ACTIVATION OF THE CA2+-MG2+-ATPASE BY CA-EGTA IN PLASMALEMMA FROM THE ROOTS OF CUCUMBER

High Ca2+-Mg2+-ATPase activity was demonstrated in the plasmalemma purified by aqueous two-phase partitioning from cucumber roots using Ca-EGTA buffer system. Maximal activity was obtained at pH 7.5 and in the presence of 0.6-2.0-mu-M of free Ca2+. It was stimulated by calmodulin in a dose-dependent manner and by A23 178, and inhibited by calmodulin antagonists, nifedipine, vanadate and N,N'-dicyclohexylcarbodiimide. The response of the Ca2+-Mg2+-ATPase towards calmodulin decreased in Ca2+ deficient plants but it was restored by the pretreatment and treatment with benzyladenine of the plants prior and during Ca2+ deprivation. The use of the Ca-EGTA buffer opens the way for the detailed investigation of the Ca2+-Mg2+-ATPase.