Thrombin and the thrombin-thrombomodulin complex interaction with plasminogen activator inhibitor type-1.
Thrombin, the final enzyme of the coagulation system, also influences profibrinolytic activity by several mechanisms. These include cellular release of tissue plasminogen activator, activated protein C-induced fibrinolysis, and inactivation of plasminogen activator inhibitor, type 1 (PAI-1). In this report, the role of thrombin in the regulation of PAI-1 is investigated. Our studies demonstrate that thrombin inactivation of PAI-1 occurs via an enzymatic mechanism rather than an enzyme-inhibitor complex mechanism. Evidence to support this conclusion is: (1) concomitant analysis of PAI-1 and thrombin activities demonstrate decreased PAI-1 activity but no loss of thrombin activity; (2) no visible thrombin--PAI-1 complexes by SDS-PAGE analysis; and (3) lack of formation of 125I-thrombin-PAI-1 complexes. Thrombomodulin, a thrombin binding cofactor that modifies thrombin's functions, did not influence the inactivation of PAI-1 by thrombin. We propose that thrombin enzymatically inactivates PAI-1 without forming a stable enzyme-inhibitor complex. The reaction is not affected by thrombomodulin. Overall this reaction occurs so slowly that it is not physiologically relevant without some modifying factor(s).
Madden
R M
RM
Laboratory Services, Denver VA Medical Center, CO 80220.
Levin
E G
EG
Marlar
R A
RA
D000818:Animals; D006801:Humans; D007700:Kinetics; D015849:Plasminogen Inactivators / Q000378:metabolism*; D011817:Rabbits; D011956:Receptors, Cell Surface / Q000378:metabolism*; D018179:Receptors, Thrombin; D013917:Thrombin / Q000378:metabolism / Q000494:pharmacology*
D015849:Plasminogen Inactivators; D011956:Receptors, Cell Surface; D018179:Receptors, Thrombin; D013917:Thrombin