The oxygen effect: variation of the K-value and lifetimes of O2-dependent damage in some glutathione-deficient mutants of Escherichia coli.
Radiosensitization by various concentrations of O2 has been studied in an Escherichia coli K-12 wild-type strain and some derived glutathione (GSH)-deficient mutants using 60Co gamma-irradiation. The maximum oxygen enhancement ratio (OER) and the K-value, the O2 concentration that produced half the maximum O2 effect, were found to depend on the GSH biosynthetic capacity of the strains. For the GSH+ wild-type strain, AB1157, and the GSH- mutant, 830, which is deficient in glutathione synthetase, the final enzyme in the GSH biosynthetic pathway, the maximum OERs were both about 3.9 and the K-values were 0.53% and 0.24% O2, respectively. On the other hand, the maximum OERs for two GSH- mutants, 7 and 821, both deficient in gamma-glutamylcysteine synthetase, the penultimate enzyme in the GSH biosynthetic pathway, were about 2.7 and the K-values were about 0.06% O2 for both. The fast chemical repair of O2-dependent damage in these strains was measured using a fast mixing and irradiation method, the gas explosion technique. The chemical repair rates in the various E. coli strains varied approximately in proportion to the O2 K-values, and both the rates of chemical repair and the K-values correlated approximately with the levels of non-protein sulphydryls in the various strains.
Harrop
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Cancer Research Campaign Gray Laboratory, Mount Vernon Hospital, Northwood, Middlesex, UK.
Held
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Michael
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D003037:Cobalt Radioisotopes; D004249:DNA Damage; D004926:Escherichia coli / Q000187:drug effects / Q000528:radiation effects*; D005720:Gamma Rays; D005978:Glutathione / Q000502:physiology*; D009154:Mutation; D010100:Oxygen / Q000502:physiology*; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*
D003037:Cobalt Radioisotopes; D011838:Radiation-Sensitizing Agents; D005978:Glutathione; D010100:Oxygen