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
Glutamate is NOT a precursor of: 
Select and explain. 
A. GABA, B. Proline, C. Glutathione, D. Histidine
D: Histidine
Answer: D: Histidine 
Explanation: Glutamate It is one of the most metabolically active of all amino acids. It is a precursor to: Glutamine, Arginine, Creatine phosphate, Proline, Hydroxyproline, Polyamines, Glutathione, and Gamma-aminobutyric acid (GABA). GABA, is a neurotransmitter, and is also involved in the synthesis of glutathione. In addition, glutamate itself is a neurotransmitter.