Effects of Oxygen on the Inactivation of Enzymes by Ionizing Radiations: II. Solid Trypsin and Deoxyribonuclease

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Abstract
The inactivation of solid trypsin by ionizing radiation was studied in the presence and in the absence of oxygen. With 15-Mev electrons pulses (2.5 X107 rads/sec in the pulse no oxygen effect is observed, but oxygen increases inactivation at low dose rates. With deoxyribonuclease an oxygen effect was observed even with the pulsed electrons. The lack of an oxygen effect with trypsin at high dose rates is attributed to the slowness of oxygen reactions. When cysteine is present, oxygen has a marked effect even at the high dose rates. The inactivation dose of the solid depends markedly on its method of preparation. In the most sensitive state at least 4 molecules of the enzyme are inactivated by one ionization Some theoretical considerations are given, based on the concept that additives, such as cysteine, may facilitate the neutralization of the charge molecules formed by the initial ionizations.