Doc:SysName

Systematic Name of Enzymes (酵素のシステム名)

EC (Enzyme Commission) number is assigned according to the type of reaction catalysed (EC level 1) and the type(s) of the substrate(s). Since reactions are written for the purpose of classification, the direction does not reflect the actually demonstrated catalysis. The systematic name always reflects the first enzyme-catalysed step, and subsequent transformations are written in parentheses, e.g. acetyl-CoA:glyoxylate C-acetyltransferase (thioester-hydrolysing, carboxymethyl-forming) (EC 2.3.3.9).

EC class 1

In this class, a substrate is oxidized as hydrogen donor. The systematic name is donor:acceptor oxidoreductase. The common name is usually dehydrogenase, reductase (when reverse reaction is demonstrated), or oxydase (only when O₂ is the acceptor).

EC class 2

In this class, a chemical 'group' is transferred from a 'donor' to an 'acceptor'. The systematic name is donor:acceptor grouptransferase. The common name is usually acceptor grouptransferase, donor grouptransferase, or phosphorylase (when phosphate is an acceptor). Transaminase is formally considered as the combination of oxidative deamination of the donor followed by reductive amination of the acceptor, but is classified in this class (EC 2.6.1).

EC class 3

In this class, hydrolytic cleavage of C-O, C-N, C-C and some other bonds occurs. The systematic name is hydrolase. The common name is usually the substrate name with -ase. Hydrolase is formally considered as tranfer of a specific group to water as acceptor. The names of peptide hydrolases (proteinase) is based on historical priority due to their 'esterolytic' action.

EC class 4

In this class, C-C, C-O, C-N, and other bonds are cleaved by elimination, leaving double bonds or rings. The systematic name is substrate group-lyase. Major common names are decarboxylase, aldolase, and dehydratase. When reverse reaction is demonstrated, synthase (not synthetase) may be used. Pyridoxal-phosphate enzymes usually replace the eliminated substituent by some other group, and therefore, may be formally considered as alkyl-transferase.

EC class 5

In this class, geometry or structure is changed within one molecule. Common names include racemase, epimerase, (cis-trans-)isomerase, tautomerase, mutase or cycloisomerase.

EC class 6

In this class, two substrates are joined with the hydrolysis of ATP. The systematic name is X:Y ligase (ADP-forming). An obsolete common name is synthetase (not synthase).