A potentially insect-implantable trehalose electrooxidizing anode

The dominant sugar in the body fluids of many insects is not glucose, the sugar of the vertebrates, but trehalose. In a step toward a cell that would operate in insects, we describe here a trehalose electrooxidizing anode. The novel component of the anode is its engineered, trehalose oxidation catalyzing, FAD-glucose-3-dehydrogenase (G3DH). Screening for gene-sources of G3DH pointed to the G3DH of Agrobacterium tumefaciens. Sequencing of the A. tumefaciens genome revealed a 1.7 kb fragment which contained the G3DH coding gene. The fragment was isolated, cloned and expressed in E. coli strain BL-21, to yield the ∼65 kDa his-tagged flavoenzyme, with a specific activity of ∼2.5 U/mg protein. Electrical wiring of its reaction center to a carbon electrode through a high apparent electron diffusion coefficient (5.8 × 10−6 cm2/s) redox hydrogel with a −0.2 V versus Ag/AgCl redox potential resulted in the trehalose electrooxidizing anode. Trehalose was electrooxidized at pH 7.2 already at −0.36 V versus Ag/AgCl. At 0 V versus Ag/AgCl the trehalose electrooxidation current density was 0.1 mA/cm2.