title: On the molecular interactions between plasminogen-staphylokinase, alpha 2-antiplasmin and fibrin.
abstract: The molecular interactions between the plasminogen-staphylokinase complex, alpha 2-antiplasmin and fibrin were studied by measuring the effect of CNBr-digested fibrinogen on the inhibition rate of the plasminogen-staphylokinase complex by alpha 2-antiplasmin. The second-order rate constant for the inhibition of plasminogen-staphylokinase by alpha 2-antiplasmin was 2.7 +/- 0.3.10(6) M-1 s-1 (mean +/- S.D.; n = 7). Addition of CNBr-digested fibrinogen, but not of fibrinogen, resulted in a concentration-dependent reduction of the apparent inhibition rate constant, with a 50 percent reduction at a concentration of 5 nM CNBr-digested fibrinogen. The second-order rate constant for the inhibition of the low-Mr plasminogen-staphylokinase complex (plasminogen lacking the kringle structures comprising the lysine-binding sites) by alpha 2-antiplasmin was about 30-fold lower (9.3 +/- 0.7.10(4) M-1 s-1, mean +/- S.D.; n = 4) than that of plasminogen-staphylokinase and was not affected by addition of CNBr-digested fibrinogen. Inhibition of the plasminogen-staphylokinase complex by the chloromethylketone D-Val-Phe-Lys-Ch2Cl is 9-fold less efficient than that of plasmin (k2/Ki of 700 M-1 s-1 versus 6300 M-1 s-1). Our results confirm and establish that rapid inhibition of plasminogen-staphylokinase by alpha 2-antiplasmin requires the availability of the lysine-binding sites in the plasminogen moiety of the complex. Fibrin, but not fibrinogen, reduces the inhibition rate by alpha 2-antiplasmin by competition for interaction with the lysine-binding site. Protection of the plasminogen-staphylokinase complex bound to fibrin from rapid inhibition by alpha 2-antiplasmin thus appears to contribute to the fibrin-specificity of clot lysis with staphylokinase in a plasma milieu, by allowing preferential plasminogen activation at the fibrin surface, while the free complex is rapidly inhibited in plasma.
authors.affiliation: Center for Thrombosis and Vascular Research, University of Leuven, Belgium.
authors.forename: H R
authors.initials: HR
authors.lastname: Lijnen
authors.forename: B
authors.initials: B
authors.lastname: Van Hoef
authors.forename: O
authors.initials: O
authors.lastname: Matsuo
authors.forename: D
authors.initials: D
authors.lastname: Collen
mesh_terms: D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D003488:Cyanogen Bromide; D005337:Fibrin / Q000378:metabolism*; D005340:Fibrinogen / Q000378:metabolism; D006801:Humans; D008666:Metalloendopeptidases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010958:Plasminogen / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000979:alpha-2-Antiplasmin / Q000378:metabolism*
chemical_list: D000590:Amino Acid Chloromethyl Ketones; D000979:alpha-2-Antiplasmin; C072327:valyl-phenylalanyl-lysine chloromethyl ketone; D005337:Fibrin; D005340:Fibrinogen; D010958:Plasminogen; D008666:Metalloendopeptidases; C022653:auR protein, Staphylococcus aureus; D003488:Cyanogen Bromide