5. The de novo biosynthesis of pyrimidines begin with the formation of carbamoyl phosphate Carbamoyl phosphate is formed from GIn, HCO3 and atp in a reaction catalyzed by the carbamoyl phosphate synthetase II(氨甲酰磷酸合成酶I) In the committing step of pyrimidine biosynthesis carbamoyl phosphate condenses with Asp to form N-carbamoylaspartate in a reaction catalyzed by aspartate transcarbamoylase( ATCase天冬氨酸转 氨甲酰酶)5. The de novo biosynthesis of pyrimidines begin with the formation of carbamoyl phosphate • Carbamoyl phosphate is formed from Gln, HCO3 - , and ATP in a reaction catalyzed by the carbamoyl phosphate synthetase II（氨甲酰磷酸合成酶II ）. • In the committing step of pyrimidine biosynthesis, carbamoyl phosphate condenses with Asp to form N-carbamoylaspartate in a reaction catalyzed by aspartate transcarbamoylase (ATCase 天冬氨酸转 氨甲酰酶)