title: The mechanism of potentiation of horseradish peroxidase-catalysed oxidation of NADPH by porphyrins.
abstract: Several porphyrins, including HpD (haematoporphyrin derivative), potentiate the oxidation of NADPH by horseradish peroxidase/H2O2. To elucidate the mechanism of potentiation, the following observations are relevant. During peroxidase-catalysed NADPH oxidation, O2-.(superoxide radical) is generated, as judged from superoxide dismutase-inhibitable cytochrome c reduction. This generation of O2-. is suppressed by HpD. Peroxidase-catalysed NADPH oxidation is stimulated by superoxide dismutase and by anaerobic conditions. Under anaerobic conditions HpD has no influence on peroxide-catalysed NADPH oxidation. Previous studies have shown that horseradish peroxidase is inhibited by O2-.. Thus the experimental results indicate that the potentiating effect of HpD can be explained by its ability to inhibit O2-. generation in the horseradish peroxidase/H2O2/NADPH system.
mesh_terms: D002384:Catalysis; D003574:Cytochrome c Group / Q000378:metabolism; D004357:Drug Synergism; D006139:Guaiacol / Q000378:metabolism; D017324:Hematoporphyrin Derivative; D006415:Hematoporphyrins / Q000494:pharmacology*; D006735:Horseradish Peroxidase / Q000494:pharmacology*; D009249:NADP / Q000378:metabolism*; D010084:Oxidation-Reduction; D010544:Peroxidases / Q000494:pharmacology*; D013481:Superoxides / Q000378:metabolism
chemical_list: D003574:Cytochrome c Group; D006415:Hematoporphyrins; D013481:Superoxides; D009249:NADP; D017324:Hematoporphyrin Derivative; D006139:Guaiacol; D006735:Horseradish Peroxidase; D010544:Peroxidases