The role of carbohydrate side chains of plasminogen in its activation by staphylokinase

Kinetic parameters (kPg and KPg) were determined for activation of Glu-plasminogen (Glu-Pg) and Lys-plasminogen (Lys-Pg) type I (with N-linked carbohydrate chain at Asn-289) and type II (with unsubstituted Asn-289) by plasmin-staphylokinase (Pm-STA) complex. The KPg values for Glu-Pg I and Lys-Pg I (17.1 and 11.2 μM, respectively) were higher than those for Glu-Pg II and Lys-Pg II (14.9 and 5.4 μM, respectively), while only minor differences in the kPg values were observed between plasminogens type I and type II. Soluble fibrin significantly increased the kPg/KPg values for activation of all four plasminogens due to a decrease in the KPg values but did not alter the kPg values. However, the activation of plasminogens type I was stimulated by fibrin lesser degree than that of plasminogens type II. These findings indicate that N-glycosylation of kringle 3 of plasminogen decreases the stability of Pm-STA-Pg ternary enzyme-substrate complex in solution as well as interferes with its formation and rearrangement on the fibrin surface.