Formation of an intrapolymer complex from human serum albumin and poly(ethylene glycol)

Complexation between human serum albumin (HSA) and poly(ethylene glycol) (P EG) was studied using different experimental techniques: quasi-elastic ligh t scattering (QELS), static light scattering (SLS), electrophoretic light s cattering (ELS), dialysis, and fluorescence spectroscopy. The QELS study fo r aqueous HSA-PEG mixtures at different levels of pH and ionic strength (Na Cl) showed the formation of a water-soluble complex, the size of which vari ed depending on both the ionic strength and the molecular weight of PEG but remained unaltered when the mixing ratio of PEG to HSA was varied. The stu dy of the complexation in the presence and absence of 1 M urea as a functio n of pH by QELS and fluorescence spectroscopy strongly suggested that hydro gen bonding plays an important role in the complex formation. A combination of SLS and dialysis at pH 2 and at the ionic strength 0.1 demonstrated tha t the complexation yielded an "intrapolymer" complex in which several HSA m olecules bound to a PEG chain. In addition, ELS indicated that the resultin g intrapolymer complex behaves like a free draining coil during electrophor esis.