NIACIN METABOLISM IN MYCOBACTERIA:Quinolinic Acid as a Precursor of Niacin Ribonucleotide and the Difference in Niacin Biosynthesis among Various Species of Mycobacteria

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Niacin biosynthesis of various species of mycobacteria was studied with cell-free extract. 3-Hydroxyanthranilic acid was not decomposed and was not utilized by mycobacteria and trypt phan pathway was excluded in mycobacteria.<BR>In mycobacteria, quinolinic acid was converted to niacin ribonucleotide in the presence of 5-phosphoribosy1-1-pyrophate. Free niacin was excluded as an intermediate of the pathway and quinolinic acid was established as an intermediate in the biosynthesis of nicotinamide adenine dinucleotide in mycobacteria. Among mycobacteria, human tubercle bacilli revealed remarkably high quinolinate transphosphoribosylase activity which converts quinolinic acid to niacin ribonu cleotide. The enzyme activity of human tubercle bacilli was 9 to 20 times more than other mycobacteria except twice of BCG. The enzyme activity was parallel to the niacin production of mycobacteria in the culture media.