This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of protein and amino acid, Subject name: Biochemistry
Glutamate is not a precursor of 
Select and explain. 
A. Ammonia, B. Proline, C. Glutathione, D. Histidine
D: Histidine
Answer: D: Histidine 
Explanation: Glutamate is formed from histidine and not vice versa. Pg no.244.proline can be synthesized from glutamate with minor modification of catabolic pathway. Also glutamate is formed from proline. Pg no.201. Fig 15.7. ammonia pool is formed from glutamate also. Pg no.199.fig 15.3.Meister cycle. Glutamate is formed from glutathione and vice versa. It&;s a cycle.Ref: DM Vasudevan - Textbook of Biochemistry for Medical Students, 7th edition, page no: 243, fig; 18.13