Photosensitized production of superoxide anion by monochromatic (290-450 nm) ultraviolet irradiation of NADH and NADPH coenzymes

The reduced pyridine coenzymes NADPH and NADH produced superoxide anion (O2-) from ground state molecular oxygen when irradiated by ultraviolet (UV) radiation extending from 290 to 405 nm as detected by cytochrome c reduction. Superoxide dismutase (SOD), but not catalase or heat-activated SOD, decreased the amount of cytochrome c reduced, indicating that O2- was responsible for the reduction of cytochrome c. Decreased oxygen tension during irradiation also inhibited production of O2-. Quantum yields for the production of the anion were in the region of 10-7 to 10-9 mol per photon. These data indicate that NADH and NADPH can act as type II photosensitizers of both far- and near-UV radiation, and that the deleterious biological effects of exposure to these radiations such as erythema and dermal carcinogenesis may be mediated at least in part through the generation of O2-. (author)