THE CONVERSION OF L- AND D-TRYPTOPHAN TO NIACIN IN HUMAN BODY

In order to study the conversion of tryptophan to niacin, the daily urinary excretions of niacin, N-MNA and 6-pyridone were determined of a subject ingesting the experimental diet and their changes were estimated after adding 2g of L-tryptophan, 2g of D-tryptophan and 50mg of niacinamide, respectively, in succession after 4-5 days'interval. The following results were thus obtained: (1) The administration of L-tryptophan raised the urinary excretion of niacin derivatives markedly during the first day, decreasing then gradually from the next day in the order of niacin, N-MNA and 6-pyridone. (2) D-Tryptophan was also converted into niacin though somewhat slower in rate. Maximum excretion of niacin derivatives was observed on the second day after its administration.