Kinetic analysis of the interaction between plasminogen activator inhibitor-1 and tissue-type plasminogen activator.
The kinetics of inhibition of tissue-type plasminogen activator (t-PA) by the fast-acting plasminogen activator inhibitor-1 (PAI-1) was investigated in homogeneous (plasma) and heterogeneous (solid-phase fibrin) systems by using radioisotopic and spectrophotometric analysis. It is demonstrated that fibrin-bound t-PA is protected from inhibition by PAI-1, whereas t-PA in soluble phase is rapidly inhibited (K1 = 10(7) M-1.s-1) even in the presence of 2 microM-plasminogen. The inhibitor interferes with the binding of t-PA to fibrin in a competitive manner. As a consequence the Kd of t-PA for fibrin (1.2 +/- 0.4 nM) increases and the maximal velocity of plasminogen activation by fibrin-bound t-PA is not modified. From the plot of the apparent Kd versus the concentration of PAI-1 a Ki value of 1.3 +/- 0.3 nM was calculated. The quasi-similar values for the dissociation constants between fibrin and t-PA (Kd) and between PAI-1 and t-PA (Ki), as well as the competitive type of inhibition observed, indicate that the fibrinolytic activity of human plasma may be the result of an equilibrium distribution of t-PA between both the amount of fibrin generated and the concentration of circulating inhibitor.
Masson
C
C
I.N.S.E.R.M. U. 143, Institut de Pathologie Cellulaire, Hôpital de Bicêtre, France.
Angles-Cano
E
E
D002478:Cells, Cultured; D004591:Electrophoresis, Polyacrylamide Gel; D004727:Endothelium / Q000378:metabolism; D005337:Fibrin / Q000378:metabolism; D006023:Glycoproteins / Q000494:pharmacology*; D006801:Humans; D007700:Kinetics; D046911:Macromolecular Substances; D010958:Plasminogen / Q000378:metabolism; D015849:Plasminogen Inactivators; D010959:Tissue Plasminogen Activator / Q000037:antagonists & inhibitors*
D006023:Glycoproteins; D046911:Macromolecular Substances; D015849:Plasminogen Inactivators; D005337:Fibrin; D010958:Plasminogen; D010959:Tissue Plasminogen Activator