Stopped-flow fluorescence kinetics of bovine alpha 2-antiplasmin inhibition of bovine midiplasmin.
In the conversion of bovine plasminogen to bovine plasmin not only the expected urokinase-catalysed cleavage of Arg-557-Val-558, and the following autocatalytic cleavage separating the N-terminal peptide 1-77 from the heavy chain of plasmin, but also a cleavage at Arg-342-Met-343 between kringles 3 and 4 is seen. Here, kinetic studies of the interaction of bovine alpha 2-antiplasmin with bovine plasmin were performed on isolated bovine midiplasmin (lacking kringles 1-3) and on bovine plasmin containing all of the activation products from the bovine plasminogen. A series of experiments using stopped-flow fluorescence fast kinetics as well as conventional techniques suggests a reaction model in accordance with the one known for the human system. First, a tight complex (K1 in the nanomolar range) is formed in a fast reaction step; and second, a tightening of this complex occurs in a slow reaction step. The final complex is indeed so tight (Ki < or = pM), that the reaction for many practical purposes is legitimately considered irreversible. The stopped-flow method allows for the determination of reliable values of the second-order rate constant for the fast association step. At pH 7.4 and 25 degrees C, k+1 = 1.7 x 10(6) M-1 s-1 was obtained in the absence and k+1 = 0.9 x 10(6) M-1.s-1 in the presence of the kringles 1-3 domain of bovine plasmin. In contrast to this, substantial reductions of k+1 were seen in the presence of concentrations of 6-amino-hexanoic acid corresponding to lysine-binding-site interactions and far too low to be attributed to active-site interactions with the bovine plasmins (for each, Ki = 42 mM). All in all, the data indicated that the lysine-binding site(s) not of kringle 1, but of midiplasmin (those of kringles 4 and 5) are regulating the inhibition reaction.
Christensen
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S
Department of Molecular Biology, University of Aarhus, Denmark.
Sottrup-Jensen
L
L
Christensen
U
U
D000818:Animals; D000933:Antifibrinolytic Agents; D002417:Cattle; D005341:Fibrinolysin / Q000037:antagonists & inhibitors* / Q000378:metabolism / Q000494:pharmacology*; D005453:Fluorescence; D007700:Kinetics; D018082:Kringles; D010446:Peptide Fragments / Q000037:antagonists & inhibitors*; D010958:Plasminogen / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D014568:Urokinase-Type Plasminogen Activator / Q000378:metabolism; D000979:alpha-2-Antiplasmin / Q000378:metabolism / Q000494:pharmacology*
D000933:Antifibrinolytic Agents; D010446:Peptide Fragments; D000979:alpha-2-Antiplasmin; C019493:miniplasmin; C037742:plasmin-plasmin inhibitor complex; D010958:Plasminogen; D005341:Fibrinolysin; D014568:Urokinase-Type Plasminogen Activator