Similarities in the Effects of Oxygen and Nitric Oxide on the Rate of Inactivation of Vegetative Bacteria by X-Rays

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Abstract
The effects of O2 and NO on the sensitivity to 250 kv X-rays of Shigella sonnei were investigated. The experiments were carried out with the bacillus in aqueous suspension and under conditions favorable for the precise control of the amount of dissolved gases present during the irradiation. It was found that, as regards effect on radiosensitivity in this system, NO was equivalent to O2, molecule for molecule. The solubility of NO is about 50% greater than that of O2, so that a lower partial pressure in the gas phase was needed. It was found that 1.6 [mu][image] of either gas sufficed to double the radiosensitivity and that the concentration of O2 required did not depend upon temperature between 2[degree] and 30[degree] C. The effect of 100 [mu][image] NO was to raise the radiosensitivity of anoxic bacteria by a factor of 2.7. The increase in radiosensitivity caused by O2 was about the same. NO also increased the radiosensitivity of haploid yeast and was not toxic to either organism at temperatures below 15[degree] C. These data are more readily explained on the hypothesis that both gases increase the radiation injury by virtue of their affinity for radiation-induced C radicals in the cell constituents, rather than through any metabolic action, as NO has an affinity for Fe-containing enzymes and is known to inhibit certain metabolic processes.

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