title: Persistent Ca2(+)-induced activation of erythrocyte membrane Ca2(+)-ATPase unrelated to calpain proteolysis.
abstract: Preincubation of human erythrocyte membranes with calcium in the submillimolar to millimolar concentration range resulted in an increase of the Ca2+ affinity and apparent maximum velocity of the Ca2(+)-stimulated Mg2(+)-dependent ATPase (Ca2(+)-ATPase). The activation was persistent, as it was not reversed when the Ca2(+)-preincubated membranes were washed with ethylene glycol bis(beta-aminoethyl ether) N,N'-tetraacetic acid-containing buffers. Magnesium was not required for the activation, whereas greater than 2 mM Mg2+ partially antagonized the activation by Ca2+. In some membrane preparations ATP was required in addition to Ca2+ for activation of the Ca2(+)-ATPase, but nonhydrolyzable analogs of ATP had the same effect. Calmodulin prevented the activation by Ca2+ over the same concentration range in which it interacts with the Ca2(+)-ATPase. Taken together the results obtained provided strong evidence that the Ca2+ activation of the enzyme was not due to proteolytic cleavage by endogenous calpain. Thus, activation by Ca2+ was not blocked by leupeptin (100-200 microM), did not require dithiothreitol, and occurred at Ca2+ concentrations greater than those required for activation of calpain I. Furthermore, Ca2+ activation did not result in change in the mobility the native 136-kDa species of the Ca2(+)-ATPase on SDS-gel electrophoresis. Moreover, solubilization of the Ca2(+)-pretreated membranes with Triton X-100 reversed the Ca2+ activation of the Ca2(+)-ATPase. On the other hand, Ca2(+)-pretreatment of the membranes modified the susceptibility of the Ca2(+)-ATPase to both cleavage and activation by exogenously added calpain I. We conclude that pretreatment of Ca2(+)-ATPase in erythrocyte membranes with millimolar Ca2+ activates the enzyme by inducing a persistent conformational change of the enzyme which is, however, subsequently reversed by detergent solubilization.
authors: Department of Biochemistry, University of Sydney, NSW, Australia.
authors: B D
authors: BD
authors: Roufogalis
authors: I
authors: I
authors: Brzuszczak
authors: A D
authors: AD
authors: Conigrave
authors: Y H
authors: YH
authors: Xu
authors: C L
authors: CL
authors: Machan
authors: K K
authors: KK
authors: Wang
mesh_terms: D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002154:Calpain / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D004910:Erythrocyte Membrane / Q000187:drug effects / Q000201:enzymology*; D006801:Humans; D008954:Models, Biological; D017830:Octoxynol; D010766:Phosphorylation; D011092:Polyethylene Glycols / Q000494:pharmacology; D011489:Protein Denaturation; D012995:Solubility
chemical_list: D011092:Polyethylene Glycols; D000255:Adenosine Triphosphate; D017830:Octoxynol; D002154:Calpain; D000252:Calcium-Transporting ATPases; D002118:Calcium