A laser light scattering study of complex formation between soybean peroxidase and poly(N-isopropylacrylamide-co-sodium styrene sulfonate)

The complexation of soybean peroxidase (SBP) with thermosensitive poly(N-isopropylacrylamide-co-sodium styrene sulfonate) (P(iPA-co-SSS)) has studied by laser light scattering. The SBP/P(iPA-co-SSS) complex was found to form at 20 °C in a pH 2.0 solution by way of electrostatic interaction. The effect of temperature, pH, and ionic strength of the solution on the complexation process was investigated in detail. At low ionic strength, a higher temperature brought on stronger hydrophobic association between the copolymer segments and SBP, leading to the formation of compacted complexes with more SBP molecules bound within the P(iPA-co-SSS) chains. The hydrophobic interactions became even more prominent with increasing temperature at high ionic strength, invariably resulting in aggregation of the complexes. In addition, with increasing ionic strength, the number of SBP within the complexes increased first and then decreased due to the charge screening effect. Increasing pH weakened the complexation and resulted in complexes with much smaller number of SBP molecules and a relatively loose structure. These results suggest that both electrostatic and hydrophobic interactions are among the main driving forces for the complexation of P(iPA-co-SSS) with SBP.