Der Einfluß der Temperatur auf die Strahlenempfindlichkeit von Ribonuclease

Abstract

The radiosensitivity of dry ribonuclease was determined at various temperatures ranging from 90 °K to 300 °K and using 60Co gamma-radiation, 2 MeV protons, and 2 MeV deuterons. The cross section for the inactivation of RNase S (T) is, in this range, given as a function of temperature by S(T) =S0+S1·e-Ea/RT. For inactivation of ribonuclease with Co gamma-rays we found S0=0 and Ea=1000 cal/mole; S1= =0.125 Mrad-1 when irradiation is carried out in vacuo, and S1=0.265 Mrad-1 in oxygen. With protons and deuterons the following values were determined: S0=1.28·10-14 cm2, S1=19.5·10-14 cm2, Ea=1050 cal/mole for 2 MeV protons; S0=2.45·10-14 cm2, S1=31·10-14 cm2, and Ea = 1050 cal/mole for 2 MeV deuterons. Furthermore, by analysis of some recent data from the literature we found that the cross section for inactivation by ionizing radiation of various enzymes, bacteriophages, and bacterial spores in the range from 4 °K to temperatures higher than room temperature can satisfactorily be described by the more general equation S(T) =S0+S1·e-E₁/RT+S2·e-E₂/RT, with E1=1 kcal/mole and E2=4 kcal/mole being constant for all objects and for all circumambient conditions tested. This correlation between inactivation cross section S (T) and temperature T shows three mechanisms of inactivation to occur in biological objects: one (S0) being independent of temperature, while the two others have apparent activation energies of 1 kcal/mole and 4 kcal/mole, respectively.