MODIFICATION OF PHYSICOCHEMICAL AND BIOPHARMACEUTICAL PROPERTIES OF SUPEROXIDE-DISMUTASE BY CONJUGATION TO THE COPOLYMER OF DIVINYL ETHER AND MALEIC-ANHYDRIDE

The co-polymer of divinyl ether and maleic anhydride (MW 30 000) was c ovalently conjugated to superoxide dismutase in the presence of the pr otecting agent 2,3-dimethylmaleic anhydride as previously reported in this journal (T. Hirano et al., Synthesis of the conjugate of superoxi de dismutase with the copolymer of divinyl ether and maleic anhydride retaining enzymatic activity, J. Control. Release 28 (1994) 203-209). The polymer-enzyme conjugate obtained has been now characterised with respect to its physico-chemical, structural, pharmacokinetic and biolo gical properties. Polymer conjugation was found not to modify the prot ein structure as revealed by circular dichroism measurements but did e nhance the thermal stability of the enzyme. On the other hand, covalen t coupling of the polymer on the protein surface was found to decrease the reversible capability of exchanging the metal co-factor Cu2+ of s uperoxide dismutase. The pharmacokinetic profile of the conjugate afte r intravenous administration in rats indicated that the conjugate pres ented a rapid distribution phase, while the elimination rate was signi ficantly delayed with respect to the native form. Immunoprecipitation studies were performed by using anti-superoxide dismutase serum, which was enriched with polyclonal antibodies. Decreased antigenicity of th e polymer conjugate with respect to the native form was observed.