A water-extractable Ca2+-atpase from erythrocyte membranes.

The Ca2+- and Mg2+-stimulated ATPase activities present in low ionic strength extracts of erythrocyte membranes have been separated from each other. The Ca2+-ATPase appears to be associated with particulate meterial which could be sedimented by high-speed centrifugation. The pellet obtained was composed mainly of components 1, 2, 4.5, 5 and 7. A soluble protein from the band 3 region, known to be responsible for the Mg2+-ATPase activity, was not detected in this pellet.