Plant Molecular Biology Center, McGill University, Montreal, Quebec, Canada H3A 1B1.
Plant Physiol. 1986 Mar;80(3):727-31. doi: 10.1104/pp.80.3.727.
Artificial pH gradients across tonoplast vesicles isolated from storage tissue of red beet (Beta vulgaris L.) were used to study the kinetics of a Ca(2+)/H(+) antiport across this membrane. Ca(2+)-dependent H(+) fluxes were measured by the pH-dependent fluorescence quenching of acridine orange. DeltapH-dependent Ca(2+) influx was measured radiometrically. Both H(+) efflux and Ca(2+) influx displayed saturation kinetics and an identical dependence on external calcium with apparent K(m) values of 43.9 and 41.7 micromolar, respectively. Calcium influx was unaffected by an excess of Mg(2+) but was inhibited by La(3+) > Mn(2+) > Cd(2+). The apparent K(m) for external calcium was greatly affected (5-fold) by internal pH in the range of 6.0 to 6.5 and a transmembrane effect of internal proton binding on the affinity for external calcium is suggested.
利用人工 pH 梯度跨液泡膜分离贮藏组织中的红甜菜(Beta vulgaris L.)质体,研究 Ca(2+)/H(+)反向转运的动力学。通过吖啶橙的 pH 依赖性荧光猝灭来测量 Ca(2+)-依赖性 H(+)通量。放射性测量 ΔpH 依赖性 Ca(2+)内流。H(+)外流和 Ca(2+)内流均显示饱和动力学,并且对外钙的依赖性相同,表观 Km 值分别为 43.9 和 41.7 微摩尔。镁离子过量对钙内流没有影响,但镧(3+)>锰(2+)>镉(2+)抑制钙内流。内部 pH 在 6.0 到 6.5 范围内对外部钙的表观 Km 值有很大影响(5 倍),并且内部质子结合对外部钙亲和力的跨膜效应被暗示。