Carcinogenesis
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Reduction of Cr(VI) by NADH and NADPH has been shown to yield Cr(V) species, which have been detected by electron paramagnetic resonance (EPR) spectroscopy. The fine structure on the EPR signal of the Cr(V) species is consistent with the presence of two NAD(P)H ligands in a square-pyramidal arrangement with a single oxygen (oxo) group at the apex. Neither this species nor the initial Cr(VI) complex damage DNA components as evidenced by the lack of effect of these compounds on the optical and EPR signals of the Cr(VI) and Cr(V) species respectively. ⋯ The signals from the former species are consistent with radical addition to the base, whereas the sugar-derived species are believed to be formed via hydrogen atom abstraction. In each case, this behaviour is consistent with hydroxyl radicals being the damaging species in systems where Cr(V) is generated in the presence of hydrogen peroxide. These results therefore suggest that it may be the hydroxyl radical that is the ultimate carcinogenic species in cells and systems exposed to Cr(VI).