Rasi-Caldogno F, Pugliarello M C, De Michelis M I
Centro di Studio del Consiglio Nazionale delle Ricerche per la Biologia Cellulare e Molecolare delle Piante, Università di Milano, Via G. Celoria 26, 20133 Milano, Italy.
Plant Physiol. 1987 Apr;83(4):994-1000. doi: 10.1104/pp.83.4.994.
Microsomal vesicles from 24-hour-old radish (Raphanus sativus L.) seedlings accumulate Ca(2+) upon addition of MgATP. MgATP-dependent Ca(2+) uptake co-migrates with the plasma membrane H(+)-ATPase on a sucrose gradient. Ca(2+) uptake is insensitive to oligomycin, inhibited by vanadate (IC(50) 40 micromolar) and erythrosin B (IC(50) 0.2 micromolar) and displays a pH optimum between pH 6.6 and 6.9. MgATP-dependent Ca(2+) uptake is insensitive to protonophores. These results indicate that Ca(2+) transport in these microsomal vesicles is catalyzed by a Mg(2+)-dependent ATPase localized on the plasma membrane. Ca(2+) strongly reduces DeltapH generation by the plasma membrane H(+)-ATPase and increases MgATP-dependent membrane potential difference (Deltapsi) generation. These effects of Ca(2+) on DeltapH and Deltapsi generation are drastically reduced by micromolar erythrosin B, indicating that they are primarily a consequence of Ca(2+) uptake into plasma membrane vesicles. The Ca(2+)-induced increase of Deltapsi is collapsed by permeant anions, which do not affect Ca(2+)-induced decrease of DeltapH generation by the plasma membrane H(+)-ATPase. The rate of decay of MgATP-dependent DeltapH, upon inhibition of the plasma membrane H(+)-ATPase, is accelerated by MgATP-dependent Ca(2+) uptake, indicating that the decrease of DeltapH generation induced by Ca(2+) reflects the efflux of H(+) coupled to Ca(2+) uptake into plasma membrane vesicles. It is therefore proposed that Ca(2+) transport at the plasma membrane is mediated by a Mg(2+)-dependent ATPase which catalyzes a nH(+)/Ca(2+) exchange.
来自24小时龄萝卜（Raphanus sativus L.）幼苗的微粒体囊泡在添加MgATP后会积累Ca(2+)。MgATP依赖性Ca(2+)摄取在蔗糖梯度上与质膜H(+)-ATPase共同迁移。Ca(2+)摄取对寡霉素不敏感，受钒酸盐（IC(50) 40微摩尔）和赤藓红B（IC(50) 0.2微摩尔）抑制，且在pH 6.6至6.9之间显示出最佳pH值。MgATP依赖性Ca(2+)摄取对质子载体不敏感。这些结果表明，这些微粒体囊泡中的Ca(2+)运输是由位于质膜上的Mg(2+)-依赖性ATPase催化的。Ca(2+)强烈降低质膜H(+)-ATPase产生的ΔpH，并增加MgATP依赖性膜电位差（Δψ）的产生。Ca(2+)对ΔpH和Δψ产生的这些影响在微摩尔浓度的赤藓红B作用下大幅降低，表明它们主要是Ca(2+)摄取到质膜囊泡中的结果。Ca(2+)诱导的Δψ增加被渗透性阴离子消除，而渗透性阴离子不影响Ca(2+)诱导的质膜H(+)-ATPase产生的ΔpH降低。在抑制质膜H(+)-ATPase后，MgATP依赖性ΔpH的衰减速率因MgATP依赖性Ca(2+)摄取而加快，表明Ca(2+)诱导的ΔpH降低反映了与Ca(2+)摄取到质膜囊泡中相关的H(+)外流。因此，有人提出质膜上的Ca(2+)运输是由Mg(2+)-依赖性ATPase介导的，该酶催化nH(+)/Ca(2+)交换。
