title: A spectrin-dependent ATPase of the human erythrocyte membrane.
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. It is suggested that spectrin constitutes part of an ATPase which may function as a component of the "cytoskeleton" controlling erythrocyte shape and membrane flexibility.
mesh_terms: D000251:Adenosine Triphosphatases / Q000097:blood*; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases / Q000097:blood; D004789:Enzyme Activation; D004910:Erythrocyte Membrane / Q000378:metabolism*; D004912:Erythrocytes / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008565:Membrane Proteins / Q000378:metabolism*; D013049:Spectrin / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D008565:Membrane Proteins; D013049:Spectrin; D000251:Adenosine Triphosphatases; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases