Interaction of phosphate with monovalent cation uptake in yeast |
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Authors: | GM Roomans GWFH Borst-Pauwels |
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Institution: | Department of Chemical Cytology, Faculty of Science, University of Nijmegen, Toernooiveld, Nijmegen, The Netherlands |
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Abstract: | The uptake of monovalent cations by yeast via the monovalent cation uptake mechanism is inhibited by phosphate. The inhibition of Rb+ uptake shows saturation kinetics and the phosphate concentration at which halfmaximal inhibition is observed is equal to the Km of phosphate for the sodiumindependent phosphate uptake mechanism. The kinetic coefficients of Rb+ and Tl+ uptake are affected by phosphate: the maximal rate of uptake is decreased and the apparent affinity constants for the translocation sites are increased.In the case of Na+ uptake, the inhibition by phosphate may be partly or completely compensated by stimulation of Na+ uptake via a sodium-phosphate cotransport mechanism.Phosphate effects a transient stimulation of the efflux of the lipophilic cation dibenzyldimenthylammonium from preloaded yeast cells and a transient inhibition of dibenzyldimethylammonium eptake. Possibly, the inhibition of monovalent cation uptake in yeast can be explained by a transient depolarization of the cell membrane by phosphate. |
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Keywords: | HEPES |
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