66 



ELECTROLYTES IN BIOLOGICAL SYSTEMS 



on the rates of metabolism are due to the action of those electrolytes on the 

 enzymes of the cell surface. 



It should be emphasized that the material presented here is specifically con- 

 cerned with the properties of yeast cells, and that the patterns of electrolyte 

 metabolism may be considerably different in other cells. 



ELECTROLYTE CONTENT OF YEAST 



The electrolyte content of baker's yeast as it is grown commercially (Stand- 

 ard Brands) is given in table i. The predominant cation is potassium and the 

 anions, bicarbonate and phosphate. If the electrolytes are homogeneously 

 distributed in the cell, then the electrolyte concentration in the cytoplasm is 

 about 0.2 molar. The electrolyte composition is not constant but can be al- 

 tered over a wide range. Thus the ionic composition of the growth medium plays 

 an important role in determining the final ionic content of the cells. Even in a 



non-growing population, the electrolyte content can be markedly altered. 

 For example, if yeast is starved, it will slowly lose potassium (51, 63), falling 

 from a normal level of about 0.15 m/1. to about 0.06 m/1. after 24 hours. The 

 loss of potassium can be accelerated by shaking with cation exchange resins. 

 On the other hand, the potassium content can be increased to about 0.25 

 M/1. by adding glucose to cells in the presence of relatively high concentrations 

 of potassium (51). The potassium can be replaced by sodium, to some extent, 

 if glucose is added in the presence of high concentrations of sodium (5), or in 

 the presence of high concentrations of NaF (63). Yeast populations have been 

 prepared in which the K+ has been completely replaced by Na+ or by NH4"^ 

 (7, 11). The phosphate content can also be increased if cells are suspended in 

 glucose plus orthophosphate, especially if K+ or Mg++ are also present (62). 

 Most of the additional phosphate appears in the cell as an inorganic metaphos- 

 phate (28, 62, 70). The bivalent ion content can also be increased up to 100% 

 if the yeast is suspended in glucose, bivalent cation and potassium phosphate 

 (62, 53). 



