Denatured proteins as cofactors for plasminogen activation

Raymund Machovich, Whyte G. Owen

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Activation of covalently intact plasminogen by tissue-type plasminogen activator (tPA) is facilitated by a majority of proteins subjected to denaturing conditions. Except for heat-denatured apoferritin, the denatured proteins examined require partial proteolysis by plasmin for cofactor activity. The same proteins in their native state are resistant to proteolysis with plasmin and develop no activity. Denatured preparations of apoferritin, antithrombin, α1-protease inhibitor, α2-macroglobulin, and albumin also accelerate des1-77-plasminogen activation by tPA. The rate enhancements are comparable with that of the fibrin(ogen) fragments on a w/w basis. The cofactor activities are inhibited by 6-aminohexanoate and inactivated by pepsin. Analysis of heat-denatured apoferritin and albumin preparations by ultracentrifugation and gel chromatography indicates that cofactor is associated predominately with aggregates, which have binding capacity for both tPA and zymogen. Heat-denatured albumin pretreated with plasmin decreases K(M) and increases k(cat) for both intact plasminogen and des1-77-plasminogen activation by tPA, yielding catalytic efficiencies in excess of 8 x 103 M-1 s-1 and 2 x 104 M-1 s-1, respectively. Because of enhanced plasmin-catalyzed proteolysis of plasminogen to des1- 77-plasminogen, activation by urokinase-type plasminogen activator is also facilitated by denatured proteins; activation of des1-77-plasminogen is not affected. It is concluded that denatured proteins serve as both cofactors and substrates in the fibrinolytic system, and that enhancement of plasminogen activation by denatured proteins is mechanistically indistinguishable from that observed with fibrin.

Original languageEnglish
Pages (from-to)343-349
Number of pages7
JournalArchives of Biochemistry and Biophysics
Issue number2
Publication statusPublished - Aug 15 1997



  • Fibrinolysis
  • Plasminogen
  • Protein catabolism

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Molecular Biology

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