Titratable acidity of the extracellular medium was compared with that calculated from pH changes in a suspension of Saccharomyces cerevisiae. After addition of cells to normal water the ratio of titratable acidity to the computed one was about 25, after addition of 50 mmol/L D-glucose it was about 13, after subsequent addition of K+ ions it was only 2. In heavy water the respective values were 30, 9, and 1. Apparently, the principal buffer-generating processes have to do with glucose metabolism but little with the K+/H+ exchange observed after addition of K+. D2O appears to block processes producing the buffering capacity of the medium, among them possibly extrusion of organic acids.

• MeSH
• Potassium Chloride pharmacology   MeSH
• Hydrogen-Ion Concentration MeSH
• Acids metabolism   MeSH
• Deuterium Oxide pharmacology   MeSH
• Buffers MeSH
• Saccharomyces cerevisiae drug effects   metabolism   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Comparative Study MeSH
• Names of Substances
• Potassium Chloride MeSH
• Acids MeSH
• Deuterium Oxide MeSH
• Buffers MeSH

Acidification of the external medium of the yeast Saccharomyces cerevisiae, mainly caused by proton extrusion by plasma membrane H(+)-ATPase, was inhibited to different degrees by D2O, diethylstilbestrol, suloctidil, vanadate, erythrosin B, cupric sulfate and dicyclohexylcarbodiimide. The same pattern of inhibition was found with the uptake of amino acids, adenine, uracil, and phosphate and sulfate anions. An increase of the acidification rate by dioctanoylglycerol also increased the rates of uptake of adenine and of glutamic acid. In contrast, a decrease of the membrane potential at pH 4.5 from a mean of -40 to -20 mV caused by 20 mM KCl had no effect on the transport rates. The ATPase-deficient mutant S. cerevisiae pmal-105 showed a markedly lower uptake of all the above solutes as compared with the wild type, while its membrane potential and delta pH were unchanged. Other types of acidification (spontaneous upon suspension; K+ stimulated) did not affect the secondary uptake systems. A partially competitive inhibition between some individual transport systems was observed, most pronouncedly with adenine as the most avidly transported solute. These observations, together with the earlier results that inhibition of H(+)-ATPase activity affects more the acidic than the basic amino acids and that it is more pronounced at higher pH values and at greater solute concentrations, support the view that it is the protons in or at the membrane, as they are extruded by the ATPase, that govern the rates of uptake by secondary active transport systems in yeast.

• MeSH
• Biological Transport, Active MeSH
• Kinetics MeSH
• Hydrogen-Ion Concentration MeSH
• Membrane Potentials MeSH
• Proton-Translocating ATPases antagonists & inhibitors   metabolism   MeSH
• Saccharomyces cerevisiae enzymology   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Proton-Translocating ATPases MeSH

Effects of starvation and glucose preincubation on membrane potential, ATPase-mediated acidification and glutamic acid transport were studied in yeast species Saccharomyces cerevisiae, Schizosaccharomyces pombe, Dipodascus magnusii, Lodderomyces elongisporus and Rhodotorula gracilis. The membrane potential was highest after preincubation with glucose in all species but L. elongisporus and R. gracilis. In all cases the membranes were depolarized in the presence of 20 mmol/L KCl and hyperpolarized with 50 mumol/L diethylstilbestrol (DES). The extracellular acidification caused by addition of glucose was highest after preincubation with glucose in all cases except in R. gracilis where there was none. In all cases except in R. gracilis addition of KCl caused a marked increase in the acidification rate. Addition of DES with glucose caused a large decrease in rate in S. cerevisiae but had much less effect on the other species. Transport of glutamic acid was clearly increased after pretreatment with glucose in S. cerevisiae, S. pombe and D. magnusii (mainly due to enhanced synthesis of the carrier) but actually decreased in R. gracilis and L. elongisporus. Addition of DES had an inhibitory effect in all species but much more pronounced in S. cerevisiae and S. pombe than in others. In general, both the acidification and the transport of glutamate were enhanced after preincubation with glucose but much more so in the semianaerobic species, such as S. cerevisiae, than in the strict aerobes (R. gracilis) where the effect was occasionally negative. There was no relationship between the ATPase-mediated acidification and the membrane potential.

• MeSH
• Biological Transport, Active MeSH
• Diethylstilbestrol pharmacology   MeSH
• Species Specificity MeSH
• Glucose pharmacology   MeSH
• Glutamates pharmacokinetics   MeSH
• Kinetics MeSH
• Hydrogen-Ion Concentration MeSH
• Yeasts drug effects   metabolism   MeSH
• Glutamic Acid MeSH
• Membrane Potentials drug effects   MeSH
• Proton-Translocating ATPases metabolism   MeSH
• Rhodotorula drug effects   metabolism   MeSH
• Saccharomyces cerevisiae drug effects   metabolism   MeSH
• Saccharomycetales drug effects   metabolism   MeSH
• Schizosaccharomyces drug effects   metabolism   MeSH
• Publication type
• Journal Article MeSH
• Comparative Study MeSH
• Names of Substances
• Diethylstilbestrol MeSH
• Glucose MeSH
• Glutamates MeSH
• Glutamic Acid MeSH
• Proton-Translocating ATPases MeSH