Fibrinogen fragment D is a recognition site for release-related platelet aggregation

The present study probes for the segment of the fibrinogen molecule which interacts with the platelet surface upon induction of release-related aggregation. The capability of platelets affixed with fibrinogen fragment D or fibrinogen fragment E to enhance aggregation of gel-filtered platelets (GFP) was compared with that of platelets affixed with fibrinogen. It is shown that release-related aggregation induced by either A23187, 10 μM ADP or thrombin is enhanced by the addition of fixed platelets bearing covalently bound fragment D by as much as 60-70% of the augmentation obtained by platelets bearing fibrinogen. On the other hand, fixed platelets bearing covalently-bound fragment E have no effect on the aggregation of GFP. It is concluded that fragment D bears the site for the interaction of fibrinogen with activated platelets, apparently, with surface-bound thrombospondin.