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

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: (Formula Presented.) 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. Copyright © 1978, Wiley Blackwell. All rights reserved