Thrombin-activable fibrinolysis inhibitor attenuates (DD)E-mediated stimulation of plasminogen activation by reducing the affinity of (DD)E for tissue plasminogen activator. A potential mechanism for enhancing the fibrin specificity of tissue plasminogen activator.
A complex of d-dimer noncovalently associated with fragment E ((DD)E), a degradation product of cross-linked fibrin that binds tissue plasminogen activator (t-PA) and plasminogen (Pg) with affinities similar to those of fibrin, compromises the fibrin specificity of t-PA by stimulating systemic Pg activation. In this study, we examined the effect of thrombin-activable fibrinolysis inhibitor (TAFI), a latent carboxypeptidase B (CPB)-like enzyme, on the stimulatory activity of (DD)E. Incubation of (DD)E with activated TAFI (TAFIa) or CPB (a) produces a 96% reduction in the capacity of (DD)E to stimulate t-PA-mediated activation of Glu- or Lys-Pg by reducing k(cat) and increasing K(m) for the reaction; (b) induces the release of 8 mol of lysine/mol of (DD)E, although most of the stimulatory activity is lost after release of only 4 mol of lysine/mol (DD)E; and (c) reduces the affinity of (DD)E for Glu-Pg, Lys-Pg, and t-PA by 2-, 4-, and 160-fold, respectively. Because TAFIa- or CPB-exposed (DD)E produces little stimulation of Glu-Pg activation by t-PA, (DD)E is not degraded into fragment E and d-dimer, the latter of which has been reported to impair fibrin polymerization. These data suggest a novel role for TAFIa. By attenuating systemic Pg activation by (DD)E, TAFIa renders t-PA more fibrin-specific.
Stewart
R J
RJ
Hamilton Civic Hospitals Research Centre and McMaster University, Hamilton, Ontario L8V 1C3, Canada.
Fredenburgh
J C
JC
Rischke
J A
JA
Bajzar
L
L
Weitz
J I
JI
D000590:Amino Acid Chloromethyl Ketones / Q000378:metabolism; D001120:Arginine / Q000378:metabolism; D043424:Carboxypeptidase B; D025901:Carboxypeptidase B2; D002268:Carboxypeptidases / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D005337:Fibrin / Q000378:metabolism*; D005338:Fibrin Fibrinogen Degradation Products / Q000378:metabolism*; D005341:Fibrinolysin / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008239:Lysine / Q000378:metabolism; D008956:Models, Chemical; D010959:Tissue Plasminogen Activator / Q000378:metabolism*
D000590:Amino Acid Chloromethyl Ketones; D005338:Fibrin Fibrinogen Degradation Products; C036309:fibrin fragment D; C072054:fibrin fragment E-2; D005337:Fibrin; D001120:Arginine; D002268:Carboxypeptidases; D043424:Carboxypeptidase B; D025901:Carboxypeptidase B2; D010959:Tissue Plasminogen Activator; D005341:Fibrinolysin; D008239:Lysine; C040308:phenylalanyl-prolyl-arginine-chloromethyl ketone