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Study on Complexation of Proteins with Polyelectrolytes

蛋白质与聚电解质络合的研究

基本信息

批准号：
05044077
负责人：
KOKUFUTA Etsuo
金额：
$ 2.56万
依托单位：
University of Tsukuba
依托单位国家：
日本
项目类别：
Grant-in-Aid for international Scientific Research
财政年份：
1993
资助国家：
日本
起止时间：
1993 至 1995
项目状态：
已结题

项目摘要

The complexation of proteins with natural and synthetic polyelectrolytes in an aqueous system in interesting from two points of view. The first concerns the way in which the polymers interact with non-flexible protein molecules, an understanding of which could provide a better explanation of the mechanisms of macromolecular interaction available in nature. The second concerns the extent to which biochemical activity is maintained in the resulting complexes, the answer to which is central to the molecular design of composite protein-polymer systems, such as immobilized enzymes, as well as the design of protein separation processes using water-soluble polymers.The present study has dealt with the formation of protein-polyelectrolyte complexes (PPCs) under different conditions of pH and salt concentration. Turbidimetric titration, quasi-elastic light scattering (QELS), static light scattering (SLS), electrophoretic light scattering (ELS) and fluorescence spectroscopy have been employed. I … More n addition, biochemical methods such as the measurement of enzymatic activity have also been employed in the appropriate cases. The main conclusions derived from these previous studies may be summarized as follows : (i) PPCs are formed mainly through electrostatic forces ; (ii) in salt-free systems, at least, protein molecules are complexed with flexible polyelectrolytes through 1 : 1 stoichiometric formation of ion pairs (or salt linkages) between oppositely charged groups ; (iii) the ion pairs between the polyelectrolyte and protein molecules are very weak, some of these bindings severed by changes in pH and the addition of small ions and polyions ; and (iv) there is an appreciable retention of biochemical function in theresultant complexes ; therefore, changes in the three-dimensional conformations of the protein molecules caused by complexation are not so large as to cause a loss of original functions.From the above results the processes of PPC formation may be inferred as follows : At first, many protein molecules are bound to one polyion to form an intrapolymer complex ; especially in salt-free systems, all of its polyion charges are stoichiometrically neutralized by the opposite charges of the proteins. After this, the resultant intrapolymer complexes interact with one another, yielding aggregates or coacervates. It appears likely that such an intrapolymer PPC consists of a number of protein molecules bridged or bundled together by one extended polyelectrolyte ion. The salt linkages maintaining the structure of the intrapolymer PPC seem to be very loose, because changes in pH or additions of other polyions sever some of the salt linkages. This looseness may make it possible for the protein and polyion molecules to undergo stoichiometric neutralization with oppositely charged groups through thermal motion. Less

从两个角度来看，蛋白质与天然和合成聚电解质在水性系统中的络合很有趣。第一个涉及聚合物与非柔性蛋白质分子相互作用的方式，了解这种方式可以更好地解释自然界中大分子相互作用的机制。第二个问题涉及所得复合物中生化活性的维持程度，这个问题的答案对于复合蛋白质-聚合物系统（例如固定化酶）的分子设计以及使用水溶性聚合物的蛋白质分离过程的设计至关重要。本研究涉及在不同pH和盐浓度条件下蛋白质-聚电解质复合物（PPC）的形成。已采用比浊滴定、准弹性光散射（QELS）、静态光散射（SLS）、电泳光散射（ELS）和荧光光谱法。此外，酶活性测量等生化方法也已在适当的情况下使用。从这些先前的研究中得出的主要结论可以总结如下：（i）PPCs主要是通过静电力形成的； (ii) 在无盐系统中，至少，蛋白质分子通过带相反电荷的基团之间以 1:1 化学计量形成离子对（或盐键）与柔性聚电解质复合； (iii)聚电解质和蛋白质分子之间的离子对非常弱，其中一些结合因pH值的变化以及小离子和聚离子的添加而被切断； (iv) 所得复合物明显保留了生化功能；因此，络合引起的蛋白质分子三维构象的变化不会大到导致原有功能的丧失。由上述结果可以推断出PPC形成的过程如下：首先，许多蛋白质分子与一个聚离子结合，形成聚合物内络合物；特别是在无盐系统中，其所有聚离子电荷都被蛋白质的相反电荷按化学计量中和。此后，所得聚合物内复合物彼此相互作用，产生聚集体或凝聚层。这种内聚合物 PPC 很可能由许多通过一种延伸的聚电解质离子桥接或捆绑在一起的蛋白质分子组成。维持聚合物内 PPC 结构的盐键似乎非常松散，因为 pH 值的变化或其他聚离子的添加会切断一些盐键。这种松散性可能使蛋白质和聚离子分子可以通过热运动与带相反电荷的基团进行化学计量中和。较少的