Leakage of phosphate compounds from ultraviolet-irradiated yeast cells

A study was made of the action of ultraviolet radiations on the leekage of radioactive phosphate, P/sup 32/, from uniformly labeled yeast cells. At low dosages leakage is slow and steady for a 24-hr period; at high dosages leakage is rapid and the maximum amount occurs within 4 hr after irradiation. At high dosages 5O% of labeled phosphate of the cells is found in the medium after 4 hr. The pH of the medium influences leakage caused by ultraviolet light. Minimum leakage occurs in the region of pH 6. Above pH 8.7 and below pH 2.6 leakage occurs to a considerable extent in nonirradiated cells. Sodium azide and 2,4- dinitrophenol cause increased leakage in irradiated cells, but these poisons do not cause leakage from nonirradiated cells. Leakage from irradiated cells metabolizing glucose is five times that from irradiated cells having no exogenous substrate. The temperature coefficient or Q/sub 10/ for leakage caused by irradiation is 1.5 for the interval 20 to 30 deg C. A paper chromatographic analysis was made of the leakage products. Positive identification was made of inorganic orthophosphate, 3-phosphoglyceric acid, and adenylic acid. Unique substances appear to be present among the leakage products that are not present in the cells. Leakage is selective. Certain substances that are present in the cell do not leak out following irradiation. The leakage substances resulting from ultraviolet irradiation differ from those resulting from heating the cells at 55 deg C. Cells rendered nonviable by heating leak a considerable additional amount of phosphate which is chromatographically similar to that from cells irradiated but not heated. The possible causes of leakage of phosphate from irradiated cells are discussed. The process is not a simple one but the evidence points to membrane damage allowing diffusion of cellular constituents to the exterior as well as to interference with energy--coupled processes in the cell. (auth)