A Ca ⁺⁺ -Dependent and -Selective Ionophore as Part of the Ca ⁺⁺ + Mg ⁺⁺ -Dependent Adenosinetriphosphatase of Sarcoplasmic Reticulum

Abstract

Solubilized Ca(++) + Mg(++)-dependent adenosinetriphosphatase (EC 3.6.1.3; ATP diphosphohydrolase) from sarcoplasmic reticulum increased bimolecular lipid membrane (oxidized cholesterol) conductance several hundred-fold. The relative conductance change and the relative permeability elicited by this material has the following sequence: Ba(++) > Ca(++) > Sr(++) > Mg(++) > Mn(++) > Zn(++), Na(+), K(+), Cs(+), Li(+), and Rb(+). Zn(++) and Na(+) strongly inhibit the increase in Ca(++) conductance obtained with solubilized Ca(++) + Mg(++)-dependent adenosinetriphosphatase. The Ca(++)-ionophore is an integral part of the Ca(++) + Mg(++)-dependent adenosinetriphosphatase enzyme and may function as a Ca(++)-carrier in the overall Ca(++)-pump of sarcoplasmic reticulum.