Editing Enzyme Commission number

{{Short description|Chemical numbering scheme}}
{{Distinguish|European Community number}}
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]].<ref name="isbn0-12-227164-5">{{cite book |last=Webb |first=E. C. |title=Enzyme nomenclature 1992: recommendations of the Nomenclature Committee of the International Union of Biochemistry and Molecular Biology on the nomenclature and classification of enzymes |publisher=Academic Press |year=1992 |isbn=978-0-12-227164-9 |url=https://archive.org/details/enzymenomenclatu0000inte_d6c2 |url-access=registration }}</ref> As a system of '''enzyme nomenclature''', every EC number is associated with a recommended name for the corresponding enzyme-catalyzed reaction.

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.<ref name='expasy'>{{cite web|publisher=ExPASy |title=ENZYME (Enzyme nomenclature database) |url=http://www.expasy.org/enzyme/ |access-date=24 April 2019 |url-status=live |archive-url=https://web.archive.org/web/20190321195549/https://enzyme.expasy.org/ |archive-date=21 March 2019}}</ref> Furthermore, through [[convergent evolution]], completely different [[protein fold class|protein folds]] can catalyze an identical reaction (these are sometimes called [[non-homologous isofunctional enzymes]])<ref name="pmid20433725">{{cite journal|vauthors=Omelchenko MV, Galperin MY, Wolf YI, Koonin EV |title=Non-homologous isofunctional enzymes: a systematic analysis of alternative solutions in enzyme evolution |journal=Biology Direct |volume=5 |issue=1 |page=31 |year=2010 |pmid=20433725 |pmc=2876114 |doi=10.1186/1745-6150-5-31 |doi-access=free }}</ref>  and therefore would be assigned the same EC number. By contrast, [[UniProt]] identifiers uniquely specify a protein by its amino acid sequence.<ref name="pmid14681372">{{cite journal|vauthors=Apweiler R, Bairoch A, Wu CH, Barker WC, Boeckmann B, Ferro S, Gasteiger E, Huang H, Lopez R, Magrane M, Martin MJ, Natale DA, O'Donovan C, Redaschi N, Yeh LS |title=UniProt: the Universal Protein knowledgebase |journal=Nucleic Acids Research |volume=32 |issue=Database issue |pages=D115–9 |date=Jan 2004 |pmid=14681372 |pmc=308865 |doi=10.1093/nar/gkh131}}</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.  Preliminary EC numbers exist and have an 'n' as part of the fourth (serial) digit (e.g. EC 3.5.1.n3).<ref name="expasy"/>

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 hydrolases (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==
NB:The enzyme classification number is different from the 'FORMAT NUMBER'
{| class="wikitable"
|+ Top-level EC numbers<ref name=moss>{{cite web
| author = Moss GP
| 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.sbcs.qmul.ac.uk/iubmb/enzyme/
| archive-url = https://web.archive.org/web/20180910045839/http://www.sbcs.qmul.ac.uk/iubmb/enzyme/
| url-status = dead
| archive-date = 2018-09-10
| access-date = 2006-03-14}}</ref>
|-
! Class
! Reaction catalyzed
! Typical reaction
! Enzyme example(s) with trivial name
|-
! |[[List of EC numbers (EC 1)|EC 1]]<br />''[[Oxidoreductase]]s''
| 
[[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]]
|-
! [[List of EC numbers (EC 2)|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]]
|-
! [[List of EC numbers (EC 3)|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]], [[phosphatase]]
|-
! [[List of EC numbers (EC 4)|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> or [X-A+B-Y] → [A=B + X-Y]
| [[Decarboxylase]]
|-
! [[List of EC numbers (EC 5)|EC 5]]<br />''[[Isomerase]]s''
| Intramolecule rearrangement, i.e. [[isomer]]ization changes within a single molecule
| ABC → BCA</td>
| [[Isomerase]], [[mutase]]
|-
! [[List of EC numbers (EC 6)|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 + P<sub>i</sub>
| [[Synthetase]]
|-
! [[List of EC numbers (EC 7)|EC 7]]<br />''[[Translocase]]s''
| Catalyse the movement of ions or molecules across membranes or their separation within membranes
| 
| [[Membrane transport protein|Transporter]]
|}

==Reaction similarity==
Similarity between enzymatic reactions <!--([http://www.chem.qmul.ac.uk/iubmb/enzyme/ EC])--> can be calculated by using bond changes, reaction centres or substructure metrics (formerly <!--[http://www.ebi.ac.uk/thornton-srv/software/rbl/--> EC-BLAST], now the <!--[https://www.ebi.ac.uk/enzymeportal/,--> EMBL-EBI Enzyme Portal).<ref name="asad">{{cite journal|vauthors=Rahman SA, Cuesta SM, Furnham N, Holliday GL, Thornton JM |title=EC-BLAST: a tool to automatically search and compare enzyme reactions |journal=Nature Methods |volume=11 |issue=2 |pages=171–174 |date=Feb 2014 |pmid=24412978 |doi=10.1038/nmeth.2803 |pmc=4122987}}</ref>

==History==
Before the development of the EC number system, enzymes were named in an arbitrary fashion, and names like [[old yellow enzyme]] and [[malic enzyme]] that give little or no clue as to what reaction was catalyzed were in common use. Most of these names have fallen into disuse, though a few, especially proteolyic enzymes with very low specificity, such as [[pepsin]] and [[papain]], are still used, as rational classification on the basis of specificity has been very difficult.

By the 1950s the chaos was becoming intolerable, and after Hoffman-Ostenhof<ref>{{cite journal |year=1953|volume=14|pages=219–260|last=Hoffman-Ostenhof|first=O|title=Suggestions for a more rational classification and nomenclature of enzymes|journal=Advances in Enzymology and Related Subjects of Biochemistry|doi=10.1002/9780470122594.ch7|pmid=13057718|isbn=9780470122594}}</ref> and Dixon and Webb<ref>{{cite book| title=Enzymes|last1=Dixon|first1=M|last2=Webb|first2= E.C.|year=1958|publisher=Longmans Green|place=London|pages=183–227}}</ref> had proposed somewhat similar schemes for classifying enzyme-catalyzed reactions, the International Congress of Biochemistry in [[Brussels]] set up the Commission on Enzymes under the chairmanship of [[Malcolm Dixon (biochemist)|Malcolm Dixon]] in 1955. The first version was published in 1961, and the Enzyme Commission was dissolved at that time, though its name lives on in the term ''EC Number''. The current sixth edition, published by the [[International Union of Biochemistry and Molecular Biology]] in 1992 as the last version published as a printed book, contains 3196 different enzymes. Supplements 1-4 were published 1993–1999. Subsequent supplements have been published electronically, at the website of the Nomenclature Committee of the International Union of Biochemistry and Molecular Biology.<ref name=moss/> In August 2018, the [[IUBMB]] modified the system  by adding the top-level EC 7 category containing translocases.<ref>{{cite web|url=http://www.enzyme-database.org/news.php |title=Enzyme Nomenclature News: Translocases (EC 7): A new EC Class |last=Tipton |first=Keith |date=August 2018 |publisher=ExplorEnz: the primary source of the IUBMB enzyme list |archive-url=https://web.archive.org/web/20180910190358/http://www.enzyme-database.org/news.php |archive-date=10 September 2018 |url-status=live |access-date=3 November 2018}}</ref>

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

== References ==
{{reflist|33em}}

== External links ==
{{Wikidata property|P591}}
*[https://www.qmul.ac.uk/sbcs/iubmb/enzyme/ Enzyme Nomenclature], authoritative website by the Nomenclature Committee of the International Union of Biochemistry and Molecular Biology, maintained by G.P. Moss
*[https://enzyme.expasy.org/ Enzyme nomenclature database] &mdash; by [[ExPASy]]
*[http://www.brenda-enzymes.org/all_enzymes.php List of all EC numbers ] &mdash; by [[BRENDA]]
*[http://www.pdbe.org/ec Browse PDB structures by EC number]
*[http://supfam.org/SUPERFAMILY/cgi-bin/dcbo.cgi?type=EC;po=root Browse SCOP domains by EC number] &mdash; by [[dcGO]]
*[http://www.ebi.ac.uk/thornton-srv/software/rbl/ Compare EC numbers using EC-Blast] {{Webarchive|url=https://web.archive.org/web/20190530132101/http://www.ebi.ac.uk/thornton-srv/software/rbl/ |date=2019-05-30 }}

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