CHLORIDE TRANSPORT OF YEAST VACUOLAR MEMBRANE-VESICLES - A STUDY OF INVITRO VACUOLAR ACIDIFICATION

Effects of various solutes on acidification inside the vacuolar membrane vesicles of the yeast Saccharomyces cerevisiae were examined. ATP-dependent acidification was stimulated by the presence of chloride salts. There was essentially no difference in the stimulatory effects of NaCl, KCl, LiCl, and choline chloride. The membrane potential across the vacuolar membrane was reduced by the presence of Cl- salts. Transport of Cl-36(-) is driven by the protonmotive force across the vacuolar membrane. Kinetic analyses have revealed that the stimulatory effect of Cl- on internal acidification depends on two distinct components. One shows linear dependency on chloride concentration and is inhibited by 4,4'-diisothiocyano-2,2'-stilbenedisulphonic acid (DIDS). The other exhibits saturable kinetics with an apparent K(m) for chloride of 15-20 mM. We conclude that the vacuolar membrane of yeast is equipped with Cl-transport systems contributing to the formation of a chemical gradient of protons across the vacuolar membrane by shunting the membrane potential generated by proton translocation.