A kinetic analysis of the tissue plasminogen activator and DSPAalpha1 cofactor activities of untreated and TAFIa-treated soluble fibrin degradation products of varying size.
The kinetics of tissue plasminogen activator (t-PA) and DSPAalpha1-catalyzed plasminogen activation using untreated and TAFIa-treated fibrin degradation products (FDPs), ranging in weight average molecular weight (M(w)) from 0.48 x 10(6) to 4.94 x 10(6) g/mol, were modeled according to the steady-state template model. The FDPs served as effective cofactors for both activators. The intrinsic catalytic efficiencies of both t-PA (17.4 x 10(5) m(-1) s(-1)) and DSPAalpha1 (6.0 x 10(5) m(-1) s(-1)) were independent of FDP M(w). The intrinsic catalytic efficiency of t-PA was 12-fold higher than that measured under identical conditions with intact fibrin as the cofactor. At sub-saturating levels of cofactor and substrate, rates were strongly dependent on FDP M(w) with DSPAalpha1 but not t-PA. Loss of activity with decreasing FDP M(w) correlated with loss of finger-dependent binding of the activators to the FDPs. TAFIa treatment of the FDPs resulted in 90- and 215-fold decreases in the catalytic efficiencies of t-PA (0.20 x 10(5) m(-)(1) s(-1)) and DSPAalpha1 (0.028 x 10(5) m(-1) s(-1)), yielding cofactors that were still 30- and 50-fold better than fibrinogen with t-PA and DSPAalpha1, respectively. Our results show that for both activators the products released during fibrinolysis are very effective cofactors for plasminogen activation, and both t-PA and DSPAalpha1 cofactor activity are strongly down-regulated by TAFIa.
Walker
J B
JB
Departments of Biochemistry and Medicine, Queen's University, Kingston, Ontario K7L 3N6, Canada.
Nesheim
M E
ME
D000818:Animals; D025901:Carboxypeptidase B2; D002268:Carboxypeptidases / Q000378:metabolism*; D002384:Catalysis; D005337:Fibrin / Q000378:metabolism*; D005342:Fibrinolysis / Q000502:physiology; D006801:Humans; D007700:Kinetics; D010446:Peptide Fragments / Q000378:metabolism; D010958:Plasminogen / Q000378:metabolism; D010960:Plasminogen Activators / Q000737:chemistry / Q000378:metabolism*; D012995:Solubility; D010959:Tissue Plasminogen Activator / Q000737:chemistry / Q000378:metabolism*
D010446:Peptide Fragments; C069588:salivary plasminogen activator alpha 1, Desmodus rotundus; D005337:Fibrin; D010958:Plasminogen; D002268:Carboxypeptidases; D025901:Carboxypeptidase B2; D010960:Plasminogen Activators; D010959:Tissue Plasminogen Activator