Quinolinic acid accumulation in the conversion of 3-hydroxyanthranilic acid to niacin in Neurospora.

3-Hydroxyanthranilic acid has been shown to serve as a natural precursor of niacin in Neurospora. 12 Little. information, however, has been obtained concerning the mechanism whereby the aromatic ring of 3hydroxyanthranilic acid is converted to the pyridine ring of niacin. The present paper will deal with this latter problem. Singal, et al.,I have reported that the administration of tryptophan to rats results in the urinary excretion of a compound possessing niacin activity for Lactobacillus arabinosus after autoclaving in acid solution. This compound has recently been isolated and identified by Henderson4 as quinolinic acid (2,3-dicarboxypyridine). These data suggest that quinolinic acid plays a r6le in the biosynthesis of niacin. Quinolinic acid had been tested earlier on certain mutant strains of Neurospora requiring niacin for growth, and found to be inactive.1,2 However, it seemed desirable to determine whether this compound might not be accumulated by niacin-requiring mutant strains, and have escaped attention because of its inactivity. One mutant strain has been found which accumulates this compound as a result of a genetic block. Experimenta.-The various mutant strains of Neuorspora used in this investigation, together with the compounds known to support their growth are listed in table 1. The basal medium used throughout is the customary