Prothrombin is a vitamin K-dependent plasma protein which is synthesized in the liver (1). Prior to secretion into plasma, prothrombin undergoes post-translational modification by a vitamin K-dependent carboxylase which converts ten specific glutamic acid residues to γ-carboxyglutamic acid (gla). The ten gla residues are located within the first 40 amino acids of the mature protein and contribute to the ability of prothrombin to bind to negatively charged phospholipid membranes. Prothrombin contains two regions of internal homology which are referred to as "kringle" structures. These regions of conspicuous secondary structure are located between residues 40 and 270 of the mature plasma protein and replace the growth factor domains found in several other plasma serine proteases. Thus far, no function has been ascribed to these regions, but there is suspicion that they may play a role in one of several binary protein interactions involving prothrombin. The mature single chain protein circulates in plasma as a zymogen and, during coagulation, is proteolytically activated to the potent serine protease α-thrombin. This proteolysis is catalyzed by the prothrombinase enzyme complex. During activation, prothrombin is cleaved at Arg271-Thr272 (human) / Arg273-Thr274 (bovine) and at Arg320-Ser321 (human) / Arg323-Ser324 (bovine) to a "pro" fragment (fragment 1.2) and thrombin, the latter of which is composed of two chains covalently linked by a disulfide bond. In the case of human prothrombin/thrombin, there is an additional thrombin feed-back cleavage at Arg284-Thr285 resulting in an additional 13 amino acids being removed from the mature thrombin “A” chain.
Human prothrombin is prepared from fresh frozen human plasma as described by Bajaj and coworkers (2). Bovine prothrombin is prepared from fresh bovine plasma using a modification of the procedure described by Owen and coworkers (3). Purified prothrombin is supplied in 50% (vol/vol) glycerol/H2O and should be stored at -20oC. Purity is determined by SDS-PAGE analysis, and activity is measured by clotting and/or chromogenic substrate assay, following conversion of prothrombin to thrombin.
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谢谢各位
非常急！
①在用超滤除白蛋白，IgG中硫酸铵盐时，膜包该如何选择？选择几个？
②如用凝胶过滤来分级纯化血清中65%硫酸铵盐析出的白蛋白和纯化33%硫酸铵盐析出的IgG，其填充介质应选择什么？其洗脱缓冲液应用什么好？
下面有些关于这方面的数据，供参考：
①牛血清白蛋白：分子量：66210；分子形状：椭圆形；分子大小：
40Å*140Å；等电点：4.7；血浆中的含量：52.0g/L。
②IgG:分子量：15300；分子形状：球状；等电点：5.8—7.3;血浆中含量：2.0g/L。
③另外，我从书上看到说：凝胶过滤在分级方法中分辨率为中等，但对脱盐效果优良；流速较低，对分级每周期约≥8小时，对脱盐仅30分钟；适用于大规模纯化的最后步骤，在纯化过程的任何阶段均可进行脱盐处理，尤其适用于两种缓冲液交替时。
期待您的帮助，谢谢您。
（一）高密度脂蛋白胆固醇（HDL-C）
【参考值】
0.94～2.0mmol/L
【临床意义】
降低具有临床意义。HDL-C与TG呈负相关系，见于冠心病、动脉粥样硬化、糖尿病、肝脏损害、肾病综合征。
（二）低密度脂蛋白胆固醇（LDL-C）
【参考值】
沉淀法:2.07～3.12mmol/L，3.15～3.61mmol/L为边缘升高，≥3.64mmol/L为升高。
【临床意义】
升高具有临床意义。LDL-C升高与冠心病发病呈正相关系。
（三）脂蛋白（a），LP（a）
【参考值】 <300mg/L
【临床意义】
脂蛋白（a）升高已作为冠心病及脑血管疾病发病的独立危险因素。
