In the urea cycle, what is the initial substrate converted into carbamoyl phosphate?

In the urea cycle, the substrate that is converted into carbamoyl phosphate is glutamate. The process begins in the mitochondria of liver cells, where ammonia (NH3), produced primarily from the deamination of amino acids, reacts with bicarbonate (HCO3-) to form carbamoyl phosphate. This reaction is catalyzed by the enzyme carbamoyl phosphate synthetase I, and it requires two molecules of ATP.

Glutamate plays a critical role in the urea cycle as it provides the nitrogen needed for the formation of carbamoyl phosphate. The conversion of ammonia into carbamoyl phosphate is a key step that prepares it for incorporation into the urea cycle, ultimately facilitating the detoxification of ammonia through the production of urea. Thus, the correct answer is linked to the essential function of glutamate in nitrogen metabolism, underscoring its importance in the urea cycle.