Bacteria form intracellular free radicals in response to paraquat and streptonigrin. Demonstration of the potency of hydroxyl radical

D. J. Hassett, B. E. Britigan, T. Svendsen, G. M. Rosen, M. S. Cohen

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Abstract

The generation of oxygen reduction products by Neisseria gonorrhoeae FA1090 upon exposure to streptonigrin (SNG) and paraquat (PQ2+) and their toxicity was examined. N. gonorrhoeae exhibited maximal cyanide-insensitive respiration, which was employed as an indicator of superoxide (O2-) formation, in the presence of 0.064 mM streptonigrin and 90 mM PQ2+, respectively. Using the concentration of SNG and PQ2+ described above, complete lethality (>108 cells/ml) was observed among cells exposed to SNG, whereas PQ2+ reduced viability by only 3 logs. In an attempt to determine the oxygen radical species generated by gonococci when exposed to SNG, dimethyl sulfoxide, Fe3+, KCN, and the spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), we were able to detect .OH manifested as the methyl adduct (DMPO-CH3). The production of the latter species was not inhibited by catalase, suggesting intracellular .OH generation. When PQ2+ was substituted for SNG, only low levels of DMPO-CH3 were observed, the production of which ceased within 8 min. SNG and PQ2+, added to a O2--generating system in the presence of Fe3+, promoted increased .OH generation. The iron chelator diethylenetriaminepentaacetic acid enhanced the generation of spin-trapped .OH and O2- in the presence of PQ2+. The addition of catalase to this system, however, eliminated the DMPO-CH3 signal, showing that the .OH in this system was extracellular. PQ2+-mediated generation of extracellular .OH in the presence of Fe3+-diethylenetriaminepentaacetic acid EDTA did not enhance the killing of gonococci by PQ2+. These data show that the lethality of SNG relative to PQ2+ is due to the inherent ability of SNG to catalyze the formation of critical levels of intracellular .OH, detectable through the use of spin trapping techniques.

Original languageEnglish (US)
Pages (from-to)13404-13408
Number of pages5
JournalJournal of Biological Chemistry
Volume262
Issue number28
Publication statusPublished - Nov 27 1987

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ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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