Temperature Dependence of Radiation Sensitivity in the Dry State

Summary

The effects of ionizing radiation on macromolecules and biological systems in the dry state can be described as a function of temperature by three terms, one being independent of temperature, the other two having apparent activation energies of 1 kcal/mole and 4–6·5 kcal/mole, respectively, which are due to the action of radiation-induced radicals. In earlier work, no temperature-dependent component with an activation energy of 1 kcal/mole was reported for the radiation damage on isolated infectious ØX174-DNA. Therefore, inactivation of infectious ØX174-DNA by atomic hydrogen was determined at various temperatures. Freeze-dried DNA samples were exposed to H atoms liberated from a thin organic foil by 30 keV protons, foil and samples being maintained at the same temperature during the exposure. The influence of temperature on the sensitivity of infectious ØX174-DNA molecules towards the action of hydrogen atoms is represented by the relation S(T) = c ^· exp(− E₁/RT) with E₁=(0.91±0.07) kcal/mole. A corresponding component with E₁=(0.97±0.1) kcal/mole could be derived from our experimental data obtained after ionizing irradiation of highly-purified DNA samples at various temperatures. The results support the interpretation that the temperature-dependent part of the inactivation rate, characterized by an apparent activation energy of about 1 kcal/mole, is the result of the action of radiation-induced hydrogen atoms.