Study on Complexation of Proteins with Polyelectrolytes

从两个角度来看，蛋白质与天然和合成聚电解质在水体系中的络合作用引起了人们的兴趣。第一个涉及聚合物与非柔性蛋白质分子相互作用的方式，了解这一点可以更好地解释自然界中可用的大分子相互作用机制。第二个问题是关于所得到的复合体的生化活性保持到什么程度，这个问题的答案对于蛋白质-聚合物复合体系的分子设计，如固定化酶，以及使用水溶性聚合物的蛋白质分离过程的设计是至关重要的。采用了浊度滴定、准弹性光散射(QELS)、静态光散射(SLS)、电泳光散射(ELS)和荧光光谱等方法。I…此外，在适当的情况下，还采用了生物化学方法，如酶活性的测量。这些研究的主要结论可概括如下：(I)PPC主要是通过静电力形成的；(Ii)在无盐体系中，蛋白质分子至少通过相反电荷基团之间离子对(或盐键)1：1的化学计量形成与柔性聚电解质形成络合；(Iii)聚电解质与蛋白质分子之间的离子对非常弱，其中一些结合被pH的变化以及小离子和聚离子的添加所切断；以及(Iv)在所产生的络合物中有明显的生物化学功能保留；因此，络合引起的蛋白质分子三维构象的变化不会太大而导致原有功能的丧失。从以上结果可以推断PPC的形成过程如下：首先，许多蛋白质分子与一个多离子结合形成聚合物内络合物；特别是在无盐体系中，它的所有多离子电荷都被蛋白质的相反电荷化学计量地中和。在此之后，得到的聚合物内络合物相互作用，产生聚集体或凝聚体。这种聚合物内的PPC很可能是由许多蛋白质分子通过一个延伸的聚电解质离子桥连或捆绑在一起组成的。保持聚合物内PPC结构的盐键似乎非常松散，因为pH的变化或其他多离子的添加切断了一些盐键。这种疏松可能使蛋白质和多离子分子通过热运动与相反带电基团进行化学计量中和。较少

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