EC - Carbamoyl-phosphate synthase (ammonia)

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IntEnz Enzyme Nomenclature


Accepted name:
carbamoyl-phosphate synthase (ammonia)
Other names:
carbamoylphosphate synthase
carbamoylphosphate synthase (ammonia)
carbamylphosphate synthetase
carbamylphosphate synthetase I
carbmoylphosphate synthetase
carbon-dioxide—ammonia ligase
carbamoyl-phosphate synthetase I
carbamoyl-phosphate synthetase (ammonia)
carbamoylphosphate synthetase (ammonia)
CPSI (gene name)
Systematic name:
HCO3:ammonia ligase (ADP-forming, carbamate-phosphorylating)



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). Formerly EC

Links to other databases

Enzymes and pathways: NC-IUBMB , BRENDA , DIAGRAM , ExplorEnz , ENZYME@ExPASy , KEGG , MetaCyc , UniPathway
Protein domains and families: PROSITE:PDOC00676
Structural data: CSA , EC2PDB
Gene Ontology: GO:0004087
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 : 1925-1934 (1964). [PMID: 14213379]
  2. Jones, M.E. and Spector, L.
    The pathway of carbonate in the biosynthesis of carbamyl phosphate.
    J. Biol. Chem. 235 : 2897-2901 (1960). [PMID: 13790558]
  3. Marshall, M., Metzenberg, R.L. and Cohen, P.P.
    Purification of carbamyl phosphate synthetase from frog liver.
    J. Biol. Chem. 233 : 102-105 (1958). [PMID: 13563449]
  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 : 2229-2237 (1961).
  5. Pierson, D. L., Brien, J. M.
    Human carbamylphosphate synthetase I. Stabilization, purification, and partial characterization of the enzyme from human liver.
    J. Biol. Chem. 255 : 7891-7895 (1980). [PMID: 6249820]
  6. Pekkala, S., Martinez, A. I., Barcelona, B., Gallego, J., Bendala, E., Yefimenko, I., Rubio, V., Cervera, J.
    Structural insight on the control of urea synthesis: identification of the binding site for N-acetyl-L-glutamate, the essential allosteric activator of mitochondrial carbamoyl phosphate synthetase.
    Biochem. J. 424 : 211-220 (2009). [PMID: 19754428]

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