The enzyme aspartate transcarbamoylase (ATCase) catalyzes the first step in the pyrimidine synthesis pathway. When cytosine and uracil nucleotides are present in excess, they bind to sites outside of the active site to inhibit ATCase. This scenario illustrates ____.
A)allosteric regulation only
B)feedback inhibition only
C)a redox reaction
D)allosteric regulation and feedback inhibition
E)feedback inhibition and a cyclic pathway

Question

Quizplus · Accepted Answer

The scenario illustrates both allosteric regulation, as the binding of excess nucleotides changes the shape of the enzyme and inhibits its activity, and feedback inhibition, as the end products of the pyrimidine synthesis pathway regulate the activity of the enzyme catalyzing the first step.

The Enzyme Aspartate Transcarbamoylase (ATCase) Catalyzes the First Step in the Pyrimidine