Structure and Enzymatic Activity of an Intramolecular Complex of Enzyme with Polyelectrolyte

从两个角度来看，蛋白质与聚电解质的络合是很有趣的。第一个涉及聚合物与非柔性蛋白质分子相互作用的方式。第二个是关于所得到的复合体的生化活性保持的程度，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至关重要。通过结合准弹性光散射(QELS)、静态光散射(SLS)和电泳光散射(ELS)技术，我们认为多离子和蛋白质在低离子强度下会产生一种“聚合物内”复合体。蛋白质与中性聚合物形成的络合物不易发生聚集作用，因此研究了人血清白蛋白(HSA)与聚乙二醇(PEG)的络合作用。不同pH和离子强度(NaCI)的HSA-PEG水溶液的QELS研究表明，HSA-PEG水溶液形成了一种可溶于水的络合物，其大小随聚乙二醇的离子强度和相对分子质量的变化而变化，但不随聚乙二醇和HSA的混合比例的变化而变化。用QELS和荧光光谱研究了1M尿素存在和不存在时的络合作用与pH的关系，结果表明氢键在络合物的形成中起着重要的作用。在pH为2，离子强度为0.1的条件下，SLS和透析法的结合表明，络合生成了几个HSA分子结合到一个聚乙二醇链上的聚合物内络合物。此外，ELS表明，所得到的聚合物内络合物在电泳过程中表现为自由引流线圈。

Complexation of proteins with polyelectrolytes is interesting from two points of view. The first concerns the way in which the polymers interact with non-flexible protein molecules. 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 to the design of protein separation processes using water-soluble polymers.By combinations of quasi-elastic light scattering (QELS), static light scattering (SLS), electrophoretic light scattering (ELS) techniques, we suggested that polyion and protein give forth an "intrapolymer" complex at a low ionic strength. However, such complexes readily aggregate ; therefore, many difficulties arise in the characterization of intrapolymer complex.Complexes of proteins with neutral polymers are less prone to exhibit such aggregation effects ; thus, the complexation between human serum albumin (HSA) and poly(ethylene glycol) (PEG) was studied. QELS study for aqueous HSA-PEG mixtures at different levels of pH and ionic strength (NaCI) showed the formation of a water-soluble complex, the size of which varied depending on both ionic strength and molecular weight of PEG but remained unaltered when the mixing ratio of PEG to HSA was varied. The study of the complexation in the presence and absence of 1M urea as a function of pH by QELS and fluorescence spectroscopy showed that hydrogen bonding plays an important role in the complex formation. A combination of SLS and dialysis method at pH 2 and at ionic-strength of 0.1 demonstrated that the complexation yields an intrapolymer complex in which several HSA molecules bound to a PEG chain. In addition, ELS indicated that the resulting intrapolymer complex behaves like a free draining coil during electrophoresis.