title: NADP+ enhances cholera and pertussis toxin-catalyzed ADP-ribosylation of membrane proteins.
abstract: [32P]ADP-ribosylation of membrane proteins catalyzed by either cholera toxin or pertussis toxin was markedly enhanced by NADP+. The effect was concentration dependent; with 20 microM [32P]NAD+ as a substrate maximal enhancement was obtained at a concentration of 0.5-1.0 mM NADP+ for rabbit and guinea-pig liver membranes and 0.1 mM NADP+ for human erythrocyte membranes. NADP+ appears to act by inhibiting the degradation of NAD+ by NAD+-glycohydrolase (NADase) present in membrane preparations, probably as an alternate substrate for the enzyme. Among inhibitors tested (NADP+, isonicotinic acid hydrazide, imidazole, nicotinamide, L-arginine methyl ester and HgCl2) to suppress the enzyme activity, NADP+ was the most effective and, at 10 mM, inhibited hepatic NADase activity by about 90%. The effect of NADP+ was much greater than that of other known effectors of ADP-ribosylation such as Mg2+ and phosphate, or the NADase inhibitors, isonicotinic acid hydrazide and isonicotinamide. In membranes which contain substantial activities of NADase the inclusion of NADP+ in the assay system is necessary to achieve maximal ADP-ribosylation of membrane proteins.
mesh_terms: D000246:Adenosine Diphosphate Ribose / Q000378:metabolism*; D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D002772:Cholera Toxin / Q000494:pharmacology*; D004910:Erythrocyte Membrane / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism; D006168:Guinea Pigs; D006801:Humans; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D008627:Mercuric Chloride / Q000494:pharmacology; D009244:NAD+ Nucleosidase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009249:NADP / Q000494:pharmacology*; D037342:Pertussis Toxin; D011817:Rabbits; D010566:Virulence Factors, Bordetella / Q000494:pharmacology*
chemical_list: D008565:Membrane Proteins; D010566:Virulence Factors, Bordetella; D000246:Adenosine Diphosphate Ribose; D009249:NADP; D008627:Mercuric Chloride; D002772:Cholera Toxin; D037342:Pertussis Toxin; D009244:NAD+ Nucleosidase; D019204:GTP-Binding Proteins