Temperature Dependence of Ionizing Radiation Effect on Dry Lysozyme and Ribonuclease

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Abstract
Dry films prepared from water solutions of lysozyme and ribonuclease A were irradiated in a vacuum with 3-Mev electrons. Sample temperatures were controlled within 2 to 3 degrees in the range 93[degree] to 455[degree]K. Preparations irradiated at various temperatures were brought to ambient, exposed to air, redissolved in appropriate buffers, and assayed for remaining enzymatic activity. Activities were corrected for recovered soluble protein according to biuret response. The 2 enzymes, similar in molecular weight, show significant differences in temperature dependence of the inactivation, represented as a sum of terms differing in activation energy. Previous suggestion of an activation energy in common at room temperature and above for ultraviolet and ionizing radiations on enzymes is contradicted by the result for ribonuclease, and estimates of a middle-term activation energy less than kT are revised upward.