This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Tryptophan metabolism detail, Subject name: Biochemistry
Limiting amino acid in maize: 
Select and explain. 
A. Niacin, B. Tyrosine, C. Tryptophan, D. Methionine
C: Tryptophan
Answer: C: Tryptophan 
Explanation: Maize protein Zein lacks tryptophan. As tryptophan is required for the synthesis of Niacin (60 mg of tryptophan is required to make 1 mg of niacin) Hence, In high corn diet, requirement of dietary niacin increases.