中文摘要：

尖吻蝮蛇毒抗凝血因子I（ACFI）是活化凝血因子X（FXa）结合蛋白，具有显著的抗凝血活性．用荧光光谱研究了Sr^＋诱导ACF I的结构稳定性及重新折叠．结果表明，脱钙ACF I（apo-ACFI）可结合两个Sr^＋．ACF I与FXa的结合反应不是绝对依赖于Ca^2＋，Sr^2＋也可以诱导ACF I与FXa的结合反应．盐酸胍诱导的Sr^2＋重组ACFI（Sr^2＋-ACF I）去折叠过程是一个三态过程，有一个稳定的中间态．像Ca^2＋一样，Sr^2＋不仅能显著增加ACF I的结构稳定性，而且在不改变变性剂浓度条件下，能诱导去折叠的脱钙ACF I重新折叠成Sr^2＋-ACF I的中间态．Sr^2＋诱导apo-ACF I重新折叠过程包含快慢两步反应，Sr^2＋取代Ca^2＋只降低快折叠反应速度，而不影响慢折叠反应速度．这说明，金属离子影响快折叠过程，而慢折叠过程只决定于蛋白质本身性质．

英文摘要：

Anticoagulation factor I （ACF I） isolated from the venom of Agkistrodon acutus is an activated coagulation factor X （FXa）-binding protein with marked anticoagulant activity. Sr^2＋ induced stabilization and rdolding of ACF I have been studied by fluorescence. Here, we show that Ca^2＋-free ACF I （apo-ACF I） can bind with two Sr^2＋ ions. The binding of ACF I to FXa does not have an absolute requirement for Ca^2＋ ions, and Sr^2＋ ions can also induce the binding of ACF I to FXa. The GdnHCl-induced unfolding of Sr^2＋-reconstituted ACF I （Sr^2＋ ACF I） is a three state transition with an intermediate state. Like Ca^2＋ , Sr^2＋ not only significantly increases the structural stability of ACF I against GdnHCl, but also induces the refolding of the unfolded apo ACF I merely by adding 1 mM Sr^2＋ to the unfolded apo-ACF I without changing the concentration of the denaturant. The kinetic results of Sr^2＋-induced refolding provide evidences that Sr^2＋-ACF I consists of two refolding phases and that the substitution of Sr^2＋ for Ca^2＋ in ACF I only affects the rate for the faster refolding phase and does not affect the rate for the slower refolding phase, suggesting that the faster refolding step is affected by the binding-metal ion while the slower refolding step only depends on the intrinsic character of the protein.