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

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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.