Preparation of Thermo-responsive Polymer Gels Immobilizing Core- Shell Type Bioconjugayes

Immobilization of enzymes is interesting research topic from both fundamental and applied aspects, and various kinds of immobilization methods including chemical and physical procedures have been actively investigated, e.g. the chemical conjugation of enzyme with water-soluble polymers and the physical entrapment into polymer gel matrix (1-5). The advantages of enzyme-immobilization were improvement of storage and operational stabilities. In such studies, the activity of enzyme often decreased after chemical or physical immobilization, although the stabilities were improved. The decrease in enzymatic activity might be induced by the change in environment around enzyme molecule and/or the change in conformation of enzyme molecule through chemical and physical enzymeimmobilization. If the enzyme-immobilization method in consideration of the change in environment and conformation is used, it was expected that it was possible to prevent the decrease in enzyme activity with immobilization. For the chemical conjugation of enzymes and water-soluble polymers concerning limited combinations, which is one of chemical immobilization method, it has been reported that the storage stability of enzyme may improve without a decrease in enzymatic activity. As one of such bioconjugate system, we have recently succeeded the preparation of core-shell type bioconjugates from the mixture of bovine pancreas trypsin and poly(ethylene glycol)-block-poly(α,β-aspartic acid) (PEGPAA) through the crosslinking between trysin and block ionomer by glutaraldehyde (6). The enzymatic activity of trypsin in the core of core-shell type bioconjugates was higher than that of native trypsin, and both the storage stability and operational stability was drastically improved. When core-shell type bioconjugates were physically entrapped in polymer gel matrix by entangled effect, it was expected that the function of enzyme might be maintained even after the entrapment. Because the conformation of trypsin molecules in the bioconjugates was fixed by the glutaraldehyde crosslinking, and the surface of the bioconjugates was surrounded by PEG shell layer. Enzyme molecules in core-shell type bioconjugates were surrounded by polymer chains. Enzyme molecules might not directly interact with the polymer gel matrix, when bioconjugates entrapped in the polymer gels. Consequently, the functions of enzymes might be maintained even after the entrapment in the polymer gels.