Modification of high molecular weight plasmic degradation products of human crosslinked fibrin

The predominant high molecular weight products of plasmic digestion of human crosslinked fibrin Fragments DD, E and (DD)E complex were purified by column gel filtration in a non-dissociating buffer or by ion-exchange chromatography on DEAE-cellulose. The structure of the degradation products was studied by proteolytic degradation, polyacrylamide gel electrophoresis immunodiffusion and sucrose density gradient centrifugation. Unaltered derivatives were very resistant to proteolytic degradation by plasmin. In the the presence of 10 mM EDTA the (DD)E complex did not dissociate, but similar to Fragment DD, became susceptible to plasmic degradation forming Fragment D derivatives. The (DD)E complex dissociated in 3 M urea at pH 5.5, had an altered conformation as evidenced by its aggregability and by its increased susceptibility to degradation by plasmin resulting in the formation of Fragment d. The gammagamma chain remnants of Fragment DD were attacked first, followed by cleavage of the beta chain remnants. It is concluded that plasmin resistance is a function of the intact structure and it is not directly dependent on the presence of the crosslink bonds or calcium ions.