The effect of plasmin on the subunit structure of human fibrin.

Non-cross-linked, partially cross-linked, and highly crosslinked human fibrin were each digested with plasmin and the changes in the subunit structures of the degradation products were followed sequentially by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The digestion products of non-cross-linked fibrin were similar to those previously reported for fibrinogen. The digestion products of partially and highly cross-linked fibrin differed somewhat from those of fibrinogen. The a(A) chains of fibrinogen and the (Y chains of non-cross-linked and partially cross-linked fibrin were degraded rapidly to give low molecular weight peptides. The OL polymers of highly cross-linked fibrin were degraded more slowly but also yielded low molecular weight peptides which probably contained cross-links. The /3(B) chain of fibrinogen and the /3 chain in all three types of fibrin yielded a terminal digestion product with a molecular weight of about 44,500. The major digestion products of the y chains of fibrinogen and non-cross-linked fibrin are identical and have molecular weights between 27,000 and 42,000. In contrast, cross-linked y chains are degraded to a species with a molecular weight of 81,000. Fragment E from fibrinogen and Fragment E from fibrin were structurally very similar. Fragment D from fibrinogen and fibrin, however, differed in structure. Structural analyses of the degradation products, which appear during digestion of non-cross-linked, partially cross-linked, and highly cross-linked fibrin, reveal the major features of the digestion pattern of highly cross-linked fibrin by plasmin.