Primary soluble plasmic degradation product of human cross-linked fibrin. Isolation and stoichiometry of the (DD)E complex.

The formation of the (DD)E complex and fragments DD and E upon proteolysis of human cross-linked fibrin was studied by timed digestions using varying amounts of plasmin. The (DD)E complex was the primary soluble degradation product released form cross-linked fibrin. This complex contained fragments DD and E1. Upon further digestion (DD)E1 complex was cleaved to (DD)E2 complex whereby only the fragment E moiety was affected. However, when fragment E2 was digested to fragment E3, dissociation of the complex occurred. Thus, fragments DD and E3 are the terminal plasmic digestion products of cross-linked fibrin. This pattern was consistent regardless of the plasmin to fibrin ratio; however, the rate of production of the terminal degradation products was directly dependent upon enzyme concentration. Digestion conditions were modified so that either the (DD)E complex or fragment DD was the predominant degradation product, allowing for the purification of these species by one-step gel filtration. The molar ratio of fragment DD to fragment E in the (DD)E complex was investigated by dissociation of the complex and by reassociation of the purified components. The (DD)E complex contains one molecule of fragment DD and one molecule of fragment E.