Inactivation of catalase and superoxide dismutase by singlet oxygen derived from photoactivated dye

Both superoxide dismutase (SOD) and catalase are: key enzymes in the antiox idant system of the cells that work to maintain low steady-state concentrat ions of the reactive oxygen species. When exposed to a singlet oxygen-produ cing system composed of dye, such as methylene blue or rose bengal, and vis ible light both SOD and catalase were susceptible to oxidative modification and damage as indicated by the loss of activity, fragmentation and aggrega tion of peptide as well as by the formation of carbonyl groups. Histidine, a powerful quenching agent for singlet oxygen, and the polyamines, such as spermine and spermidine, were effective at protecting the activity loss med iated by illuminated dye, whereas spin traps were only mildly effective. Th e structural alterations of modified enzymes were indicated by the increase in susceptibility to proteases, the change in absorption spectra and in fl uorescence spectra. The singlet oxygen-mediated damage to SOD and catalase may result in the perturbation of cellular antioxidant defense mechanisms a nd subsequently lead to a pro-oxidant condition. (C) 2001 Societe francaise de biochimie et biologic moleculaire/Editions scientifiques et medicales E lsevier SAS. All rights reserved.