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  • Title: Mechanistic aspects of paraquat toxicity in E. coli. A spin trapping study.
    Author: Sion A, Samuni A, Chevion M.
    Journal: Biochem Pharmacol; 1989 Nov 15; 38(22):3903-7. PubMed ID: 2557034.
    Abstract:
    Mechanistic aspects of paraquat monocation radical (PQ.+) and copper involvement in paraquat toxicity have been examined using E. coli B cells. Electron spin resonance (ESR) spectrometry combined with cell survival studies were used to explore the correlation between radical production and biological damage. The line broadening agent oxalato-chromiate (CrOx) was used to characterize the anoxic partition of PQ.+ inside and outside the cell. In the presence of CrOx the ESR signal was totally eliminated, indicating that intracellular species were undetectable and that, contrary to previous reports, PQ.+ exclusively accumulates outside the cell. The PQ.+ radical does not react with H2O2 but disappears in the presence of H2O2 when catalytic traces of Cu(II) are present. Spin-trapping studies using DMPO showed that in aerobic environment paraquat-induced O2 radicals are detectable exclusively in the extracellular compartment. The correlation between PQ.+ appearance and the biological damage is not simple. PQ.+ non-toxically accumulates, in the absence of oxygen and either Cu(II) or H2O2. By contrast, with both H2O2 and Cu(II) the cells are rapidly killed but PQ.+ was undetectable. These results reconfirm the key catalytic mediatory function of transition metals in paraquat toxicity.
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