Energy transduction in tonoplast vesicles from red beet (Beta vulgaris L.) storage tissue: H+/substrate stoichiometries for the H+-ATPase and H+-PPase

Arthur L. Schmidt, Donald P. Briskin

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The H+/substrate stoichiometries of the tonoplast H+-ATPase and H+-PPase were determined by a kinetic approach. Using red beet (Beta vulgaris L.) tonoplast vesicles, rates of substrate-dependent H+ transport were estimated by (I) a mathematical model describing the time course of ΔpH formation, (II) the rate of H+ leakage following H+ pump inhibition at a steady state ΔpH, and (III) the initial rate of alkalinization of the external medium. When compared with rates of substrate hydrolysis measured under identical conditions, all three methods yielded an H+/ATP stoichiometry of 2 while the H+/PPi stoichiometry was determined to be 1 using methods I and II. Experimental limitations did not permit an analysis of the H+/PPi, stoichiometry by method III. From these results and the estimated level of substrate and product typically found in the cytoplasm of plant cells, it is suggested that the H+-ATPase and H+-PPase as primary H+-pumps are poised toward net substrate hydrolysis under in vivo conditions thereby operating in parallel to generate a proton electrochemical gradient across the tonoplast.

Original languageEnglish (US)
Pages (from-to)165-173
Number of pages9
JournalArchives of Biochemistry and Biophysics
Issue number1
StatePublished - Jan 1 1993

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Molecular Biology


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