Pyridine nucleotide synthesis in human blood--effect of leucine, alpha-ketoisocaproic acid and ketone bodies.

The effects of L-leucine and its metabolites on pyridine nucleotide synthesis were investigated in human blood. After 30 min-incubation 40% of the added (carboxyl-14C)-nicotinic acid was incorporated into pyridine nucleotides, most of which was nicotinic acid mononucleotide. Leucine and alpha-ketoisocaproic acid reduced pyridine nucleotide synthesis by 40% and 15%, respectively at 1 mM level. Ketone bodies were without effect. The results were different from those observed in rat hepatocytes [O. Yamada et al.: Internat. J. Vitam. Nutr. Res. 53, 184 (1983)], in which ketone bodies and the compounds metabolized to ketone bodies were inhibitory to the NAD biosynthesis.