Catalase-conjugated liposomes encapsulating glucose oxidase for controlled oxidation of glucose with decomposition of hydrogen peroxide produced

The catalase-conjugated liposome encapsulating glucose oxidase (CLG) was prepared for developing a novel liposomal system for glucose oxidation with controllable enzyme activities. The catalase molecules were conjugated to the surface of liposome with 100 nm in mean diameter through coupling with the membrane-incorporated 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-(glutaryl) (NGPE) at its mole fraction fG of 0.05 or 0.15. The average number of enzyme molecules per CLG with fG of 0.15 was 8.7 for glucose oxidase and 6.5 for catalase. The CLG-catalyzed oxidation of glucose was performed at 40 °C for prolonged period up to 99 h. The CLG with fG of 0.15 gave larger oxidation rate than that with fG of 0.05. In the fed-batch oxidation of glucose catalyzed by the former CLG, the stable oxidation rate was observed for 75 h with negligible accumulation of H2O2 produced because of the durable catalytic actions of the liposomal enzymes. The oxidation rate of the CLG reaction increased to 1.1 mM-glucose/(h mM-lipid) at the acidic pH in the internal phase of liposome and the neutral pH in the external one corresponding to the optimal pH conditions for the activities of glucose oxidase and catalase, respectively. The oxidation rate catalyzed by the CLG could be controlled by adding sublytic concentrations of cholate to increase permeability of the liposome membrane to glucose. The catalase-conjugated liposomal system is potentially utilized for controlling the rate of reactions catalyzed by a variety of oxidases.