STABILIZATION OF PLASMIN BY LYSINE DERIVATIVES

Plasmin is a serine protease with trypsin-like specificity and is acti vated from plasminogen by several plasminogen activators. Since plasmi n has lysine binding site in its heavy chain, lysine derivatives react with plasmin and then modify its activity. The effects of lysine deri vatives such as epsilon-aminocaproic acid (EACA) and tranexamic acid o n bovine plasmin activity were investigated. In the absence of lysine derivatives, the bovine plasmin activity which was evaluated as the am idolytic activity was reduced in a time- or temperature-dependent mann er. However, the bovine plasmin activity became stable upon adding EAC A or tranexamic acid. When plasmin was incubated at 4 degrees C for 1, 3 or 5 days without lysine derivatives, the plasmin activity decrease d to 43.9%, 19.9% and 11.9% of the initial activity, respectively. On the other hand, when plasmin was incubated at 37 degrees C for 1, 3 or 5 days with tranexamic acid, its activity remained at 110%, 95.6% and 85.9%, respectively. After bovine plasmin had been incubated for 5 da ys at 4 degrees C in the absence of tranexamic acid, the plasmin activ ity declined to less than 20%. However, when bovine plasmin had been i ncubated for 5 days at 37 degrees C in the presence of tranexamic acid , the residual plasmin activity was more than 80%. A similar effect of EACA on bovine plasmin was observed, but it was weaker than that of t ranexamic acid. Reversed-phase HPLC followed by SDS-PAGE demonstrated that bovine plasmin was degraded into several fragments. Amino acid se quencing of these fragments revealed that the Lys77-Arg78 or Arg78-Ile 79, Arg342-Met343 and Arg557-Ile558 peptide bonds in the bovine plasmi n molecule were cleft, respectively. Only the fragment consisting of t he amino acid region from Met343 to the C-terminal amino acid, Asn786, exhibited amidolytic activity. In proportion to inactivation of the b ovine plasmin, this fragment disappeared. The above findings suggest t hat lysine derivatives react with bovine plasmin and then stabilize th e activity of plasmin by preventing the degradation of active fragment (Met343-Asn786).