Differential Modification of Oxic and Anoxic Components of Radiation Damage in Bacillus Megaterium Spores by Caffeine

Summary Studies were carried out on the effect of caffeine on the X-irradiation sensitivity of B. megaterium spores with the following results: Caffeine exerts a concentration-dependent modifying action on oxygen-dependent components of X-ray-induced damage in B. megaterium spore suspensions causing an 'over-O2 effect' at about 1 × 10−4 mol dm−3, and as the concentration is increased to 1 × 10−3 mol dm−3 or above, a small but consistent protection is seen. In the absence of O2, at a wide range of concentrations (8·5 × 10−5 to 1 × 10−1 mol dm−3), caffeine enhances the inactivation constant, k, from 1·17 to about 1·50 kGy−1. Both ethanol and t-butanol (5 × 10−2 mol dm−3) remove the 'over O2-effect' produced by 1 × 10−4 mol dm−3 caffeine in O2; such an effect, however, is not accompanied by reduction in the H2O2 concentrations in the spore suspensions. Ethanol prevents caffeine-induced anoxic sensitization, as well as H2O2 buildup. t-BuOH has no influence on either the low dose part of the log fraction survival curve or on the H2O2 yield in the spore suspensions. Caffeine reacts with radiation-induced e−aq and ·OH with rate constants of 1·5 × 1010 and 6·9 × 109 dm3 mol−1s−1, respectively.