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

Multiple Choice

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