Carbamoyl phosphate synthetase

[1] This ATP-grasp enzyme catalyzes the reaction of ATP and bicarbonate to produce carboxy phosphate and ADP.

In turn, carbamic acid reacts with a second ATP to give carbamoyl phosphate plus ADP.

It represents the first committed step in pyrimidine and arginine biosynthesis in prokaryotes and eukaryotes, and in the urea cycle in most terrestrial vertebrates.

There are three different forms that serve very different functions: Carbamoyl phosphate synthetase has three main steps in its mechanism and is, in essence, irreversible.

[5] Carbamoyl phosphate synthase (CPSase) is a heterodimeric enzyme composed of a small and a large subunit (with the exception of CPSase III, which is composed of a single polypeptide that may have arisen from gene fusion of the glutaminase and synthetase domains).