On the Mechanism of Oxygen Protection against Ionizing Radiation Damage in the Cell Wall of Micrococcus radiodurans

resulting in an increase in the ratio of oxic to anoxic damage with increasing concentration of these compounds, until 02 (and nitroaromatic compounds) become relative radiosensitizers. More than one free-radical intermediate species appears involved, and for every final sensitive site which causes the release of a wall component, there are many potential intermediate radicals. It is postulated that oxygen protection results from a reaction of 02 with an intermediate wall radical. Possible mechanisms for other competing reactions are discussed.