Glucose- and K+-induced acidification in different yeast species

The process of acidification of the external medium after addition of gluco se and subsequently of KCI to a suspension of yeast cells varies substantia lly from species to species. After glucose it is most pronounced in Sacchar omyces cerevisiae and Schizosaccharomyces pombe but is very much lower in L odderomyces elongisporus, Dipodascus magnusii and Rhodotorula gracilis. Bot h the buffering capacity and the varied effects of vanadate, suloctidil and erythrosin B indicate that the acidification is by about one-half due to t he activity of plasma membrane H+-ATPase and by about one-half to the extru sion of acidic metabolites from cells. This is supported by the finding tha t a respiratory quotient greater than one (in various strains of S. cerevis iae and in S. pombe) is indicative of a greater buffering capacity and over all acidification of the medium. Taking into account the virtually negligib le buffering capacity of the medium in the pH range where the effect of Kis observed, the effect of K+ is generally of a similar magnitude as that o f adding glucose. It is clearly dependent on (anaerobic) production of meta bolic energy, quite distinct from the dependence of the H+-ATPase-caused ac idification.