IUBMB Enzyme Nomenclature


Accepted name: carbamoyl-phosphate synthase (ammonia)

Reaction: 2 ATP + NH3 + hydrogencarbonate = 2 ADP + phosphate + carbamoyl phosphate (overall reaction)
(1a) ATP + hydrogencarbonate = ADP + carboxyphosphate
(1b) NH3 + carboxyphosphate = carbamate + phosphate
(1c) ATP + carbamate = ADP + carbamoyl phosphate

For diagram click here.

Other name(s): carbon-dioxide—ammonia ligase; carbamoylphosphate synthase; carbamylphosphate synthetase; carbamoylphosphate synthase (ammonia); carbamoylphosphate synthetase; carbamylphosphate synthetase I; CPSI (gene name); carbon-dioxide:ammonia ligase (ADP-forming, carbamate-phosphorylating)

Systematic name: hydrogencarbonate:ammonia ligase (ADP-forming, carbamate-phosphorylating)

Comments: The enzyme catalyses the first committed step in the urea cycle. The reaction proceeds via three separate chemical reactions: phosphorylation of hydrogencarbonate to carboxyphosphate; a nucleophilic attack of ammonia on carboxyphosphate yielding carbamate; and the phosphorylation of carbamate forming carbamoyl phosphate. Two moles of ATP are utilized for the synthesis of one molecule of carbamyl phosphate, making the reaction essentially irreversible. The enzyme requires the allosteric activator N-acetyl-L-glutamate. cf. EC, carbamoyl-phosphate synthase (glutamine-hydrolysing).

Links to other databases: BRENDA, EXPASY, KEGG, Metacyc, PDB, CAS registry number: 9026-23-7


1. Fahien, L.A. and Cohen, P.P. A kinetic study of carbamyl phosphate synthetase. J. Biol. Chem. 239 (1964) 1925-1934.

2. Jones, M.E. and Spector, L. The pathway of carbonate in the biosynthesis of carbamyl phosphate. J. Biol. Chem. 235 (1960) 2897-2901.

3. Marshall, M., Metzenberg, R.L. and Cohen, P.P. Purification of carbamyl phosphate synthetase from frog liver. J. Biol. Chem. 233 (1958) 102-105.

4. Marshall, M., Metzenberg, R.L. and Cohen, P.P. Physical and kinetic properties of carbamyl phosphate synthetase from frog liver. J. Biol. Chem. 236 (1961) 2229-2237.

[EC created 1965 as EC, transferred 1978 to EC]

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