Carbamoyl-phosphate_synthase_(glutamine-hydrolysing)
Carbamoyl phosphate synthase II
Enzyme
Carbamoyl phosphate synthetase (glutamine-hydrolysing) (EC 6.3.5.5) is an enzyme that catalyzes the reactions that produce carbamoyl phosphate in the cytosol (as opposed to type I, which functions in the mitochondria). Its systemic name is hydrogen-carbonate:L-glutamine amido-ligase (ADP-forming, carbamate-phosphorylating).[1][2][3][4][5][6][7][8]
In pyrimidine biosynthesis, it serves as the rate-limiting enzyme and catalyzes the following reaction:
- 2 ATP + L-glutamine + HCO3− + H2O 2 ADP + phosphate + L-glutamate + carbamoyl phosphate (overall reaction)
- (1a) L-glutamine + H2O L-glutamate + NH3
- (1b) 2 ATP + HCO3− + NH3 2 ADP + phosphate + carbamoyl phosphate
It is activated by ATP and PRPP[9] and it is inhibited by UTP (Uridine triphosphate)[10] Neither CPSI nor CPSII require biotin as a coenzyme, as seen with most carboxylation reactions.
It is one of the three enzyme functions coded by the CAD gene. It is classified under EC 6.3.5.5.