Identification and quantitation of protein S in human platelets.
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.
Schwarz
H P
HP
Heeb
M J
MJ
Wencel-Drake
J D
JD
Griffin
J H
JH
D001792:Blood Platelets / Q000032:analysis* / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D006023:Glycoproteins / Q000097:blood*; D006801:Humans; D007457:Iodine Radioisotopes; D017293:Protein S; D013917:Thrombin / Q000494:pharmacology
D006023:Glycoproteins; D007457:Iodine Radioisotopes; D017293:Protein S; D013917:Thrombin