CONVERSION RATIO OF TRYPTOPHAN TO NIACIN IN RATS FED A VITAMIN-B-1-FREE DIET

The effect of a vitamin B-1-free diet on the conversion ratio of trypt ophan to niacin in rats was investigated using the current methods for determination of the intermediate metabolites. Rats were fed with die ts with or without B-1 for 33 days. The body weight gain and food inta ke in the B-1-free group were almost the same as the control group for 10 days, but, they steeply dropped after that time and the conversion ratio of tryptophan to niacin began to increase. The ratio reached 7- fold that of the control group on the last day of the experiment. This finding seriously differed from the previous reports, which described that B, was needed in the first part of tryptophan conversion to niac in and that the conversion ratio of tryptophan to niacin decreased in B-1-deficient rats. Furthermore, the activity of tryptophan oxygenase, in which it was reported that B-1 is required for the tryptophan cata lytic reaction, did not decrease but increased even when the B-1-free diet was fed. These results suggest that there is a very small possibi lity of the direct involvement of B-1 in the conversion of tryptophan to niacin.