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

Abstract

In a previous paper we saw that the absence of glucose in the irradiation medium will enhance the radio-sensitivity of yeast cells (Saccharomyces cerevisiae) considerably. Consequently in the present paper we sought the reason for the radio-protective effect of glucose. In a first series of experiments we compared the effect of arabinose and pyruvic acid with the effect of glucose, keeping the molarity on the same level with all three substances. Preliminary experiments indicated that neither arabinose nor pyruvic acid are metabolised. Nevertheless the pyruvic acid proved to be as effective in radio-protections 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 concentration. After having learned about the significance of the osmotic pressure in the irradiation medium, we examined the possibility, that the difference in the osmotic pressure of the preceding culture medium and the irradiation medium enhances the radiosensitivity. Keeping the concentration of the irradiation medium of the same level now, we changed only the glucose concentration of the culture medium. This experiment showed, that the radiosensitivity of the yeast cells is not influenced by the difference in the osmotic pressure of culture medium and 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. On a further experiment we compared the effect of two entirely different culture media, namely beerwort and a halfsynthetic medium, and we 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.