Interpolyelectrolyte complexes of soybean peroxidase with thermoresponsive copolymers

Interpolyelectrolyte complexes of soybean peroxidase with thermoresponsive N-isopropylacrylamide-sodium styrenesulfonate copolymers of various compositions are studied by the methods of high-sensitivity differential scanning calorimetry, velocity sedimentation, and nephelometry. It is shown that the enzyme preserves its tertiary structure in complexes, although the conformational stability of bound protein is lower than that of free protein. Complexes of any compositions, including stoichiometric complexes, are soluble at room temperature but precipitate during heating in the region of the conformational transition of the copolymer accompanied by formation of the complex gel. Isotherms of enzyme binding by complex gels are constructed, and their analysis makes it possible to reveal two types of binding in the system: a relatively strong stoichiometric binding of the enzyme with the copolymers and a weaker binding of the protein in the coacervate phase of the complex gel. A high yield of the protein in the complex gel, reversibility of binding, and preservation of the tertiary structure of the enzyme in complexes with the copolymers make protein-thermoresponsive polyelectrolyte systems promising for bioseparation.