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Reaction of human α 2 ‐antiplasmin and plasmin Stopped‐flow fluorescence kinetics
Author(s) -
Christensen Ulla,
Bangert Kristian,
Thorsen Sixtus
Publication year - 1996
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(96)00429-2
Subject(s) - plasmin , chemistry , kinetics , lysine , enzyme kinetics , binding site , substrate (aquarium) , reaction rate constant , fluorescence , stereochemistry , active site , biochemistry , enzyme , amino acid , biology , ecology , physics , quantum mechanics
The interaction of human plasmin with human α 2 ‐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 α 2 ‐antiplasmin in the absence of another interacting compound, e.g. a plasmin substrate. At pH 7.4,25°C, k 1 = 2.2 X 10 7 M −1 s −1 was obtained. Substantial reductions in k 1 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 α 2 ‐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 α 2 ‐antiplasmin. Similar results were recently obtained for the bovine plasmin‐bovine α 2 ‐antiplasmin reaction (Christensen et al. (1995) Biochem. J. 305, 97–102).