This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Proteins and Amino Acids, Subject name: Biochemistry
A Carbamoyl phosphate synthetasel structure is marked by change in the presence of: 
Select and explain. 
A. N-Acetyl glutamate, B. N-Acetyl Aspartate, C. Neuraminic acid, D. Oxalate
A: N-Acetyl glutamate
Answer: A: N-Acetyl glutamate 
Explanation: Ans. A. N-Acetyl glutamateCarbamoyl phosphate synthetase I is the rate committed step of Urea cycle. It is present in the mitochondria of Liver cells. Carbamoyl phosphate synthetase II is present in the cytosol of liver and is involved in pyrimidine synthesis. Carbamoyl phosphate synthetase I is activated allosterically by NAG (N-acetyl glutamate). NAG brings about some conformational changes in the enzyme and affects the affinity of the enzyme for ATP.