Characterization of a proton pump from pea stem microsomes |
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Authors: | A. VIANELLO,F. MACRÍ |
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Affiliation: | CNR Institute of Plant Biosynthesis, Section of Padova, Corso Stati Uniti 4, I-35100 Padova, Italy, and Institute of Plant Protection, University of Udine, P. le M. Kolbe 4, 1-33100 Udine, Italy |
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Abstract: | Abstract The present work deals with the characterization of an ATP-dependent proton translocation monitored by the ΔpH probe acridine orange. The ATP-dependent proton translocation has an optimum activity at pH 6.5 and is substrate specific for ATP. It is stimulated by Cl−, HCO3− and Br−, but is insensitive to several monovalent cations. Divalent cations (Mg2+ or Mn2+) are required for proton translocation, while in the presence of Ca2+ no uptake is observed. NO3−, NO2− and citrate strongly inhibit proton uptake. On the contrary, F−, SO42−, malate, pyruvate, succinate, oxalate and acetate have no inhibitory effect. Proton uptake is stimulated by valinomycin and unaffected by molybdate. Two thiols, dithioerythritol and dithiothreitol, are able partially to prevent the FCCP-abolished proton uptake or partially restore the ATP-dependent proton translocation in FCCP-collapsed vesicles. It is suggested that pea stem microsomes possess an electrogenic ATPase, acting as a proton pump, which, on the basis of its characteristics, can be tentatively associated with membranes of tonoplast origin. |
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Keywords: | Pisum sativum L. Leguminosae pea microsomal vesicles proton translocation acridine orange |
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