KEGG ENZYME: 6.3.5.5 (2025)

EC6.3.5.5Enzyme


Ligases;
Forming carbon-nitrogen bonds;
Carbon-nitrogen ligases with glutamine as amido-N-donor

hydrogencarbonate:L-glutamine amido-ligase (ADP-forming, carbamate-phosphorylating)

2 ATP + L-glutamine + hydrogencarbonate + H2O = 2 ADP + phosphate + L-glutamate + carbamoyl phosphate (overall reaction) [RN:R00575];
(1a) L-glutamine + H2O = L-glutamate + NH3 [RN:R00256];
(1b) ATP + hydrogencarbonate = ADP + carboxyphosphate [RN:R10948];
(1c) NH3 + carboxyphosphate = carbamate + phosphate [RN:R10949];
(1d) ATP + carbamate = ADP + carbamoyl phosphate [RN:R01395]

The product carbamoyl phosphate is an intermediate in the biosynthesis of arginine and the pyrimidine nucleotides [4]. The enzyme from Escherichia coli has three separate active sites, which are connected by a molecular tunnel that is almost 100 A in length [8]. The amidotransferase domain within the small subunit of the enzyme hydrolyses glutamine to ammonia via a thioester intermediate. The ammonia migrates through the interior of the protein, where it reacts with carboxyphosphate to produce the carbamate intermediate. The carboxyphosphate intermediate is formed by the phosphorylation of hydrogencarbonate by ATP at a site contained within the N-terminal half of the large subunit. The carbamate intermediate is transported through the interior of the protein to a second site within the C-terminal half of the large subunit, where it is phosphorylated by another ATP to yield the final product, carbamoyl phosphate [6]. cf. EC 6.3.4.16, carbamoyl-phosphate synthase (ammonia).

EC 6.3.5.5 created 1972 as EC 2.7.2.9, transferred 1978 to EC 6.3.5.5, modified 2006