title: Kinetic studies of the reduction of yeast glutathione reductase by reduced nicotinamide hypoxanthine dinucleotide phosphate.
abstract: The reduction of yeast glutathione reductase by reduced nicotinamide hypoxanthine dinucleotide phosphate (NHxDPH) has been examined by stopped-flow kinetic methods. Like reduced glutathione or NADPH, this pyridine nucleotide generates the catalytically active two-electron reduced form of the enzyme. This reductive half-reaction with NHxDPH has only one detectable kinetic step which shows saturation kinetics (Kd = 76 microM), and has a limiting rate constant of 56 s-1. Comparison of stopped-flow and steady-state turnover data indicates that the reductive half-reaction is rate-limiting in the overall catalytic reaction. No evidence was found for a preequilibrium charge-transfer complex between NHxDPH and the active site FAD, like that seen when NADPH is the electron donor.
mesh_terms: D002384:Catalysis; D005980:Glutathione Reductase / Q000378:metabolism*; D007700:Kinetics; D009243:NAD / Q000031:analogs & derivatives* / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D013053:Spectrophotometry
chemical_list: D009243:NAD; C032140:nicotinamide-hypoxanthine dinucleotide; D009249:NADP; D005980:Glutathione Reductase