Role of alkaline metal ions in the H(+)-ATPase activity of various yeast species.
Saccharomyces cerevisiae, Schizosaccharomyces pombe, Endomyces magnussi, Lodderomyces elongisporus and Rhodotorula gracilis, yeast species ranging from a glycolytic type to a strictly aerobic one, were tested for the activity of their plasma membrane H(+)-ATPase and the effect of alkaline metal cations thereon. The ATP-hydrolyzing activity of membranes from glucose-activated cells ranged from 456 to 932 mumol inorganic phosphate released per min per 1 g membrane protein. The effect of 0.2 M Li+, Na+, K+, Rb+ and Cs+ never exceeded the statistical range of error. In contrast, acidification after glucose addition ranged from 0.15 (for R. gracilis) to 14.8 nmol H+ per min per mg dry weight (for S. cerevisiae) and it was markedly influenced by the presence of alkaline metal chlorides, the highest effect observed being a seven-fold increase by K+ in a S. cerevisiae suspension. The effects were additive to those observed without ions in solution and are ascribed to the operation of independent channels and/or exchange systems for H+ with a clear selectivity toward K+. The separate nature of the ion-triggered extracellular acidification is supported by a different ratio of titration to pH-derived acidity with and without K+.
Kotyk A, Dvoraková M, Georghiou G