Question

Which of the following amino acids is helpful in partially meeting niacin requirement?

• A. Phenylalanine
• B. Tryptophan
• C. Tyrosine
• D. Threonine

Hint:

Nutritional Equivalents: 60 mg Tryptophan $\rightarrow$ 1 mg Niacin (Vitamin $\text{B}_3$). Corn/Maize is pellagragenic because its niacin is bound (niacytin) and it is low in tryptophan.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Endogenous vitamin biosynthesis: the essential aromatic amino acid L-tryptophan is converted via the kynurenine pathway into nicotinic acid mononucleotide (Niacin Vitamin B3).
Key Formula or Approach:
\[ 60\text{ mg Dietary L-Tryptophan} \xrightarrow{\text{Kynurenine-Quinolinate Pathway}} 1\text{ mg Niacin (Nicotinic Acid)} \]

Step 2: Detailed Explanation:
In animal and human nutrition:
- L-Tryptophan serves as a biosynthetic precursor for Niacin (Vitamin $\text{B}_3$ Nicotinamide).
- Through the hepatic kynurenine pathway (requiring vitamin $\text{B}_6$ dependent kynureninase), approximately 60 mg of dietary tryptophan generates 1 mg of niacin equivalent (1 NE).
- Therefore, diets rich in high-quality tryptophan-containing animal proteins spare and partially meet the dietary requirement for niacin.

Step 3: Final Answer:
Hence, Tryptophan is helpful in meeting niacin requirement, matching option (B).