Binding energetics of lysozyme to copolymers of N-isopropylacrylamide with sodium sulfonated styrene.

Interpolyelectrolyte complexes of lysozyme with thermosensitive N-isopropylacrylamide-sodium sulfonated styrene copolymers of different charge density were investigated by high-sensitivity differential scanning calorimetry (HS-DSC) at pH 4.6-7.2 and low ionic strength. A general property of the complexes for all copolymers investigated was a decrease in the conformational stability of the bound protein. This suggested the preferential binding of the unfolded protein to the polymer matrix. The isotherms of lysozyme binding to the copolymers were derived from the HS-DSC data. They indicate that the binding is irreversible and charge stoichiometric.