PubMed · 7416072
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A S Feigenbaum, J K Luce. 1980. Potassium supplementation.. https://doi.org/10.1093/ajcn%2F33.9.2053
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Phorbol ester treatment of granulocytes triggers release of superoxide (O2.-) and a concomitant burst of DNA strand breaks. The relationship between the amount of O2.- and the number of DNA breaks has not previously been explored. To quantify the relatively large amount of O2.- generated over a 40-min period by 1 x 10(6) granulocytes/mL, a discontinuous "10-min pulse" method employing cytochrome c was used; 140 nmol O2.- per 1 x 10(6) cells was detected. DNA strand breaks were quantified by fluorimetric analysis of DNA unwinding (FADU). To vary the level of O2.- released by cells, inhibitors of the respiratory burst were used. Sodium fluoride (1-10 mM) and staurosporine (2-10 nM) both inhibited O2.- production. In both cases, however, inhibition of strand breakage was considerably more pronounced than inhibition of O2.-. Zinc chloride (50-200 microM) inhibited both O2.- and DNA breaks, approximately equally. Dinophysistoxin-1 (okadaic acid) inhibited O2.- production more effectively than it inhibited DNA breaks. O2.- dismutes to H2O2, a reactive oxygen species known to cause DNA breaks. The addition of catalase to remove extracellular H2O2 had no effect on DNA breakage. Using pulse field gel electrophoresis, few double-stranded breaks were detected compared to the number detected by FADU, indicating that about 95% of breaks were single-stranded. The level of DNA breaks is not directly related to the amount of extracellular O2.- or H2O2 in PMA-stimulated granulocytes. We conclude that either an intracellular pool of these reactive oxygen species is involved in breakage or that the metabolic inhibitors are affecting a novel strand break pathway.
This paper presents a rigorous derivation of a theory for the calculation of the frequency-dependent dielectric properties of each component of the system protein/water/ions with the aim of enabling comparison to experimentally determined dielectric properties. We apply this theory to a very long (13.1 ns) molecular dynamics simulation of an HIV1 zinc finger peptide, its co-ordinated zinc ion, and two chloride ions in a box of SPC/E water molecules. We find the dielectric relaxation of the water molecules restricted compared to pure water, giving rise to a static dielectric constant for the water-component of only 47. The peptide is found to have a complicated dielectric relaxation behaviour, with a static dielectric constant of 15. We also calculate the frequency-dependent conductivity of the ions in this system. We analyze all contributions to the calculation of these dielectric properties and find that the coupling between the dielectric relaxation of the peptide and that of the water-component is particularly important for correctly describing the dielectric constant of the peptide.
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