Thromb Haemost 1994; 72(06): 947-956
DOI: 10.1055/s-0038-1648989
Original Article
Schattauer GmbH Stuttgart

Thrombin-stimulated Human Platelets Express Molecular Forms of α-Granule Factor V (FV), which Differ from FVa

Edward G Wyshock
The Sol Sherry Thrombosis Research Center, Temple University School of Medicine, Philadelphia, PA, USA
,
Gwendolyn J Stewart
The Sol Sherry Thrombosis Research Center, Temple University School of Medicine, Philadelphia, PA, USA
,
Robert W Colman
The Sol Sherry Thrombosis Research Center, Temple University School of Medicine, Philadelphia, PA, USA
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Publikationsverlauf

Received 06. Juni 1994

Accepted after revision 18. August 1994

Publikationsdatum:
06. Juli 2018 (online)

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Summary

Binding of 125I-Fab fragments of chain-specific antibodies indicate that both heavy and light chains of a-granule factor Va (FVa) were externalized on the platelet membrane after stimulation with thrombin. Using a Mab against the activation peptide of factor V (FV), the epitope appears on the stimulated platelet surface. Half as much light chain and heavy chain (FVa) was expressed compared to the activation peptide, suggesting that expression of α-granule FV occurs after thrombin stimulation. Using an ELISA, we find that 32% of a-granule FV was released and 68% is retained in the platelet pellet. Immunoblots of platelets indicate that FV exists in 200 kDa und 150 kDa forms, representing incomplete cleavage, while the releasate demonstrates a more complete cleavage by proteases. We conclude that expression of α-granule FV is quantitatively greater than that released and exists in molecular forms which cannot be completely explained by the binding of FVa.