Which one of the following occurs in the urea cycle?
Carbamoyl phosphate within the mitochondria is formed from NH4+ ,CO2 , and ATP. Carbamoyl phosphate synthetase II catalyzes carbamoyl phosphate synthesis from glutamine for pyrimidine synthesis in the cytoplasm. Carbamoyl phosphate reacts with ornithine to form citrulline, which reacts with aspartate to form argininosuccinate. Fumarate is released from argininosuccinate, and arginine is formed. Urea is produced from the guanidinium group on the side chain of arginine, not from the amino group on the a-carbon. Ornithine is regenerated. N-Acetylglutamate is an allosteric activator of carbamoyl phosphate synthetase I. Ornithine transcarbamylase is not a regulated enzyme in mammals, and in bacteria, N-acetylglutamate is not an allosteric effector of ornithine transcarbamylase.
Carbamoyl phosphate is derived directly from glutamine and CO2.
Ornithine reacts with aspartate to generate argininosuccinate.
The a-amino group of arginine forms one of the nitrogens of urea.
Ornithine directly reacts with carbamoyl phosphate to form citrulline.
Proteins and Amino Acids