PMID: 6113237Jun 10, 1981Paper

A spectrin-dependent ATPase of the human erythrocyte membrane.

The Journal of Biological Chemistry
G S Baskin, R G Langdon

Abstract

Removal of spectrin from erythrocyte membranes results in the simultaneous loss of a calcium-stimulated, magnesium-dependent ATPase with an apparent KD for Ca2+ of 1 microM. This ATPase activity with high Ca2+ affinity is specifically reconstituted by addition of purified spectrin to spectrin-depleted membranes, and the reconstituted activity is directly proportional to the amount of spectrin that is reassociated with the membranes. Spectrin binding and activation of the high Ca2+ affinity Mg2+-ATPase are proportionally inhibited by thermal denaturation, trypsin digestion, or treatment of the membranes with thiol-reactive reagents. Binding of calmodulin to the Ca2+ pump ATPase requires that calmodulin contains bound ca2+. By contrast, spectrin binding to the erythrocyte membrane is Ca2+-independent. Direct assay of calmodulin is purified spectrin and absence of chlorpromazine inhibition of reconstitution demonstrate that activation of the high Ca2+ affinity ATPase resulting from spectrin binding is not a result of contamination of spectrin by calmodulin. Additional evidence that the spectrin-activated ATPase is an entity separate and distinct from the Ca2+ pump is provided by other characteristics of the activation phenomenon. ...Continue Reading

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