IUBMB Enzyme Nomenclature


Accepted name: cobyrinate a,c-diamide synthase

Reaction: 2 ATP + cobyrinate + 2 L-glutamine + 2 H2O = 2 ADP + 2 phosphate + cobyrinate a,c-diamide + 2 L-glutamate
(1a) ATP + cobyrinate + L-glutamine + H2O = ADP + phosphate + cobyrinate c-monamide + L-glutamate
(1b) ATP + cobyrinate c-monamide + L-glutamine + H2O = ADP + phosphate + cobyrinate a,c-diamide + L-glutamate

For diagram click here.

Other name(s): cobyrinic acid a,c-diamide synthetase; CbiA (gene name)

Comments: This enzyme is the first glutamine amidotransferase that participates in the anaerobic (early cobalt insertion) biosynthetic pathway of adenosylcobalamin, and catalyses the ATP-dependent synthesis of cobyrinate a,c-diamide from cobyrinate using either L-glutamine or ammonia as the nitrogen source. It is proposed that the enzyme first catalyses the amidation of the c-carboxylate, and then the intermediate is released into solution and binds to the same catalytic site for the amidation of the a-carboxylate. The Km for ammonia is substantially higher than that for L-glutamine. The equivalent reaction in the aerobic cobalamin biosynthesis pathway is catalysed by EC, hydrogenobyrinic acid a,c-diamide synthase (glutamine-hydrolysing).

Links to other databases: BRENDA, EXPASY, KEGG, Metacyc, CAS registry number:


1. Fresquet, V., Williams, L. and Raushel, F.M. Mechanism of cobyrinic acid a,c-diamide synthetase from Salmonella typhimurium LT2. Biochemistry 43 (2004) 10619-10627. [PMID: 15311923]

[EC created 2010]

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