title: The calcium-dependent neutral protease of human blood platelets: a comparison of its effects on the receptors for von Willebrand factor and for the Fc-fragment derived from IgG.
abstract: Glycocalicin (Gc) is the large, water soluble fragment, obtained by cleavage of one of the major membrane glycoproteins, GP Ib, of human platelets by means of the endogenous, calcium-dependent neutral protease (CNP) obtained from lysed platelets. GP Ib has been proposed as the receptor for von Willebrand factor (vWF) as well as for the Fc-receptor of the platelet surface. We have investigated, whether Gc was involved in a receptor function for aggregated human IgG, which is a powerful activator of platelets. Neither Gc nor asialo-Gc inhibited the stimulation of human blood platelets by bisdiazoniumbenzidine-aggregated human IgG (BDB-IgG). Moreover, platelets, after treatment with a crude preparation of CNP, which removes Gc, could be stimulated by BDB-IgG as well as or better than control platelets, but were unreactive with bovine vWF. We conclude that the Gc-moiety of GP Ib, which is involved in the bovine vWF binding site, is not the Fc-receptor on platelets. Thus, the inhibition, by human or rabbit IgG aggregates or monomeric rabbit IgG, of vWF-induced platelet agglutination, as reported by other authors, is either due to a steric effect resulting from a vicinal position of both receptors or involves the residual part of GP Ib after cleavage of Gc.
mesh_terms: D000818:Animals; D001779:Blood Coagulation Factors / Q000378:metabolism*; D001792:Blood Platelets / Q000201:enzymology* / Q000378:metabolism; D002118:Calcium / Q000494:pharmacology*; D002417:Cattle; D010450:Endopeptidases / Q000097:blood*; D006801:Humans; D007141:Immunoglobulin Fc Fragments; D007074:Immunoglobulin G; D007700:Kinetics; D015260:Neprilysin; D010980:Platelet Membrane Glycoproteins; D011956:Receptors, Cell Surface / Q000378:metabolism*; D011961:Receptors, Fc / Q000378:metabolism*; D014841:von Willebrand Factor / Q000378:metabolism*
chemical_list: D001779:Blood Coagulation Factors; D007141:Immunoglobulin Fc Fragments; D007074:Immunoglobulin G; D010980:Platelet Membrane Glycoproteins; D011956:Receptors, Cell Surface; D011961:Receptors, Fc; D014841:von Willebrand Factor; C028254:von Willebrand factor receptor; D010450:Endopeptidases; D015260:Neprilysin; D002118:Calcium