title: Does a proton-pumping ATPase exist in the tonoplast?
abstract: In order to account for the accumulation of metabolites in plant vacuoles, the existence of a proton-pumping ATPase has been widely suggested in the literature. The demonstration of such a tonoplast-bound ATPase was merely based on the characterization of a nitrate-sensitive microsomal fraction. In some examples, this ATPase activity has been evidenced on vacuole preparations obtained under conditions which were criticized by Boller. The application of the reverse phase high-performance liquid chromatography method (RP-HPLC) to the simultaneous separation of adenine nucleotides, in the presence of tonoplast vesicles isolated from Catharanthus roseus, showed results not necessarily correlated with the ATPase hypothesis. Moreover, in light of the H+-quenching of quinacrine fluorescence observed during ATP hydrolysis by vacuoles or tonoplast vesicles, the existence of a proton-pumping ATPase may be questioned.
mesh_terms: D015720:5'-Nucleotidase; D000227:Adenine Nucleotides / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D009708:Nucleotidases / Q000378:metabolism; D010944:Plants / Q000201:enzymology*; D006180:Proton-Translocating ATPases / Q000378:metabolism*; D011796:Quinacrine; D014617:Vacuoles / Q000201:enzymology
chemical_list: D000227:Adenine Nucleotides; D009708:Nucleotidases; D015720:5'-Nucleotidase; D006180:Proton-Translocating ATPases; D011796:Quinacrine