Kinetic studies of the reduction of yeast glutathione reductase by reduced nicotinamide hypoxanthine dinucleotide phosphate.
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.
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
D009243:NAD; C032140:nicotinamide-hypoxanthine dinucleotide; D009249:NADP; D005980:Glutathione Reductase