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Enzyme Commission number

Chemical numbering scheme

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 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. Furthermore, through convergent evolution, completely different protein folds can catalyze an identical reaction (these are sometimes called non-homologous isofunctional enzymes) and therefore would be assigned the same EC number. By contrast, UniProt identifiers uniquely specify a protein by its amino acid sequence.

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).

For example, the tripeptide aminopeptidases 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 bonds
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	Reaction catalyzed	Typical reaction
Oxidoreductases	EC 2
Transferases	EC 3
Hydrolases	EC 4
Lyases	EC 5
Isomerases	EC 6
Ligases	EC 7
Translocases
	AH + B → A + BH (reduced)
A + O → AO (oxidized)	Dehydrogenase, oxidase
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
Formation of two products from a substrate by hydrolysis	AB + H2O → AOH + BH	Lipase, amylase, peptidase, phosphatase
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 or [X-A+B-Y] → [A=B + X-Y]	Decarboxylase
Intramolecule rearrangement, i.e. isomerization changes within a single molecule	ABC → BCA	Isomerase, mutase
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
Catalyse the movement of ions or molecules across membranes or their separation within membranes		Transporter

Reaction similarity

Similarity between enzymatic reactions can be calculated by using bond changes, reaction centres or substructure metrics (formerly ), now the EMBL-EBI Enzyme Portal).

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 proteolytic 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 and Dixon and Webb 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 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.

References

Webb, E. C.. (1992). "Enzyme nomenclature 1992: recommendations of the Nomenclature Committee of the International Union of Biochemistry and Molecular Biology on the nomenclature and classification of enzymes". Academic Press.
"ENZYME (Enzyme nomenclature database)". ExPASy.
(2010). "Non-homologous isofunctional enzymes: a systematic analysis of alternative solutions in enzyme evolution". Biology Direct.
(Jan 2004). "UniProt: the Universal Protein knowledgebase". Nucleic Acids Research.
(Feb 2014). "EC-BLAST: a tool to automatically search and compare enzyme reactions". Nature Methods.
Hoffman-Ostenhof, O. (1953). "Advances in Enzymology and Related Areas of Molecular Biology". .
(1958). "Enzymes". Longmans Green.
Tipton, Keith. (August 2018). "Enzyme Nomenclature News: Translocases (EC 7): A new EC Class". ExplorEnz: the primary source of the IUBMB enzyme list.

Info: Wikipedia Source

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