Pyridinium Precursors of Pyridine Nucleotides in Perfused Rat Kidney and in the Testis

Nicotinic acid, at a concentration of 2.5 µ m , was a more effective precursor of NAD than was nicotinamide in perfused rat kidney. NAD synthesis from nicotinic acid occurs via nicotinic acid ribonucleotide and desamido-NAD. Nicotinamide deamidase was not active but the nicotinamide, released by NAD glycohydrolase action or added to the perfusate, was incorporated into NAD via NMN. Mono- and dinucleotides as well as quinolinate entered the kidney cells slowly. The latter was converted to nicotinic acid ribonucleotide and thence to NAD. Nicotinic acid ribonucleoside served as a precursor of NAD. Urinary products from nicotinic acid included nicotinic acid, nicotinuric acid, nicotinamide, and a trace of 6-hydroxynicotinic acid. From nicotinamide no products other than the unchanged amide were detected. Nicotinamide was the preferred precursor of NAD in the testis as shown by intratesticular injection in the whole animal or by homogenate experiments. Quinolinic acid did not serve as a source of the pyridine moiety of NAD in the testis.