On the Kinetics of the Reaction between Human Antiplasmin and a Low-Molecular-Weight Form of Plasmin

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Abstract
The reaction between antiplasmin (A) and a low-molecular-weight form of plasmin (P) proceeds in at leat two steps: a fast reversible second-order reaction followed by a slower irreversible first-order transition, and may be represented by: The low-Mr plasmin, which is obtained by limited elastase digestion, is composed of an intact B chain and a small A chanin lacking the lysine-binding sites The k1 of the reaction is (6.5 ± 0.5) × 105 M−1 s−1 which is 30–60 times smaller than that for normal plasmin adn antiplasmin. The dissociation constant of the first steip is 1.9 × 10−9 M which is 10 times higher than for normal plasmin and antiplasmin. The rate constant of the second step is (4.2 ± 0.2) × 10−3 s−1 for both normal and low-Mr plasmin. Low Mr plasmin which has substrate bound to its active site does not react or reacts only very slowly with antiplasmin. The reaction rate, however, is only slightly influenced by 6-aminohexaoic acid in concentrawtions up to 1 mM which decrease the reaction rate of normal plasmin approximately 50-fold. The findings further indicate that the lysine-binding site(s) of plasmin are of greaat importance for the rate of its reaction with antiplasmin.