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H + /PP i stoichiometry of a membrane‐bound pyrophosphatase of plant mitochondria
Author(s) -
Zancani Marco,
Casolo Valentino,
Vianello Angelo,
Macrí Francesco
Publication year - 1998
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1034/j.1399-3054.1998.1030302.x
Subject(s) - stoichiometry , pyrophosphatase , atpase , membrane , atp hydrolysis , chemistry , substrate (aquarium) , inner mitochondrial membrane , membrane transport , hydrolysis , biophysics , biochemistry , enzyme , biology , organic chemistry , ecology
The H + /PP i stoichiometry of the mitochondrial H + ‐PP i ase from pea ( Pisum sativum L.) stem was determined by two kinetic approaches, and compared with the H + /substrate stoichiometries of the mitochondrial H + ‐ATPase, and the vacuolar H + ‐PP i ase and H + ‐ATPase. Using sub‐mitochondrial particles or preparations enriched in vacuolar membranes, the rates of substrate‐dependent H + ‐transport were evaluated: by a mathematical model, describing the time‐course of H + ‐gradient (ΔpH) formation; or by determining the rate of H + ‐leakage following H + ‐pumping inhibition by EDTA at the steady‐state ΔpH. When the H + ‐transport rates were divided by those of PP i or ATP hydrolysis, measured under identical conditions, apparent stoichiometries of ca 2 were determined for the mitochondrial H + ‐PP i ase and H + ‐ATPase, and for the vacuolar H + ‐ATPase. The stoichiometry of the vacuolar H + ‐PP i ase was found to be ca 1. From these results, it is suggested that the mitochondrial H + ‐PP i ase may, in theory, function as a primary H + ‐pump poised towards synthesis of PP i and, therefore, acting in parallel with the main H + ‐ATPase.