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 small subunit active site contains an active Cys residue. CPS I contains a methylglyoxal synthetase (MGS) domain which binds ornithine.