Passive fluxes of K+ and H+ in wild strain and nystatin-resistant mutant of Rhodotorula gracilis (ATCC 26194).

The passive fluxes of protons and potassium ions have been studied in the obligatory aerobic yeast Rhodotorula gracilis. The cellular energy metabolism was suspended by introducing anaerobic conditions. The H+-permeability of the plasma membrane was modified by adding an uncoupler under both aerobic and anaerobic conditions. Unfortunately, the plasma membrane of R. gracilis was insensitive to K+-ionophores. The passive flows of H+ and K+ under anaerobic and/or uncoupled conditions were electrically coupled and exhibited a constant stoicheiometry of 1:1. The H+ permeability of the plasmalemma was shown to determine the velocity of the passive K+-H+ exchange. The nystatin-resistant mutant M 67 displayed distinctly lower permeability for both H+ and K+, which can explain the observed differences in some transport characteristics of the two strains. In order to account for the properties of passive K+ flows, a membrane-potential-gated channel for K+ has been proposed. Evidence is presented that the inhibitor of the plasmalemma-bound H+-ATPase, N,N'-dicyclohexylcarbodiimide (DCCD), reduced at first the permeability for both K+ and H+ and only upon prolonged incubation the ATPase itself. Since DCCD effected an immediate hyperpolarization of the membrane potential, it has been concluded that the H+ does not slip through the H+-ATPase under deenergized conditions.