title: Hydrolysis of nicotinamide adenine dinucleotide by choleragen and its A protomer: possible role in the activation of adenylate cyclase.
abstract: Choleragen and the isolated A protomer catalyzed the hydrolysis of NAD to ADP-ribose and nicotinamide. The protein with NADase activity (NAD nucleosidase; NAD glycohydrolase, EC 3-2-2-5) migrated on polyacrylamide gels with choleragen, and chromatographed on Bio-Gel P-60 columns with the A protomer. The NADase activity of choleragen and of the A protomer was increased markedly in acetate and phosphate buffers, and enhanced over 10-fold by dithiothreitol in high concentration. NAD hydrolysis was proportional to choleragen concentration; the Michaelis constant for NAD was about 4 mM with both choleragen and the A protomer. The demonstration that the A protomer of choleragen catalyzes an enzymatic reaction involving activation of the ribosyl-nicotinamide bond of NAD, a reaction analogols to those catalyzed by diphtheria toxin, supports the hypothesis that activation of adenylate cyclase by choleragen involves the ADP-ribosylation of an appropriate acceptor protein.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D001427:Bacterial Toxins / Q000378:metabolism*; D004229:Dithiothreitol / Q000494:pharmacology; D004789:Enzyme Activation; D007700:Kinetics; D009243:NAD / Q000378:metabolism; D009244:NAD+ Nucleosidase / Q000378:metabolism*; D013329:Structure-Activity Relationship; D014734:Vibrio cholerae
chemical_list: D001427:Bacterial Toxins; D009243:NAD; D009244:NAD+ Nucleosidase; D000262:Adenylyl Cyclases; D004229:Dithiothreitol