The ability of fibrinogen fragments to support ADP-induced platelet aggregation

Abstract Plasmin digests of fibrinogen were examined for their ability to support the ADP-induced aggregation of washed human platelets. The extent of aggregation decreased progressively during digestion, but the major loss in activity appeared to occur as fragment X was converted to fragments Y, D and E. In contrast, the thrombin clotting time and staphylococcal cell clumping titre showed immediate and marked changes during the formation of fragment X. These changes are consistent with the loss of essential residues from the C00H-terminal region of the Aα chain early in the proteolysis of fibrinogen by plasmin. The progressive decrease in platelet aggregation, and the absence of intact Aα chain in highly active fragments, however, argues against the critical involvement of the C00H-terminus of the Aα chain in the interaction of fibrinogen with platelets.