title: Activation of the Ca2+-ATPase of human erythrocyte membrane by an endogenous Ca2+-dependent neutral protease.
abstract: Limited proteolysis of the plasma membrane calcium transport ATPase (Ca2+-ATPase) from human erythrocytes by trypsin produces a calmodulin-like activation of its ATP hydrolytic activity and abolishes its calmodulin sensitivity. We now demonstrate a similar kind of activation of the human erythrocyte membrane Ca2+-ATPase by calpain (calcium-dependent neutral protease) isolated from the human red cell cytosol. Upon incubation of red blood cell membranes with purified calpain in the presence of Ca2+ the membrane-bound Ca2+-ATPase activity was increased and its sensitivity to calmodulin was lost. In contrast to the action of other proteases tested, proteolysis by calpain favors activation over inactivation of the Ca2+-ATPase activity, except at calpain concentrations more than 2 orders of magnitude higher. Exogenous calmodulin protects the Ca2+-ATPase against calpain-mediated activation at concentrations which also activate the Ca2+-ATPase activity. Calcium-dependent proteolytic modification of the Ca2+-ATPase could provide a mechanism for the irreversible activation of the membrane-bound enzyme.
authors.affiliation: Laboratory of Molecular Pharmacology, Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, Canada.
authors.forename: K K
authors.initials: KK
authors.lastname: Wang
authors.forename: A
authors.initials: A
authors.lastname: Villalobo
authors.forename: B D
authors.initials: BD
authors.lastname: Roufogalis
mesh_terms: D000252:Calcium-Transporting ATPases / Q000097:blood*; D002147:Calmodulin / Q000494:pharmacology; D002154:Calpain / Q000097:blood / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D004910:Erythrocyte Membrane / Q000201:enzymology*; D006801:Humans; D008970:Molecular Weight; D010206:Papain / Q000494:pharmacology; D014357:Trypsin / Q000494:pharmacology
chemical_list: D002147:Calmodulin; D014357:Trypsin; D002154:Calpain; D010206:Papain; D000252:Calcium-Transporting ATPases