Conversion ratio of tryptophan to niacin in rats fed with a nicotinic acid-free, tryptophan-limiting diet.

The effects of amino acid composition on the conversion ratio of Trp to niacin in rats were investigated. The ratio in the group fed with a nicotinic acid-free, 9% casein-sucrose diet (basal diet) was 3.5%. This ratio was statistically decreased to 0.2% by the addition of 2% glycine, 0.078% L-threonine, and 0.2% L-cystine, and restored to 3.2% by the further addition of 0.1% tryptophan. From these results and our previous findings, it was considered that Trp imbalance might be a manifestation of niacin deficiency.