Modifications of gamma-ray sensitivity of bacterial membrane by pre-exposure to light

The exposure of E.coli B/r cells to ultraviolet (UV) or to visible light prior to irradiation with gamma-rays modifies the sensitivity of the cell membrane to the radiation damage responsible for the loss of intracellular K+ content. The experiments reported in the paper have shown: 1. exposure of bacterial cells to sublethal doses of UV light increases their sensitivity to gamma-ray-induced membrane damage, while exposure to visible light has the opposite effect; 2. in combined exposures, the visible light, either given before or after the UV always produces a strong photoprotective effect. In either case, the photosensitizing effect of UV is completely suppressed; 3. the photoprotection decays with time if cell suspensions are left in the dark before gamma-irradiation. At 0 degrees C, the half-life of the photoprotective effect is 25 min at pH 7 and 100 min at pH 7.5. The decay is due to the presence of oxygen; 4. the light band responsible for the induction of photoprotection has been estimated to lie in the wavelength region between 540 and 580 nm.