Gel filtered human platelets contaminated with less than 0.02% of plasma protein S contained 490 ng of protein S antigen per 3 X 10(8) platelets, equivalent to 2.5% of protein S in whole blood. Three patients with heterozygous plasma protein S deficiency, a congenital disorder associated with venous thrombotic disease, had platelet protein S antigen levels that were 40% of the mean platelet level in ten normal volunteers. In immunoblotting analysis, platelet protein S was indistinguishable from plasma protein S. Thrombin stimulation of platelets caused release of 63% of total protein S antigen and this release was abolished when platelets were preincubated with metabolic inhibitors. Thrombin effected limited proteolysis of platelet protein S and this reaction was inhibited by calcium ions. Immunofluorescent staining of platelets using protein S antibodies demonstrated that protein S colocalized with fibrinogen, an established alpha-granule protein. Thus, human platelets contain protein S in alpha granules that can be released by thrombin stimulation. The released protein S may bind to stimulated platelets and thereby promote and localize the anticoagulant activity of activated protein C on the platelet surface.
ARTICLES| December 1, 1985
Identification and quantitation of protein S in human platelets
Blood (1985) 66 (6): 1452-1455.
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HP Schwarz, MJ Heeb, JD Wencel-Drake, JH Griffin; Identification and quantitation of protein S in human platelets. Blood 1985; 66 (6): 1452–1455. doi: https://doi.org/10.1182/blood.V66.6.1452.bloodjournal6661452
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