Anticoagulant And Calcium-Binding Properties Of High Molecular Weight Derivatives Of Human Fibrinogen, Produced By Plasmin (Fragments X)

Early plasmin degradation products (fragments X) of human fibrinogen were prepared and purified on Sepharose 6B-CL. X-fragments were characterized with respect to amino-terminal amino acid sequences, polypeptide-chain composition, anticlotting properties and calcium-binding. Amino-terminal amino acids were alanine and tyrosine. The molecular weights of the chains were about 26,000, 58,000 and 48,000 for Aα-, Bβ- and γ-chains, respectively. Fragments X were about 6 times as potent in anticlotting behaviour as D-fragments prepared in the presence of calcium ions. Calcium-binding properties were similar to those of fibrinogen: No differences were observed between fragments X prepared in the presence of calcium ions and those prepared in the presence of EGTA. Results indicate that the carboxy-terminal parts of the Aα-chains of fibrinogen are not involved in calcium-binding and that differences in chain-remnants as observed in late plasmic degradation products (which depend on the presence of calcium ions or EGTA in the incubation medium) are introduced beyond the stage of fragment X-formation.