Indirect Evidence for Superoxide Anion and Singlet Oxygen Generated by NADPH—NADPH-dependent Cytochrome c Reductase and by l-α-hydroxyacid—l-amino Acid Oxidase at High pH

Summary

The generation of singlet oxygen and superoxide anion during a flavoprotein (NADPH cytochrome c reductase, xanthine oxidase, or l-amino acid oxidase)—substrate-O₂ interaction has been proved indirectly by activation of luminol, which could be inhibited by the addition of either superoxide dismutase or Fe³⁺-ADP complex. Catalase was always added to the system to exclude hydrogen peroxide which probably generates in the system and also activates luminol at pH greater than 8.0. The lowest pH at which light was emitted increased progressively in the xanthine oxidase, cytochrome c reductase, and l-amino acid oxidase system.

In terms of the efficiency of an enzyme in producing both singlet oxygen and superoxide anion at pH 10.0, both l-amino acid oxidase and NADPH cytochrome c reductase systems were distinctly less effective than the xanthine oxidase.