Question

ATCase is an important enzyme in DNA replication. a) What does this enzyme do and what are its substrates? b) This enzyme demonstrates feedback regulation. Describe its quaternary structure in this regard. c) Besides substrate(s) and product, what other molecules are involved in the feedback regulation of ATCase? Describe their function and how they interact?

Answer 1

1 Aspartate transcarbomylase is involved in pyrimidine biosynthesis. It catalyzes the first step of the condensation reaction. Its substrates are aspartate and carbomyl phosphate and products are carbamyl aspartate.

b Its structure consists of 12 subunits. Two catalytic trimers and three regulatory dimers. Two catalytic trimers is holoenzyme which is held together by three regulatory dimers. Regulatory dimers involved in regulating activity.

C other than substrates and products, end product of this biosynthetic pathway involved in regulation. High CTP concentrations blocks the pathway by inhibiting the enzyme. Low levels of CTP increases the enzyme activity. This regulatory phenomena is regulated by binding and non-binding of CTP. High levels tend to binding and low levels tend to non-binding. Thereby regulates the pathway and this enzyme involved step is rate limiting step.