Plasminogen is a single chain glycoprotein zymogen which is synthesized in the liver and circulates in plasma at a concentration of approximately 2.4 µM (1,2). The plasminogen molecule contains 790 amino acids, 24 disulfide bridges, no free sulfhydryls and 5 regions of internal sequence homology, known as kringles, between Lys77 and Arg560. These five triple-looped, three disulfide bridged, kringle regions are homologous to the kringle domains in t-PA, u-PA and prothrombin. Plasminogen contains one high affinity (Kd=9x10-6M) and four low affinity (Kd=5x10-3M) lysine binding sites. The high affinity binding site resides within the first kringle region of plasminogen. The interaction of plasminogen with fibrin and α2-antiplasmin is mediated by these lysine binding sites. Native glu-plasminogen (Mr=88,000) is readily converted to Lys-77-plasminogen (Mr=83,000) by plasmin hydrolysis of the Lys76-Lys77 peptide bond. Elastase catalyzed cleavage of the Val441-Val442 peptide bond of glu-plasminogen yields a functionally active zymogen termed Val-442 plasminogen or mini-plasminogen.
The conversion of plasminogen to plasmin occurs by a variety of mechanisms, but all result in hydrolysis of the Arg560-Val561 peptide bond of plasminogen, yielding two chains which remain covalently associated by a disulfide bond.
Native glu-plasminogen is prepared from fresh frozen human plasma by a modification of the procedure of Castellino (3), utilizing gel filtration and affinity chromatography. The two carbohydrate variants of glu-plasminogen (CHOI and CHOII) are isolated by gradient elution from lysine-Sepharose using the lysine analog, e-aminocaproic acid (3). The plasminogen is supplied in 50% (vol/vol) glycerol/H2O for storage at -20oC. Purity is determined by SDS-PAGE analysis.
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根据磷酸化的底物不同，可将蛋白激酶分为组蛋白蛋白激酶、酪蛋白蛋白激酶等，但由于蛋白激酶可磷酸化底物的多样化，这种分法很不确切，已经被根据底物磷酸化氨基酸的分类方法所取代，有些如酪蛋白蛋白激酶，只是由于习惯而一直被沿用下来。根据有无调节物将蛋白激酶分为信使依赖的蛋白激酶和非信使依赖的蛋白激酶，有些信使依赖的蛋白激酶的首字母缩略词已为人们所接受，如cAMP依赖的蛋白激酶PKA、钙和磷脂依赖的蛋白激酶PKC以及钙依赖钙调素不依赖的蛋白激酶CDPK等，它们彼此间存在结构和功能上的相关关系。
也有人认为：蛋白激酶在信号转导中主要作用有两个方面：其一是通过磷酸化调节蛋白质的活性,磷酸化和去磷酸化是绝大多数信号通路组分可逆激活的共同机制,有些蛋白质在磷酸化后具有活性,有些则在去磷酸化后具有活性；其二是通过蛋白质的逐级磷酸化,使信号逐级放大,引起细胞反应.
根据PTK是否存在于细胞膜受体可将其分成受体型和非受体型。向左转|向右转
protease
水解蛋白质肽键的一类酶的总称。按其水解多肽的方式，可以将其分为内肽酶和外肽酶两类。内肽酶将蛋白质分子内部切断，形成分子量较小的月示和胨。外肽酶从蛋白质分子的游离氨基或羧基的末端逐个将肽键水解，而游离出氨基酸，前者为氨基肽酶后者为羧基肽酶。按其活性中心和最适pH值，又可将蛋白酶分为丝氨酸蛋白酶、巯基蛋白酶、金属蛋白酶和酸性蛋白酶。按其反应的最适pH值，分为酸性蛋白酶、中性蛋白酶和碱性蛋白酶。工业生产上应用的蛋白酶，主要是内肽酶。
蛋白激酶
protein kinase
又称蛋白质磷酸化酶(protein phosphakinase)。一类催化蛋白质磷酸化反应的酶。
大家好，有几个设计的药物分子需要测试活性，不知道谁能提供下能做相关测试服务的机构或个人信息不?非常感谢！
