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D Ewing

Publications and source records attributed to D Ewing.

51 records · Page 3Linked to original sources
PubMed1980

Breaking survival curves and oxygen removal times in irradiated bacterial spores.

Although there are ambiguities about these results and their interpretations, this unambiguous experimental observation was made: the two kinds of experiments designed to measure deoxygenation times did not give the same answer, for a given N2 flushing rate, unless t-butanol was present. The addition of t-butanol caused large changes in the positions of the survival curve breakpoints, but only small changes in the 'times to anoxia' in the pre-irradiation glushing experiments. Although careful additional work is needed, these initial results suggest that in the spore, the survival curve breakpoint probably does not represent the dose at which anoxia is reached unless t-butanol is present.

Bacillus megaterium↗
PubMed1976

Effects of some -OH scavengers on the radiation sensitization of bacterial spores by p-nitroacetophenone and O2 in suspension.

Spores of Bacillus megaterium were irradiated in suspension with 50 kVp X-rays under three reference conditions: in anoxia (i.e., 100 per cent N2); in anoxia with 2mM p-nitroacetophenone (PNAP), a concentration that shows the maximum amount of sensitization by this agent; and in air. The responses were then measured when different concentrations of an hydroxyl radical scavenger were also present. Allyl alcohol, t-amyl alcohol, t-butanol, ethanol, glycerol, the formate ion, and methanol were the -OH scavengers that were used. A comparison of the effects these additives have on the three reference responses provides indirect, comparative information on the sensitizing processes of PNAP and O2. Neither t-amyl alcohol nor t-butanol affects the response in air or N2 alone. Both these additives, however, can reduce the sensitization from PNAP slightly. The other additives have significant protective effects under the three conditions. In general, the additives have similar effects in air and in 100 per cent N2 but much greater protective effects in PNAP. Although the sensitizing mechanisms are not identified by these experiments, the effects of O2 and PNAP, as judged by the desensitizing actions of these additives, appear quite different.

Acetophenones↗
PubMed1975

Two components in the radiation sensitization of bacterial spores by p-nitroacetophenone: the -OH component.

p-Nitroacetophenone (PNAP) sensitizes Bacillus megaterium spores under anoxic conditions to the lethal effects of 50 kVp X-rays. Concentrations between approximately 5 X 10(-4) M and 3-8 X 10(-3) M produce the maximum effect, an increase of about 30 per cent over the anoxic response when the spores are irradiated in water. Compounds that scavenge -OH decrease, but cannot completely eliminate, this maximum amount of sensitization. These results indicate that PNAP acts to increase spores' radiation sensitivity through two separable types of chemical reactions: one which involves -OH and one which does not. Possible mechanisms responsible for these two components of damage are discussed. In these experiments 1/15 M phosphate buffer acts in several unexpected ways. This concentration itself increased the anoxic spore response by about 9 per cent (relative to the anoxic response in water). In addition, although the maximum amounts of sensitization were the same, the amounts of sensitization from lower PNAP concentrations differed when the suspending fluid was buffer instead of water. An interaction was also seen during the PNAP-t-butanol experiments; again, the responses at low PNAP concentrations were different in buffer and in water. No mechanisms for these actions of this buffer were suggested, although somewhat similar effects may occur with other organisms. Clearly, such effects must be recognized and evaluated before quantitative analyses of the actions of sensitivity-modifying agents can be completed.

Acetophenones↗