Ion-dependent generation of the electrochemical proton gradient delta muH+ in reconstituted plasma membrane vesicles from the yeast Metschnikowia reukaufii

Estimation of membrane potential deltapsi in reconstituted plasma membrane vesicles using a numerical model of oxonol VI distribution

A model of membrane potential-dependent distribution of oxonol VI to estimate the electrical potential difference deltapsi across Schizosaccharomyces pombe plasma membrane vesicles (PMV) has been developed. deltapsi was generated by the H+-ATPase reconstituted in the PMV. The model treatment was necessary since the usual calibration of the dye fluorescence changes by diffusion potentials (K+ + valinomycin) failed. The model allows for fitting of fluorescence changes at different vesicle and dye concentrations, yielding deltapsi in ATP-energized PMV of 80 mV. The described model treatment to estimate deltapsi may be applicable for other reconstituted membrane systems.

Ionic channels in the plasma membrane of Schizosaccharomyces pombe: evidence from patch-clamp measurements

Patch-clamp studies of the yeast Schizosaccharomyces pombe reveal that the plasma membrane contains a voltage-gated channel mildly selective for potassium over sodium, lithium, and chloride. The channel exhibits several conductances with a maximum of 153 pS. The channel gates in the region of physiologically relevant voltages, being closed at hyperpolarizing and open at depolarizing voltages. It is not inhibited by tetraethylammonium, quinine, or quinidine applied from the cytoplasmic side of the membrane; similarly, ATP and stretch have no effect. The frequency of its occurrence in patches implies that about 35 channels of this kind are present in the plasma membrane of a single cell.

Characterization of a plasma membrane H(+)-ATPase from the extremely acidophilic alga Dunaliella acidophila

Dunaliella acidophila is an unicellular green alga which grows optimally at pH 0-1 while maintaining neutral internal pH. A plasma membrane preparation of this algae has been purified on sucrose density gradients. The preparation exhibits vanadate-sensitive ATPase activity of 2 mumol Pi/mg protein/min, an activity 15 to 30-fold higher than that in the related neutrophilic species D. salina. The following properties suggest that the ATPase is an electrogenic plasma membrane H+ pump. (i) ATP induces proton uptake and generates a positive-inside membrane potential as demonstrated with optical probes. (ii) ATP hydrolysis and proton uptake are inhibited by vanadate, diethylstilbestrol, dicyclohexylcarbodiimide and erythrosine but not by molybdate, azide or nitrate. (iii) ATP hydrolysis and proton uptake are stimulated by fussicoccin in a pH-dependent manner as found for plants plasma membrane H(+)-ATPase. Unusual properties of this enzyme are: (i) the Km for ATP is around 60 microM, considerably lower than in other plasma membrane H(+)-ATPases, and (ii) the ATPase activity and proton uptake are stimulated three to fourfold by K+ and to a smaller extent by other monovalent cations. These results suggest that D. acidophila possesses a vanadate-sensitive H(+)-ATPase with unusual features enabling it to maintain the large transmembrane pH gradient.