Summary
The interaction of urokinase (EC 3.4.21.31) and a protein proteinase inhibitor of
fibrinolysis partially purified from placental tissue, which inhibits urokinase but
not plasmin, was investigated. The preparations of the inhibitor contained no other
known proteinase inhibitors. It was found that a 1:1 complex is formed and that the
reaction proceeds as a second order, one step process, the association rate constant
of which is 4.5 106 M−1 S−1 at pH 8.4, 37° C and 3.0 106 M−1 S−1 at pH 7.3, 37° C. The binding is very tight, the dissociation constant of the inhibitor-urokinase
complex was estimated to be Ki≦10−11 M.
Keywords
Placental inhibitor of fibrinolysis - Urokinase - Reaction kinetics
