a phosphotransferase catalyzing the formation of carbamoyl phosphate. There are two significant isozymes. Carbomoyl phosphate synthetase I is a mitochondrial enzyme that catalyzes the reaction of 2ATP, NH3, CO2, and H2O to carbamoyl phosphate, 2ADP, and orthophosphate. It is activated by N-acetylglutamate and participates in urea biosynthesis. A deficiency of carbamoyl phosphate synthetase I can result in hyperammonemia. Carbamoyl phosphate synthetase II is a cytosolic enzyme that, under physiological conditions, uses l-glutamine as the nitrogen source (producing l-glutamate) instead of NH3, is not activated by N-acetylglutamate, and participates in pyrimidine biosynthesis.