11] Regulation of Ca2+-pump from cardiac sarcoplasmic reticulum

Abstract

This chapter extensively surveys, and summarizes the technical and procedural aspects, as well as the enzymatic properties of cardiac sarcoplasmic reticulum (SR) Ca2+-pump and its relationship to the putative regulator, phospholamban. Structural and functional aspects of the latter protein are thoroughly reviewed, with emphasis on its regulatory role of the Ca2+-pumping function by SR membranes. Cardiac SR membranes are obtained by differential centrifugation of the homogenate from canine ventricular muscle. SR membranes, largely condensed in the microsomal fraction, are found to form resealed right-side-out vesicles with a diameter of 0.1–0.2 μm. Ca2+-pump ATPase, representing the major protein component within cardiac SR, forms a tight complex with bilayer lipids. Like skeletal SR, cardiac ATPase protein is asymmetrically distributed across the membrane. The ATPase of the cardiac SR is an amphipathic single polypeptide whose hydrophobic region is embedded in the lipid bilayer of the SR membrane and whose hydrophilic region is exposed to the cytoplasmic surface of the SR.