ATP dependence of anion uptake by isolated vacuoles: requirement for excess Mg2+
1990
Dietz, K.J. | Lang, M. | Schonrock, M. | Zink, C.
Vacuoles were isolated from barley mesophyll protoplasts. [14C]Malate or 36Cl- were taken up from the surrounding medium. Uptake was only slightly increased in the presence of equimolar levels of ATP and Mg2+ (as magnesium gluconate). In the presence of excess Mg2+ in the medium, ATP-stimulated uptake of malate and chloride increased several-fold. Stimulation by excess Mg2+ was not observed for ATP-stimulated amino acid uptake by isolated vacuoles. Stimulation of uptake by excess Mg2+ was observed at all malate concentrations upto 10 mmol.l-1. The content of Mg2+ needed for half-maximum stimulation was about 3.5 mmol.l-1 in the presence of 1 mmol.l-1 ATP. The increase in Mg2+ concentration had no effect on the tonoplast ATPase activity.
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