A highly purified plasma membrane ATPase from the yeast Schizosaccharomyces pombe incorporated into liposomes was able to carry out translocation of H+ and K+ in the absence of the substrate ATP, when a membrane potential of appropriate polarity was applied. In the absence of ATP, the membrane potential induced K+ translocation was strongly inhibited by the ATPase inhibitor vanadate. [Formula: see text], but not [Formula: see text], stimulated the rate of ATP hydrolysis in the absence, but not in the presence, of the H+-conducting agent carbonylcyanide m-chlorophenylhydrazone. Sodium ion on either side of the membrane did not have any stimulatory effect. The potassium ion translocation driven by ATP hydrolysis appeared to have two different kinetic components. Although the ATP-dependent K+ transport strictly required the presence of a membrane potential, the rate of K+ translocation was not affected by a broad modulation of the degree of coupling (q) between ATP hydrolysis and the electrogenic H+ translocation. These experiments support the view that the yeast plasma membrane ATPase not only uses the membrane potential generated by the electrogenic H+ translocation, but also uses part of the free energy of the hydrolysis of ATP (ΔGP) to translocate potassium ion across the cytoplasmic cell membrane.
A temperature-sensitive mutant of the yeast plasma membrane ATPase obtained by in vitro mutagenesis
