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    J Biol Chem. 2000 Apr 28;275(17):12410-5.

    Inactivation of active thrombin-activable fibrinolysis inhibitor takes place by a process that involves conformational instability rather than proteolytic cleavage.

    Source

    Thrombosis and Haemostasis Laboratory, Department of Haematology, University Medical Center, P.O. Box 85500, 3508 GA Utrecht, The Netherlands. P.F.Marx@lab.azu.nl

    Abstract

    Thrombin-activable fibrinolysis inhibitor (TAFI) is present in the circulation as an inactive zymogen. Thrombin converts TAFI to a carboxypeptidase B-like enzyme (TAFIa) by cleaving at Arg(92) in a process accelerated by the cofactor, thrombomodulin. TAFIa attenuates fibrinolysis. TAFIa can be inactivated by both proteolysis by thrombin and spontaneous temperature-dependent loss of activity. The identity of the thrombin cleavage site responsible for loss of TAFIa activity was suggested to be Arg(330), but site-directed mutagenesis of this residue did not prevent inactivation of TAFIa by thrombin. In this study we followed TAFI activation and TAFIa inactivation by thrombin/thrombomodulin in time and characterized the cleavage pattern of TAFI using matrix-assisted laser desorption ionization mass spectrometry. Mass matching of the fragments revealed that TAFIa was cleaved at Arg(302). Studies of a mutant R302Q-TAFI confirmed identification of this thrombin cleavage site and, furthermore, suggested that inactivation of TAFIa is based on its conformational instability rather than proteolytic cleavage at Arg(302).

    PMID:
    10777524
    [PubMed - indexed for MEDLINE]
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