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
Carbamoyl phosphate synthase - 1 is stimulated by ? 
Select and explain. 
A. ATP, B. Arginosuccinate, C. Carbamoyl phosphate, D. N-acetyl glutamate
D: N-acetyl glutamate
Answer: D: N-acetyl glutamate 
Explanation: Carbamoyl phosphate synthase-I (CPS-I), a mitochondrial enzyme, catalyzes the formation of carbamoyl phosphate by condensation of CO2 and ammonia.Two molecules of ATP are required for the reaction. CPS-I is the rate limiting enzyme of urea cycle. It is an allosteric enzyme and allosterically activated by N-acetyl glutamate.