Activation of the zymogen, factor X, by either the intrinsic or extrinsic factor Xase complexes produces the active serine protease factor Xa (1,2). The activation of factor X requires proteolytic cleavage of the heavy chain, resulting in the release of an activation glycopeptide. The heavy chain region in factor Xa contains the serine protease catalytic domain, while the light chain, as in the zymogen, contains the membrane binding domain.
Factor Xa (molecular weight 46,000) participates in the prothrombinase complex, which catalyzes the rapid conversion of prothrombin to thrombin. Prothrombinase is an enzyme complex composed of factor Xa (enzyme) and factor Va (cofactor) assembled on a cellular surface in the presence of calcium ions. Although factor Xa can independently catalyze the activation of prothrombin, the rate at which this reaction occurs is increased nearly 300,000-fold with complete assembly of the prothrombinase complex. The clotting activity of factor Xa in vivo is terminated by either inactivation of the cofactor, factor Va, or by direct inhibition of factor Xa by inhibitors, such as ATIII, after disassembly of the prothrombinase complex.
In addition to its broad application in coagulation research, factor Xa can be utilized for site specific cleavage of fusion proteins expressed in bacteria (9-12). A factor Xa-sensitive site is incorporated between the recombinant protein of interest and peptides or proteins which facilitate purification and/or expression. The target protein is released from the expressed hybrid by cleavage with factor Xa. The factor Xa can then be easily removed by affinity chromatography.
Factor Xa is prepared by activating purified factor X with the factor X activator isolated from Russell"s viper venom. Factor Xa is purified from the activation mixture by chromatography over benzamidine-Sepharose followed by gel filtration (1,3). Several modified forms of factor Xa are also available including: A) active-site blocked factor Xa containing either the tripeptide chloromethyl ketone inhibitor EGRck, or the fluorescent inhibitor Dansyl-EGRck; and B) human Gla-domainless β-factor Xa. The enzyme is supplied in 50% (vol/vol) glycerol/H2O and should be stored at -20°C. Purity is determined by SDS-PAGE analysis and activity is measured in a factor Xa clotting assay and/or chromogenic substrate assay. Lot to lot consistency ensures reproducible results every time.
Cell culture: For experiments involving cell cultures, please contact us to discuss custom, low endotoxin lots designated for cell culture use.
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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。
