NADPH oxidation catalyzed by the peroxidase/H2O2 system. Guaiacol-mediated and scopoletin-mediated oxidation of NADPH to NADPH+.
We have examined the respective roles played by guaiacol and scopoletin in NADPH oxidation catalyzed by the peroxidase/H2O2 system. It was shown that NADPH was not oxidized by either the horseradish or lactoperoxidase/H2O2 systems alone; oxidation occurred immediately after the addition of guaiacol or scopoletin. In both cases, the oxidation product was enzymatically active NADP+. Differences were observed in the NADPH oxidation mechanism depending on whether guaiacol or scopoletin was the mediator molecule. In guaiacol-mediated NADPH oxidation, the stoichiometry between H2O2 and oxidized NADPH was about 1; superoxide dismutase did not affect the oxidation rate. In scopoletin-mediated oxidation, the stoichiometry was much higher (1:14 in the present experiments); superoxide dismutase considerably increased the oxidation rate. It is concluded that catalysis of NADPH oxidation by the horse radish peroxidase/H2O2 system requires the presence of a mediator molecule. The NADPH oxidation mechanism depends on the intermediary oxidation state of this molecule.
D002384:Catalysis; D006139:Guaiacol / Q000378:metabolism*; D006735:Horseradish Peroxidase / Q000494:pharmacology*; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D007700:Kinetics; D009249:NADP / Q000302:isolation & purification / Q000378:metabolism*; D010084:Oxidation-Reduction; D010544:Peroxidases / Q000494:pharmacology*; D012603:Scopoletin / Q000378:metabolism*; D013482:Superoxide Dismutase / Q000494:pharmacology; D014468:Umbelliferones / Q000378:metabolism*
D014468:Umbelliferones; D009249:NADP; D006139:Guaiacol; D006861:Hydrogen Peroxide; D006735:Horseradish Peroxidase; D010544:Peroxidases; D013482:Superoxide Dismutase; D012603:Scopoletin