NUCLEOTIDE-ACTIVATED ANION TRANSPORT ACRO SS THE VACUOLAR MEMBRANE FROM PEA LEAVES

Effects of ATP and ADP on the kinetics of artificial and pyrophosphate -dependent Delta pH generation in the tonoplast vesicles from pea (Pis um sativum L.) leaves were studied using acridine orange, a penetratin g Delta pH Indicator. Artificial acidification of the intravesicular w ater phase was created by loading the membrane vesicles with potassium sulphate and then placing them into a slightly alkaline medium withou t potassium ions. pH shift inside the tonoplast vesicles which is indu ced under these conditions by the electrophoretic movement of H+ ions across the membrane and mediated by the electrogenic release or Intrav esicular K+ ions is significantly accelerated in the presence of FCCP, but to a great extent reversed upon ATP or ADP addition to membrane p reparations. Nucleotide-induced Delta pH dissipation was also observed In the absence of ionophores. It does not depend on the presence of M g2+ or sulphate anions in the suspending mixture, but is significantly inhibited by the increase in the osmolarity of the incubation medium br In the concentration of Cl- anions. The ATP/ADP effect was simulate d in the presence of lipophylic penetrating cations, such as tetraphen yl phosphonium. In the tonoplast vesicles which were not loaded with p otassium sulphate, qualitatively similar action of adenine nucleotides was also revealed when the transmembrane pH gradient was generated by tonoplast inorganic pyrophosphatase, although a kinetics of this proc ess was markedly slow. These results indicate that adenine nucleotides allosterically activate the transport system in the tonoplast that ca talyzes the anion efflux From the tonoplast vesicles and, thereby, acc elerates the passive transtonoplast Delta pH dissipation.