Binding of bovine coagulation factor Xa to platelets.
Binding of bovine coagulation factor Xa to platelets.
复制标题
牛凝血因子 Xa 与血小板的结合。
作者：
B. Dahlbäck;J. Stenflo
研究了高纯度的牛凝血因子Xa与洗涤的牛血小板的结合。125 I标记的Xa因子与血小板受体结合，该受体仅在凝血酶或钙离子载体A 23187诱导血小板释放反应后才可接近。酶原因子X不与血小板结合。因子Xa结合是饱和的，可逆的，并与凝血酶形成的速率相关。每个血小板的Xa因子结合位点数为290- 420，表观结合常数估计为2.8 × 109 - 1.0 × 1010 M-1。氟磷酸二异丙酯-因子Xa结合到与因子Xa相同的血小板受体上，表明结合不需要受体蛋白的有限蛋白水解。Xa因子的结合速率很快（2.1 × 10（6）至2.9 × 10（6）M-1 s-1），与多肽激素与其受体的结合速率相似。由二异丙基氟磷酸-Xa因子从血小板受体置换Xa因子有效地阻断凝血酶形成。低浓度的Xa因子在血小板存在下比在磷脂和因子V存在下更有效地催化凝血酶原活化。
The binding of highly purified bovine coagulation factor Xa to washed bovine platelets was studied. 125I-labeled factor Xa underwent binding to a platelet receptor that became accessible only after induction of the platelet release reaction by thrombin or by the calcium ionophore A 23187. The zymogen factor X did not bind to platelets. The factor Xa binding was saturable, reversible, and correlated with the rate of thrombin formation. The number of factor Xa binding sites per platelet was 290--420 and the apparent association constant was estimated to be 2.8 x 109 to 1.0 x 1010 M-1. Diisoprophyl fluorophosphate-factor Xa bound to the same platelet receptor as factor Xa indicating that limited proteolysis of a receptor protein was not required for binding. The rate of factor Xa binding was rapid (2.1 x 10(6) to 2.9 x 10(6) M-1 s-1) and similar to that preveiously found for the rate of binding of polypeptide hormones to their receptors. Displacement of factor Xa from the platelet receptor by diisopropyl fluorophosphate-factor Xa effectively blocked thrombin formation. Low concentrations of factor Xa catalyze prothrombin activation more effectively in the presence of platelets than in the presence of phospholipid and factor V.