The ability of fibrinogens, FI and FII, to support ADP-induced platelet aggregation.

Fibrinogen plays an integral part in ADP-induced platelet aggregation. Controversy exists in regard to the role of the carboxy termini of fibrinogen A alpha chains in this reaction. We have attempted to clarify this problem in view of the availability of a highly purified FII fibrinogen fraction. Kabi fibrinogen or its purified fractions FI, FII and FIII-IV-V were added to washed platelets in the presence of Tyrode-HEPES buffer pH 7.4. Aggregation was initiated by the addition of calcium and ADP. These fibrinogen fractions equally promoted ADP-induced platelet aggregation. The major difference among these fractions is in their A alpha chains. The FI fraction contains intact A alpha chains while FII and FIII-IV-V fractions have one and two partially degraded A alpha chains at the carboxy terminal portion respectively. We conclude that the carboxy terminal portion of the A alpha chain does not play an important role in promoting ADP-induced platelet aggregation.