Fig. 1.

Catalytic cycle of GDHs. The enzyme in the oxidized resting state accepts electrons from a reducing sugar, like D-glucose, which is oxidized at the C1 position and converted into D-glucono-δ-lactone; this causes the protein solution to turn from yellow to colorless, due to the reduction of the FAD cofactor. In the second half-reaction electrons are transferred from reduced FADH₂ to aromatic electron acceptors, such as quinones. The enzymatic product D-glucono-δ-lactone undergoes spontaneous hydrolysis in water