The Search for Ways to Improve the Catalytic Activity of Encapsulated Horseradish Peroxidase

Abstract

Abstract—We consider a previously proposed method for encapsulation of enzymes, which employs the layer-by-layer adsorption of oppositely charged polyelectrolytes onto composite spherulites (calcium carbonate/protein) followed by dissolution of the calcium carbonate support. The goal of this work is to choose conditions for encapsulation of the enzyme horseradish peroxidase by the method so that the catalytic activity of the encapsulated enzyme would be comparable with that of the soluble one. The steps of the fabrication of polyelectrolyte microcapsules with the studied enzyme have been tested. A protocol for obtaining composite spherulites of the desired size ranging from 2 to 10 µm has been developed. It is shown that the catalytic activity of horseradish peroxidase encapsulated in a microcapsule with a positively charged inner surface of the microcapsule envelope (the inner layer modified by polycation polyallylamine hydrochloride) is significantly higher than that of the enzyme encapsulated in a microcapsule with a negatively charged inner layer (modified by polyanion sodium polystyrene sulfonate). At the support dissolution step, ethylene glycol bis-(β-aminoethyl) tetraacetic acid (EGTA), a decalcifying agent used to dissolve CaCO₃ from horseradish peroxidase microcapsules, is significantly less detrimental to enzymes than ethylene diamine tetraacetic acid. The catalytic activity of horseradish peroxidase encapsulated in polyallylamine hydrochloride/sodium polystyrene sulfonate/polyallylamine hydrochloride microcapsules (with positively charged inner surface of the microcapsule envelope) is 60–70% of the activity of the soluble enzyme (in experiments where the calcium-carbonate support of the composite spherulites is dissolved with EGTA).