Characterization of monoclonal antibodies against human protein C specific for the calcium ion-induced conformation or for the activation peptide region.

Three monoclonal antibodies have been produced that are specific for the activation peptide region in human protein C. These antibodies inhibited the activation of protein C by thrombin and by the thrombin-thrombomodulin complex. A fourth monoclonal antibody specifically recognized the Ca2+-stabilized conformation in protein C. This antibody bound both intact protein C and protein C from which the gamma-carboxyglutamic acid-containing region had been removed by limited proteolysis. These results indicate that this antibody recognizes the conformation in protein C stabilized by Ca2+ bound to the single binding site that is independent of gamma-carboxyglutamic acid.