IN-VITRO INACTIVATION AND STABILIZATION OF FIBRINOLYTIC-ACTIVITY OF UROKINASE

When incubated at 30 degrees C and pH 7.4, urokinase lost fibrinolytic activity (i.e., the plasminogen-activating activity measured by the t ime of fibrin clot lysis) but completely retained amidase activity. Th e enzyme inactivation rate depended on the urokinase concentration and , at concentrations of more than 1.5 mu M, was described by a second o rder equation, which indicated that the enzyme underwent autolytic deg radation (k(aut) = 3.8 x 10(-3) M-1 min(-1)). During incubation, uroki nase (54 kDa) was converted into its low-molecular-mass form (33 kDa) and products of the A-chain degradation. The amidase activity did not correlate with the fibrinolytic activity in the cases when the enzyme molecule underwent local unfolding or partial degradation. The optimum mixture of agents for stabilizing the fibrinolytic activity of urokin ase was found.