title: Dissociation of the glycoprotein IIb-IIIa complex in isolated human platelet membranes. Dependence of pH divalent cations.
abstract: The platelet membrane glycoproteins IIb and IIIa normally exist as a complex which forms a predominant immunoprecipitate after crossed immunoelectrophoresis of Triton-X-100-solubilized platelets. Dissociation of the complex occurs by solubilization in the presence of EDTA or EGTA at pH 8.7 and is readily verified by crossed immunoelectrophoresis. Incubations of isolated membranes with EDTA or EGTA at various pH levels were performed. Removal of the chelators and solubilization showed no dissociation of the glycoprotein IIb-IIIa complex in membranes incubated at pH below 8.0. At pH above 8.0 a dissociation which increased with increasing pH was seen. Under these conditions, dissociation appears to take place already in the intact membranes. The tendency of the glycoprotein IIb-IIIa complex to become dissociated with EDTA or EGTA at increasing pH seems to be due to increased chelating capacity of the chelators concomitant with a decreased chelating capacity of glycoprotein IIb and IIIa. The divalent cations Ca2+ and Mg2+, but not Cu2+, Zn2+, Mn2+ or Sr2+, in molar concentrations below that of EGTA were able to prevent the dissociation of the glycoprotein IIb-IIIa complex by the chelator at pH 9.0, indicating that Ca2+ as well as Mg2+ can be used to keep the complex together. In some experiments it was possible to reverse the dissociation in the membranes after removal of EDTA. At pH 7.5 reassociation occurred within 15 min whether divalent cations were added or not. At pH 9.0. reassociation occurred within 2 h provided Ca2+ was present. The tendency of glycoprotein IIb and IIIa to form a complex thus appeared to be most pronounced over the physiological pH range and to be a rapid process in platelet membranes under such conditions.
mesh_terms: D001792:Blood Platelets / Q000032:analysis* / Q000187:drug effects / Q000648:ultrastructure; D002413:Cations, Divalent; D002462:Cell Membrane / Q000187:drug effects / Q000648:ultrastructure; D004492:Edetic Acid / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D006023:Glycoproteins / Q000302:isolation & purification* / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007123:Immunoelectrophoresis, Two-Dimensional; D046911:Macromolecular Substances; D010980:Platelet Membrane Glycoproteins
chemical_list: D002413:Cations, Divalent; D006023:Glycoproteins; D046911:Macromolecular Substances; D010980:Platelet Membrane Glycoproteins; D004533:Egtazic Acid; D004492:Edetic Acid