Ion-translocating ATPases in tendrils of Bryonia dioica Jacq.

Procedures have been developed which allow the preparation of highly pure endoplasmic reticulum and plasma membrane from tendrils of Bryonia dioica. These and further membrane fractions were used to study vanadate-sensitive ATPase activity as well as MgATP-driven transport of Ca. Calcium-translocating ATPases were detected in the endoplasmic reticulum, the plasma membrane and the mitochondrial fraction and characterized kinetically and with respect to the effects of various inhibitors. The endoplasmic-reticulum Ca-translocating ATPase was stimulated by KCl and was calmodulin-dependent. The plasma-membrane enzyme was not affected by these agents. These, as well as the inhibitor data, show that the Ca-translocating ATPases of the endoplasmic reticulum and the plasma membrane are distinctly different enzymes. Upon mechanical stimulation, the activities of the vanadate-sensitive K, Mg-ATPase and the Ca-translocating ATPase(s) increased rapidly and transiently, indicating that increasing transmembrane proton and calcium fluxes are involved in the early stages of tendril coiling. [ABSTRACT FROM AUTHOR]