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Effective lysis of model thrombi by a t‐PA mutant (A473S) that is resistant to α 2 ‐antiplasmin
Author(s) -
Robbie L. A.,
Bennett B.,
Keyt B. A.,
Booth N. A.
Publication year - 2000
Publication title -
british journal of haematology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.907
H-Index - 186
eISSN - 1365-2141
pISSN - 0007-1048
DOI - 10.1111/j.1365-2141.2000.02365.x
Subject(s) - lysis , plasminogen activator , fibrinolysis , mutant , microbiology and biotechnology , plasminogen activator inhibitor 1 , wild type , fibrin , chemistry , tissue plasminogen activator , biology , immunology , biochemistry , medicine , endocrinology , gene
This study used two mutants of tissue‐type plasminogen activator (t‐PA) with resistance to inhibitors of fibrinolysis to define the contribution of plasminogen activator inhibitor (PAI)‐1 and α 2 ‐antiplasmin (α 2 ‐AP) to the control of fibrin lysis. Wild‐type t‐PA was compared with KHRR296–299AAAA, which is resistant to PAI‐1, and with A473S, which is resistant to α 2 ‐AP. We examined these forms of t‐PA in model systems that are physiologically relevant. Neutralization of α 2 ‐AP was essential for lysis of plasma clots, irrespective of their platelet content, by either wild‐type t‐PA or KHRR296–299AAAA. In marked contrast, A473S lysed plasma clots without neutralization of α 2 ‐AP. Model thrombi, with structures similar to in vivo thrombi, were lysed slowly by wild‐type t‐PA; the rate and extent of lysis were enhanced by the addition of antibodies to α 2 ‐AP or PAI‐1. A473S was more effective than wild‐type t‐PA without the addition of antibodies by virtue of its resistance to α 2 ‐AP. This resistance was remarkable, in that no complex formed between A473S t‐PA and α 2 ‐AP, even after extended incubation, when 50% of wild‐type t‐PA could be converted to complex. Comparison of A473S and KHRR296–299AAAA mutants showed their similar effectiveness in lysis of platelet‐rich model thrombi. Thus, PAI‐1 and α 2 ‐AP contribute approximately equally to the inhibition of thrombus lysis. This study underlines the functional significance of α 2 ‐AP as a direct inhibitor of t‐PA and further explains the basis of the accepted role of α 2 ‐AP as a regulator of fibrin persistence and thrombus resistance to lysis.