922 ADVENTURES IN RADIOISOTOPE RESEARCK 



shall underestimate the extent of the interchange in the case of a strongly 

 pronounced interchange. In this case, the interchange is in fact markedly 

 larger than indicated by the figures of column 5. 



In experiments II and IV, one of the values found experimentally 

 is larger than the value expected in the case of a total interchange. 

 This result may be due to experimental errors, an alternative explanation 

 being the following. In the earliest phase of the experiment, potassium 

 of very high specific activity penetrates into the yeast where it gets 

 partly incorporated in a comparatively stable compound which does 

 not get renewed during the experiment. 



CONCLUSIONS 



As seen in Table 2, already in the course of 2 hours a proportional 

 partition of ^^K between nutrient solution potassium and yeast potassium 

 is obtained, indicating that a full interchange has taken place between 

 the potassium present in the solution and the potassium present in the 

 yeast cells in experiment II, in which the yeast has shown a very strong 

 fermentation. In experiment III, in which the fermentation was much 

 weaker, the extent of exchange was a very restricted one. In experiment I, 

 in which only a slight fermentation took place, about half of the yeast 

 potassium interchanged with solution potassium. In experiments taking 

 22 and 23 hours, respectively, (IV and V), most potassium exchanged. 



In all these experiments, the partition of ^^K added to the nutrient 

 solution between yeast and solution was followed. In another set of 

 experiments, the opposite process. We have grown yeast in a solution 

 containing *^K and suspended the yeast in a nutrient solution containing 

 inactive potassium. In the course of 2 hours, only, a slight interchange 

 took place (II and III); in the course of 20 hours (I), a very appreciable 

 interchange was observed; after the lapse of 44 hours (I), the interchange 

 was complete. In the two last mentioned cases the fermentation was 

 very strong; in the two first mentioned cases the fermentation was 

 restricted. 



A survey of the figures obtained suggests that fermentation promotes 

 interchange between cellular potassium and potassium present in the 

 solution. This result can be interpreted by assuming that potassium per- 

 meates the cell wall of the fermenting yeast easier than the cell wall 

 of non-fermenting yeast. An alternative and not less probable explana- 

 tion is the following: We assume that potassium is partly present in 

 the yeast cells in chemical binding and that the organic compounds 

 containing the potassium degenerate and get resynthesized constantly, 

 and it is in the course of the last mentioned process that ^^K has oppor- 

 tunity to be incorporated into the potassium compounds. It is to be 

 expected that, during intense fermentation, the process of renewal of 



