60 



the intracellular concentration of potassium and sodium to 25 percent below that 

 of nonirradiated cells. Potassium was also shown to leak out of irradiated cells 

 that were not treated with Dowex-50, whereas there is no appreciable leakage of 

 potassium from normal yeast cells. 



BENNETT: Were controls run to check the pH under these conditions? 



SHERMAN: Yes. The cells were suspended in triethylamine-succi- 

 nate- tartrate buffer during and after treatment with Dowex-50. The pH of the 

 buffer was adjusted to 4. 5 or 6. 5. 



TOBIAS: Was the fermentative ability of Dowex-50 treated normal 

 cells decreased? 



SHERMAN: Yes. 



TOBIAS: But the irradiated cells decreased more? 



SHERMAN: As much as 90 percent more. 



Bair's experiments (11) suggest that irradiation results in the loss of 

 ability of yeast cells to retain cations. When Dowex-50 is present in the medium 

 after irradiation, the potassium concentration outside the cell is reduced to very 

 low levels. The fact that post-irradiation treatment with Dowex-50 was more 

 effective in revealing damage than treatnnent before irradiation supports this 

 interpretation. The inability of irradiated yeast cells to retain intracellular 

 cations may be the result of interference with the active transport system or 

 conceivably it could result from changes in physical properties of the membrane. 



BARRON: Muntz demonstrated that fermentation will not take place in 

 yeast extracts in the absence of potassium. 



SHERMAN: In E. Coli it has been quite clearly demonstrated that 

 potassium is necessary for growth, synthesis, the incorporation of sulfur into 

 proteins, and the utilization of phosphate (16), so that there seems to be some 

 possibility of relating the radiation effect in potassium -deficient yeast cells to 

 some difficulty in synthesizing protein or at least in getting energy for the syn- 

 thesis of protein. 



COHN: You said that the cells were treated with Dowex-50? 



SHERMAN: Both cells and medium were shaken with the resin. Po- 

 tassium deficiency in E. Coli does not interfere appreciably with glucose uptake. 

 These cells apparently have other pathways for glucose utilization that do not 

 involve potassium. But these pathways result in the production of energy that 

 is not available for synthesis so that the synthetic activity is interfered with. 

 Perhaps this is why these cells are so sensitive to irradiation. It is not that the 

 irradiation has done anything different in potassium -deficient than in normal 

 cells, but in normal cells energy is available for repair. In potassium -deficient 

 cells it is blocked. 



We did some experiments a couple of years ago in which we made yeast 

 cells nitrogen deficient by growing them in low concentrations of ammonium 

 sulfate (8). These cells had a reduced total nitrogen content and also a reduced 

 nucleic acid content. Their anaerobic CO2 production could be inhibited meas- 

 urably with exposures of the order of 5000 r to 10,000 r. There was no appreci- 

 able inhibition of fermentation by these exposures in cells grown in the presence 



