Liposomes incorporating hydrophobically modified glucose oxidase

Glucose oxidase (GOD) was hydrophobically modified by conjugating palmitic acids to the amino groups of the enzyme. The number of palmitic acid residues conjugated to GOD was determined by using trinitrobenzenesulfonic acid (TNBS). According to the result, six palmitic acids turned out to be covalently attached to one GOD molecule. The activity of the modified GOD was 75%–80% of that of the native one, and due to the conjugated alkyl chain, the modified GOD was more surface-active than the native one. The modified GOD was incorporated into the liposomal bilayer of dioleoylphosphatidylethanolamine (DOPE) and cholesteryl hemisuccinate (CHEMS) by a detergent removal method. According to the results of the pH-dependent release, no significant release was observed in 60 sec at pH 8.2. An appreciable amount of calcein released at pH 7.0. A marked amount released at pH 6.0. The degree of release became more extensive at pH 5.0 and pH 5.6. This is possibly because the liposome is disintegrated into hexagonal phases under acidic conditions.