Synthases and Ligases

From the JCBN/NC-IUB Newsletter 1984 [1]

NC-IUB have received many representations that the words 'synthase' and 'synthetase' are too similar to convey mutually exclusive meanings efficiently. We have therefore changed the usage in Enzyme Nomenclature, though in a way that allows authors who prefer the usage recommended previously to continue to follow it. The word synthase can now be added to the name of any substance to signify an enzyme that catalyses a reaction producing that substance, i.e. its range is extended to include enzymes catalysing reactions that involve hydrolysis of a nucleoside triphosphate, which previously could not be called synthases. Thus previously used names like glycogen synthase and citrate synthase are joined by the new ones glutamine synthase and NAD+ synthase.

Enzymes that catalyse synthetic reactions with concomitant hydrolysis of a nucleoside triphosphate will now contain 'ligase' rather than 'synthetase' in their Recommended Names when the two reactants that are joined are specified. Thus tyrosine-tRNA ligase and acetate-CoA ligase will replace tyrosyl-tRNA synthetase and acetyl-CoA synthetase as Recommended Names, although the synthetase forms remain acceptable.

Authors may continue to use the word synthetase to distinguish an enzyme whose reaction involves hydrolysis of a nucleoside triphosphate, but they are more likely to be understood if they use ligase, in view of the large number of biochemists who do not distinguish between the meanings of synthase and synthetase.

1. IUPAC-IUB Joint Commission on Biochemical Nomenclature (JCBN), and Nomenclature Commission of IUB (NC-IUB),.Newsletter 1984, Arch. Biochem. Biophys., 1984, 229, 237-245; Biochem. Internat., 1984, 8, following p 202; Biochem. J., 1984, 217, I-IV; Biosci. Rep., 1984, 4, 177-180; Chem. Internat., 1984(3), 24-25; Eur. J. Biochem., 1984, 138, 5-7; Hoppe-Seyler's Z. Physiol. Chem., 1984, 365, I-IV; Trends Biochem. Sci., 1984, 9, various issues.

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