Effect of the Irradiation Temperature on the Production of Free Radicals in Solid Biological Compounds Exposed to Various Ionizing Radiations

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Abstract
Effect of irradiation temperature on the production of secondary radicals in glycine, trypsin, and lysozyme was studied. Solid compounds were irradiated in vacuum, with fast stripped helium, carbon, and argon ions at different temperatures in the range 77[degree] to 320[degree]K. The number of secondary radicals was measured with an ESR-spectrometer after the samples had been kept at room temperature for 20 minutes. The radical yield was independent of irradiation temperature up to 100[degree] to 120[degree]K. At higher temperatures the yield increased, and in the range 77[degree] to 295[degree]K the total variation averaged a factor of 2.2. The yield -versus-temperature curves could be adequately described by a sum of exponential functions. Experiments on trypsin showed a good correlation between production of secondary radicals and loss of enzymatic activity when the irradiation temperature varies. Similarly, a good correlation was found in experiments in which the stopping power of the radiation varied. It is assumed that the loss of enzymatic activity is the result of a sequence of events in which free radicals are important intermediates.

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