Calcium-promoted aggregation of erythrocyte membrane proteins.

Introduction of Ca2+ (greater than 1 mM) into erythrocytes during hemolysis causes formation of an aggregate which is highly resistant to disruption by sodium dodecyl-sulfate and other denaturing agents. The process is temperature dependent, but it does not require incubation in isotonic medium. Aggregation can be prevented but not reversed with chelating agents such as ATP or EDTA. The aggregate can be isolated by chromatography in dodecylsulfate on Sepharose 4B. Its amino acid composition indicates that it contains spectrin as the primary, but not exclusive, polypeptide component. Aggregate formation does not require increased Ca2+ binding to the membranes, and no 45Ca2+ could be detected in the aggregate which had been separated by acrylamide electrophoresis on sodium dodecylsulfate. This indicates that the Ca2+ is important in the formation of the aggregate, but not in its stabilization or maintenance once it has been formed.