Unbeeinflußbarkeit ihrer Wirkung auf Ribonuclease durch Cystamin und tiefe Temperaturen

Abstract

Slow protons having energies below 1.5 keV dissipate their kinetic energy in matter through elastic nuclear collisions. By this process atoms are displaced out from their original positions in macromolecules. This was recently shown to cause biological damage with high efficiency. Experiments are described to test the possibility of modifying the sensitivity of ribonuclease towards elastic collisions by protective agents and by low temperatures. When cystamine is present during irradiation dry ribonuclease is protected against the action of “ionizing” fast protons (2 MeV), the dose reduction factor being 1.8. But no protection is observed when inactivation is achieved by elastic nuclear collisions (proton energy 1 keV and 1.4 keV). Similar results were obtained when the irradiations were carried out at different temperatures. Using 2 MeV protons the radiosensitivity of ribonuclease was found to be 3 times higher at room temperature than at 125 °K, but when using slow protons of 1.4 keV energy the inactivation cross section turned out to be independent of temperature. This shows that the action of elastic nuclear collisions can be modified neither by cystamine nor by low temperatures.