Dissociation of Esterolytic and Clotting Activities of Thrombin by Trypsin-Binding Macroglobulin.

Abstract

Summary Preparations of alpha-2 trypsin-binding macroglobulin purified from Conn Plasma Fraction III-O have been found to bind human and bovine thrombin. The enzyme-macroglobulin complex formed is inactive against fibrinogen but readily hydrolyzes synthetic substrates such as N-p-tosyl-L-arginine methyl ester and N-carbobenzoxy-L-tyrosine p-nitrophenyl ester. Inactivation of thrombin clotting activity by binding to the macroglobulin follows an apparent bimolecular reaction. The complex has been isolated by Sephadex G-100 gel filtration and partial success has been obtained in dissociating the esterase activity but not the clotting activity from the macroglobulin. These findings may have important implications concerning the “binding” or “active site” of the estero-proteolytic activities of thrombin as well as the role which the enzyme-macro-globulin complex may have in blood clotting.