A comparative study on sugar beet root (Na⁺+K⁺)MgATPases isolated by different methods

Abstract: Msiribrane bound (Na+ + K+)MgATPases from homogenates of young sugar beet roots were prepared either by differential centrifugations or by an aqueous two-phase system. The properties of the MgATPases were deter- mined in the preparations. Potassium [K (° Rb )] uptake into roots of intact sugar beets was also studied.Preparations, obtained by differential centrifugations, showed different MgATPase properties depending on the presence or absence of sucrose during the preparation. These differences were explained by changes either in sidedness of the membrane vesicles or in conformation of the enzyme structure.Purification by phase partitioning gave a top phase fraction of MgATPase containing vesicles. These were concluded to be plasma membrane vesicles as: 1) the membrane vesicles had a high affinity for the top phase2) practically no mitochondrial membranes were detected in this fraction3) the MgATPase showed a high specificity for ATP 4) the pH dependence of the MgATPase resembled that for other plasma membrane ATPases and5) the MgATPase was inhibited by vanadate but not by oligomycin.1Similarities in pH dependence, potassium activation and synergistic sodium-potassium activation of the MgATPases prepared by differential centrifugations or by phase partitioning inferred that the former was mainly of plasma membrane origin.2+Cadmium(Cd ) uncompetitively inhibited the active (2,4-dinitrophenol- sensitive) potassium uptake into roots and the potassium activation of the plasma menbrane MgATPase. The identical inhibition patterns indicated a connection between the potassium uptake and the MgATPase. Furthermore, the MgATPase was synergistically activated by sodium plus potassium, thus implying a function in a sodium-potassium exchange mechanism between the sugar beet root and its environment.