Gilbert G E, Arena A A
Department of Medicine, Brockton-West Roxbury Veterans Administration Medical Center, MA 02132, USA.
J Biol Chem. 1995 Aug 4;270(31):18500-5. doi: 10.1074/jbc.270.31.18500.
Synthetic membranes of phosphatidylcholine require inclusion of at least 5% phosphatidylserine (Ptd-L-Ser) to form binding sites for factor VIII. The relatively high requirement for Ptd-L-Ser suggests that stimulated platelets may contain another membrane constituent that enhances expression of factor VIII-binding sites. We report that phosphatidylethanolamine (PE), which is exposed in concert with Ptd-L-Ser in the course of platelet stimulation, induces high affinity binding sites for factor VIII on synthetic membranes containing 1-15% Ptd-L-Ser. The affinity of factor VIII for binding sites on membranes of Ptd-L-Ser/PE/phosphatidylcholine in a 4:20:76 ratio was 10.2 +/- 3.5 nM with 180 +/- 33 phospholipid molecules/site. PE did not induce binding sites on membranes of 4% Ptd-D-Ser, indicating that the induced binding sites require the correct stereochemistry of Ptd-L-Ser as well as PE. Egg PE and dimyristoyl-PE were equivalent for inducing factor VIII-binding sites, indicating that hexagonal phase-inducing properties of PE are not important. We conclude that PE induces high affinity factor VIII-binding sites on membranes with physiologic mole fractions of Ptd-L-Ser, possibly including those of stimulated platelets.
磷脂酰胆碱合成膜需要包含至少5%的磷脂酰丝氨酸（Ptd-L-Ser）才能形成因子VIII的结合位点。对Ptd-L-Ser的相对高需求表明，受刺激的血小板可能含有另一种膜成分，可增强因子VIII结合位点的表达。我们报告，在血小板刺激过程中与Ptd-L-Ser协同暴露的磷脂酰乙醇胺（PE），在含有1-15% Ptd-L-Ser的合成膜上诱导出因子VIII的高亲和力结合位点。因子VIII对Ptd-L-Ser/PE/磷脂酰胆碱比例为4:20:76的膜上结合位点的亲和力为10.2±3.5 nM，每个位点有180±33个磷脂分子。PE在4% Ptd-D-Ser的膜上不诱导结合位点，表明诱导的结合位点需要Ptd-L-Ser的正确立体化学结构以及PE。鸡蛋PE和二肉豆蔻酰-PE在诱导因子VIII结合位点方面等效，表明PE的六方相诱导特性并不重要。我们得出结论，PE在具有生理摩尔分数的Ptd-L-Ser的膜上诱导出高亲和力的因子VIII结合位点，可能包括受刺激血小板的膜。
