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.

Catechol oxidation by peroxidase-positive astrocytes in primary culture: an electron spin resonance study

“…Bottom, Computer-simulated spectrum of the 2-hydroxyestradiol o-semiquinone using coupling constants derived from C, top. identical to those observed in Gomori astrocyte granules (Askarov et al, 1984;Van Steveninck et al, 1987). The results of the present study indicate that cysteamine-induced astrocyte peroxidase activity promotes the activation of catechols to semiquinone radicals.…”

Binding of porphyrin to horseradish peroxidase: Effects on structure and function

“…The enhanced activity of HRP with respect to NADH oxidation by HP (Table 3) is in agreement with potentiation effects of HPD and PP on HRP-catalyzed oxidation of NAD(P)H [22,24]. HP and PP also enhance the peroxidase activities of hemoglobin [13,16] and myoglobin [14,16].…”

Haematoporphyrin enhances the peroxidase activity of haemoglobin

“…HP was also found to enhance very efficiently the Hb-catalysed oxidation of NADH (Table 1). Potentiation effects of porphyrins (PP, HP, HpD) on the HRP-catalysed oxidation of NADH or NADPH were reported [27][28][29][30]. However, they had almost no effect on the HRPcatalysed oxidation of o-dianisidine [30] or guaiacol [28].…”

“…Potentiation effects of porphyrins (PP, HP, HpD) on the HRP-catalysed oxidation of NADH or NADPH were reported [27][28][29][30]. However, they had almost no effect on the HRPcatalysed oxidation of o-dianisidine [30] or guaiacol [28]. Takayama and Nakano [31] demonstrated the generation of superoxide anion in the course of NADH or NADPH oxidation in the HRP/H 2 O 2 system.…”

“…This superoxide anion was suggested to inhibit the HRP activity. Van Steveninck et al [28] reported that superoxide radical generation in the HRP/H 2 O 2 / NADPH system was inhibited by the porphyrin, causing potentiation of the enzyme activity. Since superoxide anion generation was not associated with the HRP/H 2 O 2 /o-dianisidine or guaiacol system, HRP activities in these systems were not increased by the porphyrins.…”