Entrapment of glucose oxidase into the cubic Q²³⁰ and Q²²⁴ phases of aqueous monoolein

Abstract

Using X-ray diffraction measurements, the entrapment of glucose oxidase (GOD) from Aspergillus niger was investigated in the reversed bicontinuous cubic phases (Q_II) of aqueous monoolein (MO, 86 wt% monooleoylglycerol). At 25 °C, a partial phase diagram of the MO/GOD/H₂O system indicated that the Q²³⁰ phase can accommodate only up to 0.5 wt% of the commercial GOD preparation. At higher GOD contents, this cubic phase transforms into a reversed hexagonal phase (H_II). On the other hand, the Q²²⁴ phase of MO can accommodate at least up to 6 wt% GOD. The enzyme preparation promotes the thermotropic Q²³⁰ → H_II phase transition, whereas it has no effect on the thermal stability of the Q²²⁴ phase. On the basis of an examination of the calculated geometric parameters of the pseudobinary and pseudoternary cubic phases (thickness of lipid monolayer, diameter of water channels), it is concluded that the native enzyme molecules cannot be located exclusively in the water channels of the phases. The results are also discussed in terms of their possible application in the construction of biosensors.