Über den Einfluß verschiedener Kohlehydratquellen und der osmotischen Verhältnisse auf die Strahlenempfindlichkeit der Zellen von Saccharomyces cerevisiae

Abstract

It was found previously[long dash]that the absence of glucose in the irradiation medium enhances the radio-sensitivity of yeast cells (Saccharomyces cerevisiae) considerably. Consequently, the reason for the radio-protective effect of glucose is now sought. In a first series of experiments, the effect of arabinose and pyruvic acid was compared with that of glucose, with the molarity of all 3 substances kept the same. Preliminary experiments indicated that neither arabinose nor pyruvic acid is metabolized. Nevertheless the pyruvic acid proved to be as effective in radio-protection as glucose, whereas arabinose showed less protective effect. As pyruvic acid has no hydroxyl groups and only little structural similarity to glucose, this result is inconsistent with a direct radio-protective effect of the glucose molecule. In addition, these experiments show that neither the energy production nor any of the connected reactions are responsible for the radio-protective effect of glucose. Thus, the only explanation left is that the changed osmotic pressure influences the radio-sensitivity. For further proof, experiments with different glucose concentrations in the irradiation medium were performed. As expected they showed that the radiation damage was enhanced with decreasing glucose concentration, with the highest sensitivity already reached in a medium of 4% glucose. The possibility that the difference in the osmotic pressure of the preceding culture medium and the irradiation medium enhances the radio-sensitivity was examined. With the concentration of the irradiation medium kept the same, only the glucose concentration of the culture medium was changed. This experiment showed that the radio-sensitivity of yeast cells is not influenced by the difference in the osmotic pressure of the culture medium and the irradiation medium. But on the other hand, it was shown that the osmotic pressure of the culture medium also has an influence on the radio-sensitivity of yeast cells comparable to that of the irradiation medium. In a further experiment, the effects of 2 entirely different culture media, namely, beerwort and a half-synthetic medium were compared, from which it was found that there must be a special radio-protective substance in the beerwort besides the glucose, which extends its effect up to the time of irradiation.