Mechanism for High Stability of Liposomal Glucose Oxidase to Inhibitor Hydrogen Peroxide Produced in Prolonged Glucose Oxidation

Glucose oxidase (GO) was encapsulated in the liposomes composed of POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) to increase the enzyme stability through its decreased inhibition because of hydrogen peroxide (H2O2) produced in the glucose oxidation. The GO-containing liposomes (GOLs) were completely free of the inhibition even in the complete conversion of 10 mM glucose at 25 °C because the H2O2 concentration was kept negligibly low both outside and inside liposomes throughout the reaction. It was interestingly revealed that the H2O2 produced was decomposed not only by a slight amount of catalase originally contained in the commercially available GO but also by the lipid membranes of GOL. As compared to the GOL-catalyzed reaction, the free GO-catalyzed reaction more highly accumulated H2O2 because of the more rapid glucose conversion despite containing free catalase, leading to the completely inhibited GO before reaching a sufficient glucose conversion. This suggested that only the liposomal catalase could continue to catalyze the H2O2 decomposition. The effect of the glucose oxidation rate, i.e., the H2O2 production rate on the liposomal GO inhibition, was also examined employing the various GOLs with different permeabilities to glucose present in their external phase. It was concluded that the liposomal GO free of the inhibition could be obtained when the GOL-catalyzed H2O2 formation rate was limited by such a suitable lipid bilayer as POPC membrane so that the rate was well-balanced with the sum of the above two H2O2 decomposition rates. The highly stable GOL obtained in the present paper was shown to be a useful biocatalyst for the prolonged glucose oxidation.