The role of the lysine binding sites of human plasmin in the hydrolysis of human fibrinogen.

The importance of the lysine binding sites of human plasmin for its ability to digest human fibrinogen has been assessed by analyzing the nature and rate of the products formed in the presence of epsilon-aminocaproic acid. No major differences in this regard were found when comparing Lys77-plasmin and Val442-plasmin, in the absence of epsilon-aminocaproic acid, the latter plasmin being devoid of the lysine binding sites present on residues Glu1-Val441 (K 1-4). The presence of epsilon-aminocaproic acid, at concentrations ranging from 0.5-5.0 mM, results in progressively stronger inhibition of the digestion of fibrinogen and in appearance of fibrinogen degradation products Y, D and E, for both Lys77-plasmin, and Val442-plasmin, showing the importance of lysine binding regions in this property. However, since both plasmin forms were inhibited equally well at all levels of epsilon-aminocaproic acid, these studies show that lysine binding sites other than those present on region K 1-4 of Lys77-plasmin are of primary importance to fibrinogenolysis by plasmin.