: ''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 [[numbering scheme|numerical classification]] scheme for [[enzyme]]s, based on the [[chemical reaction]]s they [[catalysis|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.<ref>{{cite web
| publisher = ExPASy
| title = ENZYME (Enzyme nomenclature database)
| url = http://www.expasy.org/enzyme/
| accessdate = 2006-03-14
}}</ref>

==Format of number==
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 [[tripeptide aminopeptidase]]s have the code "EC 3.4.11.4", whose components indicate the following groups of enzymes: 

* ''EC 3'' enzymes are [[hydrolase]]s (enzymes that use [[water]] to break up some other molecule)
* ''EC 3.4'' are hydrolases that act on [[peptide bond]]s
* ''EC 3.4.11'' are those hydrolases that cleave off the amino-terminal [[amino acid]] from a [[polypeptide]]
* ''EC 3.4.11.4'' are those that cleave off the amino-terminal end from a [[tripeptide]]

==Top level codes==
{| class="wikitable"
|+ Top-level EC numbers<ref>{{cite web
| last = Moss
| first = G.P.
| title = Recommendations of the Nomenclature Committee
| publisher = International Union of Biochemistry and Molecular Biology on the Nomenclature and Classification of Enzymes by the Reactions they Catalyse
| url = http://www.chem.qmul.ac.uk/iubmb/enzyme/
| accessdate = 2006-03-14}}</ref>
|-
! Group
! Reaction catalyzed
! Typical reaction
! Enzyme example(s) with trivial name
|-
! |EC 1<br />''[[Oxidoreductase]]s''
| To catalyze [[oxidation]]/reduction reactions;  transfer of H and O atoms or [[electron]]s from one substance to another
| AH + B → A + BH (<small>'''reduced'''</small>)<br /> A + O → AO (<small>'''oxidized'''</small>)
| [[Dehydrogenase]], [[oxidase]]
|-
! EC 2<br />''[[Transferase]]s''
| 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<br />''[[Hydrolase]]s''
| Formation of two products from a substrate by  [[hydrolysis]]
| AB + H<sub>2</sub>O → AOH + BH
| [[Lipase]], [[amylase]], [[peptidase]]
|-
! EC 4<br />''[[Lyase]]s''
| Non-hydrolytic addition or removal of groups from substrates. C-C, C-N, C-O or C-S bonds may be cleaved
| RCOCOOH → RCOH + CO<sub>2</sub>
|
|-
! EC 5<br />''[[Isomerase]]s''
| Intramolecule rearrangement, i.e. [[isomer|isomerization]] changes within a single molecule
| AB → BA</td>
| [[Isomerase]], [[mutase]]
|-
! EC 6<br />''[[Ligase]]s''
| Join together two molecules by synthesis of new C-O, C-S, C-N or C-C [[covalent bond|bonds]] with simultaneous breakdown of [[Adenosine triphosphate|ATP]]
| X + Y+ ATP → XY + ADP + Pi
| [[Synthetase]]
|}

==History==
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.

==References==
<references/>

==See also==
* [[TC number]] (classification of membrane transport proteins)
* [[List of enzymes]]

{{Enzymes}}
[[Category:Enzymes]]
[[Category:Classification systems]]

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