reaction||Enzyme example(s) with trivial name|
|To catalyze oxidation/reduction reactions; transfer of H and O atoms or electrons from one substance to another|| AH + B → A + BH (reduced)|
A + O → AO (oxidized)
| EC 2|
|Transfer of a functional group from one substance to another. The group may be methyl-, acyl-, amino- or phosphate group||AB + C → A + BC||Transaminase, kinase|
| EC 3|
|Formation of two products from a substrate by hydrolysis||AB + H2O → AOH + BH||Lipase, amylase, peptidase|
| EC 4|
|Non-hydrolytic addition or removal of groups from substrates. C-C, C-N, C-O or C-S bonds may be cleaved||RCOCOOH → RCOH + CO2||Decarboxylase|
| EC 5|
|Intramolecule rearrangement, i.e. isomerization changes within a single molecule||AB → BA||Isomerase, mutase|
| EC 6|
|Join together two molecules by synthesis of new C-O, C-S, C-N or C-C bonds with simultaneous breakdown of ATP||X + Y+ ATP → XY + ADP + Pi||Synthetase|
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.
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