ABSTRACT
By comparing chemical composition of jowar and maize, Gopalan and Srikantia noticed that both cereals contain high levels of leucine and they conducted several experiments on the effects of dietary excessive leucine. Human subjects and rats maintained on a high-leucine diet excreted significantly more quinolinic acid and N^methylnicotinamide in urine. The absorption of leucine from the digestive tract certainly competes with that of tryptophan at a limited area of brush borders. However, it is not to be expected that tryptophan is excreted in feces wastefully without being absorbed because of the local competition for absorption between the two amino acids. If leucine competes with tryptophan and is absorbed preferentially, then tryptophan will be absorbed even faster at the lower part of the small intestine where less leucine remains to be absorbed. Though causative effects of leucine were mostly focused on activities of enzymes, which catalyze metabolism of tryptophan to NAD, Kubota et al.
