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
All of the following are derivatives of tryptophan EXCEPT: 
Select and explain. 
A. Melatonin, B. Serotonin, C. Niacin, D. Creatinine
D: Creatinine
Answer: D: Creatinine 
Explanation: Ans. (d) Creatinine* Tryptophan is one of the essential aromatic amino acid* Metabolic fate of tryptophan: Metabolized by enzyme Tryptophan oxygenase (pyrrolase)* Derivatives of tryptophan:# Niacin (Nicotinic acid)# Serotonin# Melatonin* Note: Creatinine is synthesized from 3 amino acids namely: Glycine, Arginine. Methionine