Intracellular pH and the kinetics of Rb+ uptake by yeast non-carrier versus mobile carrier-mediated uptake.

The effect of changes in the intracellular pH upon the concentration dependence of the Rb+ uptake by yeast is investigated. It is shown, that the uptake of Rb+ can be described by a mechanism in which the total concentration of primary binding sites at the outer side of the membrane is independent of the intracellular ligand composition and of the membrane potential, and the influx rate constants depend upon the intracellular pH and/or upon the membrane potential. It is argued that the involvement of a mobile carrier mechanism is not likely.