THE EFFECT OF X-RADIATION ON ENZYME SYSTEMS OF TETRAHYMENA PYRIFORMIS

¹ William Goldman Isotope Laboratory, Division of Biological Chemistry, Hahnemann Medical College, Philadelphia, Pa., and the Marine Biological Laboratory, Woods Hole, Mass.

1. The effect of 300,000 to 600,000 r on respiration and oxidative and other enzymes of Tetrahymena pyriformis S has been determined. Both homogenates and whole cells were irradiated. At 600,000 r, respiration was significantly decreased; the activities of the succinic, glutamic, and malic dehydrogenase systems, catalase, and DNase were depressed in homogenates irradiated at this level. Within a short time after irradiation, catalase activity was completely recovered in homogenates allowed to stand at 0°. Irradiated cells showed only minor changes in succinic dehydrogenase activity.

2. Whole cells irradiated with 600,000 r in the presence of 2,6-diaminopurine were considerably protected from the effects of radiation on respiration for a short time after exposure. Cells of the W strain, irradiated with 300,000 r and then placed in the presence of L-phenylalanine, showed a loss of ability to oxidize this compound compared to controls. Under the same conditions acetate stimulated the oxygen consumption of x-irradiated cells to a much greater degree than that of control cells when measured 30 minutes after irradiation. Some effects of sulfhydryl reactants on succinic dehydrogenase and deoxyribonuclease activities of homogenates were studied, and the general implications of the results were discussed.