Which Enzyme of the Pyrimidine Synthesis Pathway is the Most

Question

Which enzyme of the pyrimidine synthesis pathway is the most highly regulated?
A)carbamoyl phosphate synthetase
B)aspartate transcarbamoylase
C)orotate phosphoribosyltransferase
D)UMP kinase
E)nucleoside diphosphate kinase

Accepted Answer

Aspartate transcarbamoylase is the most highly regulated enzyme in the pyrimidine synthesis pathway. It is allosterically regulated by UTP and ATP, which act as feedback inhibitors, and activated by PRPP. Carbamoyl phosphate synthetase is also regulated but to a lesser extent, while orotate phosphoribosyltransferase and UMP kinase are not as tightly regulated. Nucleoside diphosphate kinase is not directly involved in the pyrimidine synthesis pathway.