Nicotinate Phosphoribosyltransferase Research Articles

Inhibition of Nicotinate Phosphoribosyl Transferase by Nonsteroidal Anti-Inflammatory Drugs: A Possible Mechanism of Action

When incubated with 14C-nicotinic acid and phosphorylribose-1-pyrophosphate, human platelet lysate incorporates radioactivity into nicotinic acid mononucleotide. Under these conditions, the apparent Km of nicotinic acid for nicotinate phosphoribosyl transferase is 2.4 × 10−5M. Along with 2-hydroxynicotinic acid (Ki = 2.3 × 10−4M), the following nonsteroidal anti-inflammatory compounds competed reversibly with nicotinic acid for the enzyme: flufenamic acid (Ki = 4.6 × 10−5M), mefenamic acid (Ki = 7.6 × 10−5M), salicylic acid (Ki = 1.6 × 10−4M), phenylbutazone (Ki = 1.6 × 10−4M), and indomethacin (Ki = 4.2 × 10−4M). Such inhibition may explain the decreases in nicotinamide adenine dinucleotide phosphate content of rat liver after administration of salicylate. Furthermore, suppression of nicotinamide adenine dinucleotide biosynthesis by anti-inflammatory drugs may restrain mucopolysaccharide biosynthesis and, thereby, reduce inflammatory responsiveness. Hence, this antagonism of niacin may be involved in the pharmacologic activity and, particularly, the toxicity of anti-inflammatory drugs.

Inhibition of nicotinate phosphoribosyltransferase in human platelet lysate by nicotinic acid analogs

Inhibition of nicotinate phosphoribosyltransferase in human platelet lysate by nicotinic acid analogs

Nicotinate Phosphoribosyltransferase of Yeast: PURIFICATION AND PROPERTIES

Abstract Nicotinate phosphoribosyltransferase from bakers' yeast has been purified about 1,000-fold; the purified material showed only one band on cellulose acetate electrophoresis (pH 5.0 and 8.6). In addition to 5-phosphoribosyl 1-pyrophosphate, adenosine triphosphate (ATP) or an analogous nucleotide is required for enzyme activity and the stoichiometric hydrolysis of ATP to adenosine diphosphate (ADP) and orthophosphate with formation of products, nicotinic acid mononucleotide and pyrophosphate, was verified with this purified preparation. The nucleotide specificity, however, is broader than that of the liver form of this enzyme. The molecular weight of the yeast enzyme was estimated from Sephadex chromatography to be 43,000 (about one-half that of the liver enzyme) whether in the presence or absence of ATP. Phosphate ions greatly stimulate the enzyme activity, giving optimum activity in the range of 10 to 100 mm phosphate in the presence of 5 mm Mg++. At 1 and 5 mm Mg++, optimum enzyme activities are observed with equimolar concentration of ATP. The enzyme catalyzes isotope exchange between ATP and ADP at rates approximately 8 times its molecular activity with all substrates, although no net ATP hydrolysis occurs in the absence of other substrates. ATP, guanosine triphosphate, and the substrates, nicotinic acid and 5-phosphoribosyl 1-pyrophosphate, protect the enzyme from heat inactivation.

Allosteric Properties of Bovine Liver Nicotinate Phosphoribosyltransferase

Abstract Nicotinate phosphoribosyltransferase has been partially purified from bovine liver and some of its kinetic properties studied. This enzyme is easily separable from niacin ribonucleotidase. ATP is not a required substrate for bovine liver nicotinate phosphoribosyltransferase, as has been reported, but activates the enzyme by lowering the apparent Michaelis constants for both nicotinate and ribosylpyrophosphate 5-phosphate by approximately 10-fold. The stimulation by ATP appears to be highly specific. The kinetics of ATP activation indicate that ATP is binding at only one site on the enzyme. When ATP is present in the reaction, it is cleaved to form ADP in an amount approximately stoichiometric with nicotinic acid mononucleotide formation. It is suggested that ATP cleavage may be required for the activation of the enzyme.

A comparative study of the regulation of nicotinamide-adenine dinucleotide biosynthesis

1. 1. The regulation of NAD biosynthesis was studied in Escherichia coli, Bacillus subtilis and Bacillus megaterium, bacteria which utilize conventional metabolites and an “aspartate-glycerol pathway” for NAD biosynthesis and Xanthomonas pruni, the only bacterium in which tryptophan is known to serve as a precursor to NAD. The recent findings that in bacteria quinolinic acid occurs via the aspartate-glycerol pathway, suggested the need for a more recent evaluation. 2. 2. The biosynthesis of quinolinic acid via the aspartate-glycerol pathway in E. coli is repressed when cells are grown in the presence of excessive levels of nicotinic acid. In addition, nicotinate phosphoribosyltransferase (EC 2.4.2.11), an enzyme on the ‘salvage pathway’ for NAD biosynthesis, is repressed by comparable levels of nicotinic acid. However, quinolinate phosphoribosyltransferase is unaffected under the same conditions of growth. In contrast, in B. subtilis and B. megaterium quinolinate phosphoribosyltransferase is repressed by growth on increased levels of nicotinic acid, but nicotinate phosphoribosyltransferase is not. 3. 3. None of the enzymes of the tryptophan-NAD pathway studied in Xanthomonas pruni was repressed by growth in the presence of excess nicotinic acid. However, feedback inhibition of tryptophan pyrrolase may offer a means for the regulation of NAD biosynthesis in this organism.