Interaction of annexin V and platelets: effects on platelet function and protein S binding.
Intact annexin V but not its fragments bound specifically to platelets in the presence of calcium. Maximal binding observed was 0.87 pmole annexin V per 10(8) platelets with an apparent dissociation constant of 2.13 x 10(-11) M. This represents approximately 5000 binding sites per platelet. Platelet stimulation by thrombin increased the binding of annexin V by 40-fold. Addition of phospholipid vesicles or treatment with phospholipase C inhibited annexin V binding to platelets, suggesting that phospholipid is the binding site for annexin V and that phosphatidylcholine forms at least part of this site. Binding of annexin V did not cause platelet aggregation and did not affect thrombin or collagen induced aggregation. However annexin V significantly inhibited the binding of protein S to the platelet surface.
Department of Medicine, Monash Medical School, Box Hill Hospital, Australia.
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D017304:Annexin A5 / Q000378:metabolism / Q000494:pharmacology*; D001665:Binding Sites; D001667:Binding, Competitive; D001792:Blood Platelets / Q000187:drug effects*; D002118:Calcium / Q000037:antagonists & inhibitors / Q000378:metabolism; D006801:Humans; D008563:Membrane Lipids / Q000378:metabolism; D010446:Peptide Fragments / Q000494:pharmacology; D010713:Phosphatidylcholines / Q000378:metabolism; D010743:Phospholipids / Q000494:pharmacology; D015539:Platelet Activation / Q000187:drug effects; D010974:Platelet Aggregation / Q000187:drug effects; D011485:Protein Binding; D017293:Protein S / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000378:metabolism*; D018000:Receptors, Peptide; D013917:Thrombin / Q000494:pharmacology; D010738:Type C Phospholipases / Q000378:metabolism
D017304:Annexin A5; D008563:Membrane Lipids; D010446:Peptide Fragments; D010713:Phosphatidylcholines; D010743:Phospholipids; D017293:Protein S; D011956:Receptors, Cell Surface; D018000:Receptors, Peptide; C080707:annexin V receptor; D010738:Type C Phospholipases; D013917:Thrombin; D002118:Calcium