title: The mechanism of the reaction between human plasminogen-activator inhibitor 1 and tissue plasminogen activator.
abstract: The structural events taking place during the reaction between PAI-1 (plasminogen-activator inhibitor 1) and the plasminogen activators sc-tPA (single-chain tissue plasminogen activator) and tc-tPA (two-chain tissue plasminogen activator) were studied. Complexes were formed by mixing sc-tPA or tc-tPA with PAI-1 in slight excess (on an activity basis). The complexes were purified from excess PAI-1 by affinity chromatography on fibrin-Sepharose. Examination of the purified complexes by SDS/polyacrylamide-gel electrophoresis (SDS/PAGE) and N-terminal amino acid sequence analysis demonstrated that a stoichiometric 1:1 complex is formed between PAI-1 and both forms of tPA. Data obtained from both complexes revealed the amino acid sequences of the parent molecules and, in addition, a new sequence: Met-Ala-Pro-Glu-Glu-. This sequence is found in the C-terminal portion of the intact PAI-1 molecule and thus locates the reactive centre of PAI-1 to Arg346-Met347. The proteolytic activity of sc-tPA is demonstrated by its capacity to cleave the 'bait' peptide bond in PAI-1. The complexes were inactive and dissociated slowly at physiological pH and ionic strength, but rapidly in aq. NH3 (0.1 mol/l). Amidolytic tPA activity was generated on dissociation of the complexes, corresponding to 0.4 mol of tPA/mol of complex. SDS/PAGE of the dissociated complexes indicated a small decrease in the molecular mass of PAI-1, in agreement with proteolytic cleavage of the 'bait' peptide bond during complex-formation.
authors.affiliation: Department of Clinical Chemistry, Karolinska Hospital, Stockholm, Sweden.
authors.forename: T L
authors.initials: TL
authors.lastname: Lindahl
authors.forename: P I
authors.initials: PI
authors.lastname: Ohlsson
authors.forename: B
authors.initials: B
authors.lastname: Wiman
mesh_terms: D000595:Amino Acid Sequence; D002846:Chromatography, Affinity; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D008969:Molecular Sequence Data; D015849:Plasminogen Inactivators / Q000378:metabolism*; D010959:Tissue Plasminogen Activator / Q000276:immunology / Q000378:metabolism*; D014407:Tumor Cells, Cultured
chemical_list: D015849:Plasminogen Inactivators; D010959:Tissue Plasminogen Activator