Reaction of human alpha2-antiplasmin and plasmin stopped-flow fluorescence kinetics.
The interaction of human plasmin with human alpha2-antiplasmin was measured in the presence and absence of lysine-binding ligands using the corresponding active site fluorescence changes. The stopped-flow method allows for direct determination of reliable values of the second order rate constant for the fast association step of plasmin and alpha2-antiplasmin in the absence of another interacting compound, e.g. a plasmin substrate. At pH 7.4, 25 degrees C, k1 = 2.2 x 10(7) M(-1)s(-1) was obtained. Substantial reductions in k1 were seen in the presence of trans-4-(aminomethyl)cyclohexane-1-carboxylic acid at concentrations corresponding to lysine-binding site interactions at kringle 4 of plasmin; at saturation the rate constant is reduced 20-fold, whereas the effect of saturation of kringle 1 is only a 2-fold reduction. It is thus found that the interaction of alpha2-antiplasmin with the lysine-binding site of kringle 1 is of little importance compared with that of kringle 4 in regulating the inhibition reaction of plasmin with alpha2-antiplasmin. Similar results were recently obtained for the bovine plasmin-bovine alpha2-antiplasmin reaction (Christensen et al. (1995) Biochem. J. 305, 97-102).
Christensen
U
U
Chemical Laboratory IV, University of Copenhagen, Denmark.
Bangert
K
K
Thorsen
S
S
D000595:Amino Acid Sequence; D005341:Fibrinolysin / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D018082:Kringles; D008958:Models, Molecular; D008969:Molecular Sequence Data; D013050:Spectrometry, Fluorescence; D000979:alpha-2-Antiplasmin / Q000378:metabolism*
D000979:alpha-2-Antiplasmin; D005341:Fibrinolysin