Kinetical parameters of monovalent cation uptake in yeast calculated on accounting for the mutual interaction of cation uptake and membrane potential

Abstract

Kinetical parameters of monovalent cation uptake in yeast are calculated according to a model for mutual interaction of membrane potential and cation uptake. Apparent K m values for monovalent cation uptake obtained from uptake studies are 3–5-times lower than the K m values expected when the membrane potential remains constant at increasing cation concentrations instead of being reduced. The model accounts for varius phenomena as (i) the increase in apparent K m of Rb + uptake accompanying the decrease in maximum rate of uptake found on increasing the cellular K + content, (ii) the decrease in maximum uptake rate and increase in K m in case of simultaneous transport of phosphate and Rb +, (iii) the change in the maximum uptake rate without a change in K m under conditions that the proton pump is effected and (iv) the absence of an increase in K + efflux at high depolarizing external cation concentrations.