This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Control of urea cycle involves the enzyme: 
Select and explain. 
A. Carbamoyl phosphate synthetase, B. Ornithine transcarbamoylase, C. Argininosuccinase, D. Arginase
A: Carbamoyl phosphate synthetase
Answer: A: Carbamoyl phosphate synthetase 
Explanation: CPS-I reaction is the rate-limiting step in urea formation. It is irreversible and allosterically regulated.
Reference: Vasudevan 7th  ed, pg 203