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ATP‐dependent H + ‐pumping of a low‐density fraction of pea stem microsomes
Author(s) -
Vianello Angelo,
Macrì Francesco,
Antone Paolo Dell'
Publication year - 1987
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 - 10.1111/j.1399-3054.1987.tb04614.x
Subject(s) - oligomycin , vanadate , electrochemical gradient , chemistry , atpase , proton transport , ouabain , proton , membrane potential , biophysics , biochemistry , enzyme , membrane , biology , sodium , physics , organic chemistry , quantum mechanics
A low‐density fraction of pea ( Pisum sativum L. cv. Alaska) stem microsomes, obtained from a discontinuous sucrose gradient, possessed an H + ‐ATPase able to generate a proton gradient and an electrical potential. The proton pumping was insensitive to monovalent cations, to vanadate and oligomycin, required a permeant anion and was inhibited by nitrate, N, N'‐dicyclohexylcarbodiimide and diethylstilbestrol. The H + ‐ATPase had a pH optimum around 6.0–6.5 and was saturable with respect to the substrate Tris‐ATP (K m ≅ 0.4 m M ). Ca 2+ (0.05–1 m M ) induced a dissipation of the ATP‐generated δpH without affecting ATPase activity. At physiological concentrations (1–5 m M ), nitrate caused an initial slight increase of the ATP‐generated proton gradient followed by a complete dissipation after 2–3 min. The dissipating effect was not caused by inhibition of ATPase activity, since ATP prevented the nitrate‐induced collapse of δpH. On the other hand, ATPase activity, evaluated as release of P i , was not inhibited by concentrations lower than 20 m M KNO 3 . These results indicate that nitrate entered the vesicles in response to an electrical potential and then could exit in symport with protons, while Ca 2+ entered in exchange for protons (antiport).