Carbamoyl phosphate synthetase

Function

Carbamoyl phosphate synthetase (CPS) catalyzes the production of carbamoyl phosphate from ATP, Mg+2, bicarbonate andglutamine. CPS is part of the pyrimidine and arginine biosynthesis as well as the urea cycle in vertebrates. Ornithine is an allosteric effector of CPS. There are 3 forms of CPS:

• CPS I participates in the urea cycle. CPS I uses glutamine for NH3 source.
  
• CPS II participates in pyrimidine metabolism
  
• CPS III is found in fish.

Disease

CPS I deficiency causes the accumulation of NH3 in the blood.

Structural highlights

CPS I and II are composed of 2 subunits. The large subunit contain active sites which bind nucleotides and other effectors. The small subunit catalyzes the hydrolysis of glutamine to glutamate and NH3. The . CPS I contains a methylglyoxal synthetase (MGS) domain which binds ornithine.