Ca~(2+)/H~+ Antiport as a Possible Mechanism of the Ca~(2+)-Translocating ATPase Functioning in Vesicles of Bean Root Nodule's Symbiosome Membrane

摘要

Using vesicles of symbiosome membrane (SM), it was shown that the Ca~(2+)-ATPase can function as an ATP-energized Ca~(2+)/H~+ antiporter. The initial rate of the acidic shift inside the vesicles, as well as the rate of the ITP-dependent alkalization of the medium inside them markedly increased in the presence of valinomycin. This process was rapidly stopped by eosin Y, a known inhibitor of the type IIB Ca~(2+)-ATPase. ITPdependent uptake of Ca~(2+) was blocked after the addition to the reaction mixture of nigericin in the presence of K~+. Under these conditions, the alkaline shift of pH inside the vesicles occurred, leading to the inhibition of operation of the calcium pump in SM. Evaluation of the pH shifts inside the vesicles by using pH-indicator pyranine confirmed the ion-exchange mechanism of the Ca~(2+)-ATPase functioning in the SM.