Studies of the metabolism of tryptophan labeled with N15 in the indole ring.

Recent interest in tryptophan metabolism has been stimulated by evidence that tryptophan is a precursor of nicotinic acid in mammals (1) as well as in Neurospora CTUSSU (2). The formation of kynurenine, kynurenic acid, and xanthurenic acid from tryptophan has been demonstrated by numerous experiments (3-5) and has been confirmed by isotope technique in the case of kynurenine and kynurenic acid (6). Recently it has been shown that indole plus se&e can act as a ‘precursor of tryptophan in N. CTUSSQ, and there are indications that the same relationship may hold true for certain bacteria (7). In order to study these and other aspects of tryptophan and indole metabolism, indole labeled with N16 and tryptophan labeled with N15 in the indole ring were synthesized.