ASER ROTHSTEIN 



85 



proceeds at the same high rate over the pii range 2.0 to almost 9.0. The most 

 pronounced effects of K+ are seen at those H+ ion concentrations where the 

 rates are lowest. In fact, at pH 2.0 and 7.0, the rate of fermentation may be 

 almost zero unless K+ is present. Other monovalent cations also have a pro- 

 nounced effect on fermentation at certain values of extracellular pii. Rubidium 



Fig. II. The influence of pH on the uptake of glucose and on the jiroduction of alcohol, 

 lycerol, and COj. 



Table 6. Effect of NH4+ and k+ on the rate of fermentation or glucose at 



DIFFERENT PH's 



Rates are expressed as ^il. of C02/mg of yeast (wet weight) per hour. Ion concentrations 

 were .03 m/1. Buffer, triethylamine (TEA) succinate, tartrate. Glucose, o.i m/1. 



is about half as effective as potassium. Sodium, lithium and cesium all show 

 smaller but significant effects (table 7). None of these ions interferes with the 

 stimulating action of potassium. Ammonium ion is different in its action. It 

 stimulates to the same extent as potassium at pH 7.0, but in contrast, has little 

 effect below pH 4.0 (table 6). 



The interaction of potassium and hydrogen ion has been investigated in 

 some detail in the low pii range (48). As the pn is decreased below 4.5, the 

 rate of metabolism decreases, but the addition of potassium in appropriate 



