title: Azotobacter vinelandii glucose 6-phosphate dehydrogenase properties of NAD- and NADP-linked reactions.
abstract: Glucose 6-phosphate oxidation, catalyzed by purified Azotobacter vinelandii glucose 6-phosphate dehydrogenase, was studied with respect to the selective utilization of NAD, NADP, thionicotinamide adenine dinucleotide or thionicotinamide adenine dinucleotide phosphate as coenzyme. A sigmoidal relationship was observed for the effect of substrate concentration on initial velocities when either NAD, NADP or thionicotinamide adenine dinucleotide was used as coenzyme, with N values from the Hill equation equalling 2.0, 1.7, and 1.7, respectively. The thionicotinamide analogs of NAD and NADP both functioned as coenzyme-competitive inhibitors of the enzyme-catalyzed NAD- and NADP-linked reactions. A dual wavelength assay, using a combination of NADP and thio-NAD, was established and was used to demonstrate that increasing glucose 6-phosphate concentration did not change the enzyme preference for the coenzyme form used. Sigmoidal relationships were observed for reduction of both dinucleotides, and N values were the same as those observed when each dinucleotide was studied as the only coenzyme form present in reaction mixtures. Using the dual wavelength assay, inhibition by isocitrate, 6-phosphogluconate, ATP, and palmitoyl-CoA was shown to be equally effective in both NAD- and NADP-linked reactions. An enzyme activator, glucosamine 6-phosphate, altered the glucose 6-phosphate sigmoidicity through activation at low substrate concentrations.
authors.affiliation: Department of Biochemistry, Virginia Polytechnic Institute and State University, Blacksburg 20461-0308, USA. bruce@vt.edu
authors.forename: B M
authors.initials: BM
authors.lastname: Anderson
authors.forename: D J
authors.initials: DJ
authors.lastname: Wise
authors.forename: C D
authors.initials: CD
authors.lastname: Anderson
mesh_terms: D016948:Azotobacter vinelandii / Q000201:enzymology*; D005944:Glucosamine / Q000031:analogs & derivatives / Q000494:pharmacology; D019298:Glucose-6-Phosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D005954:Glucosephosphate Dehydrogenase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007700:Kinetics; D009243:NAD / Q000378:metabolism*; D009249:NADP / Q000378:metabolism*; D010171:Palmitoyl Coenzyme A / Q000494:pharmacology
chemical_list: D009243:NAD; D010171:Palmitoyl Coenzyme A; C001293:glucosamine 6-phosphate; D009249:NADP; D019298:Glucose-6-Phosphate; D005954:Glucosephosphate Dehydrogenase; D005944:Glucosamine