ADENOSINE TRIPHOSPHATE-LINKED CONCENTRATION OF CALCIUM IONS IN A PARTICULATE FRACTION OF RABBIT MUSCLE

Abstract
ATPase and ATP-dependent Ca++ ion concentration was studied with a membrane fraction isolated from homogenized rabbit skeletal muscle by differential centrifugation. Electron micrographs of the fraction indicate that it consists mainly of resealed tubules and vesicles of the endoplasmic reticulum. The up-to-1400-fold concentration of Ca++ in this fraction might be explained by proposing the existence of an energy-requiring system for the transport of Ca++ ions into the tubules or vesicles.