The effects of ionizing radiation on trypsin. I. Losses of esterase and protease activities of trypsin and trypsin-inhibitor compound

Abstract Crystalline trypsin and trypsin-inhibitor (T-I) compound were irradiated as dry solids in vacuo with cesium-137 γ-rays up to 50 megarads. Results followed first-order inactivation curves, consistent with a target theory. For trypsin esterase and protease activities, D 37 values were 33 and 26.8 megarads, respectively, and for T-I compound 22 and 14 megarads, respectively. Postirradiation exposure to oxygen enhanced the loss of both activities, with the esterase activity lost at a greater rate and becoming equal to the rate of loss of protease activity. These results were discussed in terms of possible structural changes in the trypsin caused by radiation.