Energy-dependent H+ and K+ translocation by the reconstituted yeast plasma membrane ATPase

Abstract

A highly purified plasma membrane ATPase from S. 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. .**GRAPHIC**. but not .**GRAPHIC**. stimulated the rate of ATP hydrolysis in the absence, but not in the presence, of the H+-conducting agent carbonylcyanide m-chlorophenylhydrazone. Na ion on either side of the membrane did not have any stimulatory effect. The K ion translocation driven by ATP hydrolysis appeared to have 2 different kinetic compartments. 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. The yeast plasma membrane ATPase apparently 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 (.DELTA.Gp) to translocate K ion across the cytoplasmic cell membranes.