Nicotinamide riboside phosphorylase

The separation of phosphohydrox5dmino acids by h.p.l.c. has been described. A very sensitive method for the determination of inorganic phosphate has been described which is based on the formation of a Rhodamine B-phosphomolybdate complex, and the continuous enzsmiic removal of inorganic phosphate from reactions has been achieved by means of the nucleoside phosphorylase-catalysed phosphorolysis of nicotinamide riboside, when the product is ribose 1 -phosphate. ... 

Pyridine Nucleotides. Nucleoside phosphorylase is capable of using the base nicotinamide. The product of the reaction of this base with ribose-l-phosphate is nicotinamide riboside. The formation of the corresponding nicotinamide mononucleotide is catalyzed by a typical kinase, using ATP. A specific enzyme purified from human erythrocytes has been shown to form nicotinamide mononucleotide by a second mechanism in which PRPP and nicotinamide react to form inorganic pyrophosphate and... 

The fact that nuclei do contain enzymes likely to be involved in nucleoside metabolism (nucleoside phosphorylase, adenosine deaminase, and guanase), together with the fact that nucleoside phosphorylase catalyzes the formation of nicotinamide ribosides, leads the authors to point out the possible role of the nucleus in controlling the formation of di- and triphos-phopyridine nucleotide coenzymes. 

Nicotinic Add Metabolism. The sequence of reactions leading to the formation of pyridine compounds is of particular interest as a source of nicotinic acid. Nutritional, isotopic, and genetic experiments have all shown that tryptophan and its metabolic derivatives including 3-hydroxy-anthranilic acid are precursors of nicotinic acid in animals and in Neuro-spora. The terminal steps in this sequence are not known. Under certain physiological conditions an increase in picolinic carboxylase appears to reduce nicotinic acid synthesis. This implies a common pathway as far as the oxidation of 3-hydroxyanthranilic acid. Whether quinolinic acid is a precursor of nicotinic acid is still uncertain. The enzyme that forms the amide of nicotinic acid also has not been isolated. Subsequent reactions of nicotinamide include the formation of the riboside with nucleoside phosphorylase and methylation by nicotinamide methyl-kinase. In animals W-methylnicotinamide is oxidized to the corresponding 6-pyridone by a liver flavoprotein. Nicotinic acid also forms glycine and ornithine conjugates. Both aerobic and anaerobic bacteria have been found to oxidize nicotinic acid in the 6-position. ... 

---