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+.

Department of Membrane Transport Czech Academy of Sciences Prague

Extracellular acidification by Saccharomyces cerevisiae in normal and in heavy water

Dependence of the kinetics of secondary active transports in yeast on H(+)-ATPase acidification

Effects of the physiological state of five yeast species on H(+)-ATPase-related processes