The action of plasmin on fibrinogen and fibrin I. Changes in the N-Terminal residues

Abstract Changes in the N-terminal amino acids of bovine and human fibrinogen and fibrin resulting from the action of plasmin (EC 3.4.4..14) on these protinens have been studied. Only the N-terminal amino acids of those protein fractions whose phenylthiocarbamyl derivatives are insoluble in acetone-water have been measured. Plasminolysis of the bovine and human proteins leads to similarities and differences in the relative rates at which N-termnial residues appear. Possible causes for these differences are discussed. The observations explain in part the presence of extraneous N-terminal residues frequently found in fibrinogen, particularly if isolated from aged Fraction I preparations, and provide preliminary information which may be useful as a guide during the separation of fragments formed during the proteolysis of fibrinogen.