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
The following metabolite is a derivative of tryptophan 
Select and explain. 
A. Melatonin, B. Thyroxine, C. Epinephrine, D. Nor epinephrine
A: Melatonin
Answer: A: Melatonin 
Explanation: Tryptophan is conveed to Seratonin, which is then acetylated and fuher methylated to form Metatonin.Ref: DM Vasudevan - Textbook of Biochemistry, 7th edition, page no: 240, Fig no 18.10.