THE ROLE OF SUPEROXIDE RADICAL IN CHROMIUM(VI)-GENERATED HYDROXYL RADICAL - THE CR(VI) HABER-WEISS CYCLE

To understand the role of the superoxide (O2-) radical in chromate-related genotoxicity, we investigated whether Cr(VI) can catalyze the Haber-Weiss cycle in vitro: O2- + Cr(VI) → Cr(V) + O2 Cr(V) + H2O2 → Cr(VI) + ·OH + OH-. ESR and spin trapping techniques were utilized to monitor the O2- (produced using xanthine/xanthine oxidase), ·OH, and Cr(V) species. Superoxide dismutase as well as catalase inhibited the ·OH radical radical formation, attesting to the direct involvement of O2- and H2O2 in the process. ESR measurements also provided direct evidence for the formation of Cr(V). Kinetic measurements were consistent with the role of Cr(V) and H2O2 as intermediates in ·OH formation. These results indicate that in cellular media, especially during chromate phagocytosis, the O2/t radical can become a significant source of ·OH radicals and hence a significant factor in the biochemical mechanism of cellular damage due to Cr(VI) exposure. © 1992.