Studies on pyridine nucleotide biosynthesis

Abstract

Saccharomyces cerevisiae when grown in the presence of either nicotinic acid or nicotinamide accumulates free nicotinic acid as the chief end product. N[image]-Methylnicotinamide and nicotinuric acid are not formed. Resting cells of S. cerevisiae as well as a cell-free extract have nicotinamide-deamidase activity. Cells of Leuconostoc mesenteroides 9135 are devoid of the deamidase. S. cerevisiae can synthesize diphosphophyridine nucleotide from nicotinamide as well as from nicotinic acid and can rapidly deamidate nicotinamide under both growing and resting conditions. Cells of L. mesenteroides form diphos-phopyridine nucleotide from nicotinic acid but not from nicotinamide. Experiments with [14C]nicotinic acid and [14C]nicotinamide confirm that the biosynthesis of diphosphopyridine nucleotide is effected by suspensions of S. cerevisiae almost as efficiently from nicotinamide as from nicotinamide as from nicotinic acid and that there is a rapid deamidation of nicotinamide. It is concluded that the nicotinic acid pathway of biosynthesis of diphosphopyridine nucleotide is the predominant mechanism under normal conditions in L. mesenteroides and S. cerevisiae.