Evidence for an electrogenic adenosine-triphosphatase in Hevea tonoplast vesicles |
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Authors: | Bernard Marin |
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Institution: | 1. Laboratoire de Physiologie Végétale Appliquée, Université des Sciences et Techniques du Languedoc, Place Eugéne Bataillon, F-34060, Montpellier-Cédex, France
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Abstract: | The function of the Mg-dependent ATPase of Hevea tonoplast in active proton transport was investigated by using a purified tonoplast fraction containing tightly sealed vesicles. In the used experimental conditions, the uptake of 14C]triphenylmethyl-phosphonium ion (14C]TPMP+) and 3H]tetraphenyl-phosphonium ion (3H]TPP+) by the vesicles indicated a transmembrane potential difference, negative inside. In parallel, the uptake of 14C]methylamine into the vesicles monitored a transmembrane pH gradient, interior acid. The addition of 5 mM Mg-ATP markedly depolarized the membrane and increased the magnitude of trnasmembrane pH gradient. These ATP-driven events were substrate specific for Mg-ATP. They were strongly inhibited by ATPase inhibitors such as N, N′-dicyclohexylcar-bodiimide. They were completely eliminated by proton conductors such as carbonylcyanide-p-trifluoromethoxy-phenylhydrazone and 5-chloro-3-tert-butyl-2′-chloro-4-nitro-salicylanilide. They depended on the pH of the medium, the maximum being reached at about pH 7.0. These data provide in vitro evidence that the Mg-ATPase localized at tonoplast level is an electrogenic pump. They are consistent with the hypothesis that an electrogenic H+ pump is catalyzed by the tonoplast ATPase of higher plants. |
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