ROLE OF THE KRINGLE DOMAIN IN PLASMINOGEN ACTIVATION WITH STAPHYLOKINASE

We have evaluated the effect of lysine binding sites in krigle structu res on the activation of plasminogen with plasmin and staphylokinase ( SAK) complex and on the binding of plasminogen to SAK, Activation of n ative plasminogen (Glu-plasminogen) by a catalytic amount of plasmin-S AK complex increased in the presence of epsilon-amino-n-caproic acid ( EACA) and then decreased with higher concentrations of EACA, By contra st, activation of modified plasminogen (Lys-plasminogen) decreased in an EACA-concentration-dependent manner, This decrease was explained by a more than 10-fold higher K-m for activation of Lys-plasminogen with a catalytic amount of plasmin-SAK complex in the presence of EACA, EA CA was a competitive inhibitor with K-i 0.23mM. In addition, the K-m f or activation of mini-plasminogen, which lacks first four kringle stru ctures (K1+2+3+4), was at least 3.5-fold higher than that for the acti vation of Lys-plasminogen. Furthermore, EACA showed a negligible inhib itory effect on the activation of mini-plasminogen by the plasmin-SAK complex, We observed a similar biphasic effect of EACA on the binding of Glu-plasminogen to SAK and a dose-dependent effect on the Lys-plasm inogen binding to SAK by gel filtration methods, Since EACA binds to p lasminogen via lysine binding sites in the kringle structure, we propo se that the lysine binding site in K1+2+3+4 domain plays a role in the activation of plasminogen by plasmin-SAK complex, and in the binding of plasminogen to SAK.