THE EFFECT OF X-IRRADIATION ON NUCLEASE ACTIVITY AND RESPIRATION OF TETRAHYMENA GELEII W

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Abstract
1. The respiration of X-irradiated Tetrahymena geleii W decreased 30 per cent at 300,000 r and 40 per cent at 500,000 r. The addition of cysteine to the organisms prior to irradiation at 300,000 r afforded approximately 50 per cent protection as measured by oxygen consumption. Homocysteine and pyruvate also gave marked protection while methionine had no effect. Cysteine and glutathione stimulated the respiration of normal cells appreciably, but methionine, serine, glycine and homocysteine had little or no effect. 2. Ribonuclease and desoxyribonuclease activities were not changed significantly in homogenates obtained from whole cells which were irradiated at 300,000 and 500,000 r. However, both enzymes were inhibited by about 50 per cent in homogenates which were irradiated at 500,000 r. For RNase, this inhibition was completely reversed by irradiating in the presence of cysteine. Inhibition of RNase of normal Tetrahymena homogenate by p-chloromercuribenzoate was reversed by cysteine.