Univalent cation fluxes in yeast.
Transport of H+, K+, Rb+ and Tl+ ions was studied in a wild-type strain of Saccharomyces cerevisiae and in its mutants defective in the high-affinity K+ transport system TRK1 and in the double mutant with an additional deletion in the TRK2 gene. In the absence of glucose K+, Rb+ and Tl+ elicited a more or less stoichiometric exchange outflow of H+, in the mutants K+ moved out of cells even in the presence of 10 mM KCl or KNO3. In the presence of glucose in the wild type, K+, Rb+ and Tl+ brought about a massive outflow of H+ while being transported inward against high concentration gradients. In the trk1 delta mutant the exchange fluxes were reduced by 65-85%, in the double mutant those of K+, Rb+ and Tl+ practically cease but outflow of H+ caused by Tl+ remained at the level of the trk1 delta mutant. It appears that, in addition to the H+ export by the PMA1-coded plasma membrane H(+)-ATPase, at least three different univalent-cation involving activities are present: the high-affinity transport system for K+ (TRK1), another system (possibly TRK2) with different responses to K+ and Rb+, vs. Tl+, and an active system for K+ export. The first two are apparently active exchange systems for K+, Rb+, and Tl+ against H+. The source of energy for these highly active transports (acting against gradients of 1000:1 and 5000:1, respectively) is unclear.
Lapathitis
G
G
Institute of Physiology, Prague, Czech Republic.
Kotyk
A
A
D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology*; D027682:Cation Transport Proteins; D002414:Cations, Monovalent / Q000378:metabolism*; D004791:Enzyme Inhibitors; D005656:Fungal Proteins / Q000235:genetics / Q000502:physiology; D005947:Glucose / Q000494:pharmacology; D017136:Ion Transport; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology*; D009154:Mutation; D011188:Potassium / Q000378:metabolism; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors; D011522:Protons; D012413:Rubidium / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D013793:Thallium / Q000378:metabolism
D002352:Carrier Proteins; D027682:Cation Transport Proteins; D002414:Cations, Monovalent; D004791:Enzyme Inhibitors; D005656:Fungal Proteins; D008565:Membrane Proteins; D011522:Protons; D029701:Saccharomyces cerevisiae Proteins; C085258:TRK2 protein, S cerevisiae; C068664:TRK1 protein, S cerevisiae; D013793:Thallium; D006180:Proton-Translocating ATPases; D005947:Glucose; D012413:Rubidium; D011188:Potassium