84 ELECTROLYTES IN BIOLOGICAL SYSTEMS 



HCOa" and organic anions such as succinate. The binding of cations in undis- 

 sociated complexes must also be considered, particularly in the case of bivalent 

 cations, although a fraction of the K+ may also be bound. Much of the in- 

 organic phosphate that is taken up is converted by the cell into a polymerized 

 form. The function of the transport systems presumably is connected with the 

 accumulation of electrolytes essential for growth and cell division, although in 

 the case of the H+-exchange mechanism, regulation of acid-base balance may 

 also be a factor. 



EFFECT OF IONS ON THE RATE OF METABOLISM 



Lasnitzki (31) found that the rate of fermentation of glucose by yeast cells 

 was considerably enhanced by K+ and Rb+ and to a lesser extent by Cs+ and 

 Na+. Smythe (64) obtained similar results with NH4+. Stimulation of fermenta- 

 tion by K+ was also reported by certain investigators (16, 51), but not by others 

 (3, 32, 4). The lack of uniformity in results in the different experiments may be 

 due to differences in the pn of the medium, which markedly influence the effects 

 of K+. The older reports in the literature suggest that the rate of fermentation 

 is relatively independent of the pH of the medium over a wide range (15, 21, 

 37, 68). However, the earlier studies were usually carried out in the presence of 

 potassium or sometimes phosphate buffers. Thus the individual effects of H+ 

 and K+ were obscured. 



The effect of monovalent cations on rates of metabolism was reinvestigated 

 using buffer systems which themselves had no measureable effect on metabo- 

 lism (48, 49). In the pH range 2.0 to 6.5, triethylamine chloride was used as a 

 cation together with succinic and tartaric acids. In the range 7.5 to lo.o, 

 trishydroxyamino-methane (Tris) proved useful. In the range 6.5 to 7.5, no 

 adequate buffer was found. Triethylamine bicarbonate was used in some ex- 

 periments but manometric measurements are difiicult with high concentrations 

 of bicarbonate. Phosphate was also used, but this ion itself influences metabo- 

 lism. In some experiments in which sugar uptake was measured, the pH was 

 maintained by continuously titrating with triethylamine chloride. 



In the absence of inorganic monovalent cations, the rate of sugar metabolism 

 of yeast cells is markedly influenced by H+. The effect of pn on the rate of 

 fermentation follows a bimodal curve with optima at pn 4.5 and 8.5, a minimal 

 rate at pn 7.0 and a drop-off to low values at pn 2.0 and lo.o (fig. 11). Pre- 

 liminary starvation or treatment with a triethylamine-exchange resin to remove 

 the last traces of ions has only a moderate effect on the rates at the pH optima 

 but markedly depresses the rates at other values of pH (49). 



Potassium stimulates the rate of fermentation only to a smaU extent at the 

 pH optima (pH 4.5 and 8.5) but has a dramatic effect at other values of pH 

 (2.0 to 4.0, and 5.0 to 8.0; table 6). In the presence of high concentrations of 

 K+, the bimodal shape of the pn curve is obliterated and the rate of metabolism 



