Cellobiose dehydrogenase: a versatile catalyst for electrochemical applications.

Cellobiose dehydrogenase catalyses the oxidation of aldoses--a simple reaction, a boring enzyme? No, neither for the envisaged bioelectrochemical applications nor mechanistically. The catalytic cycle of this flavocytochrome is complex and modulated by its flexible cytochrome domain, which acts as a built-in redox mediator. This intramolecular electron transfer is modulated by the pH, an adaptation to the environmental conditions encountered or created by the enzyme-producing fungi. The cytochrome domain forms the base from which electrons can jump to large terminal electron acceptors, such as redox proteins, and also enables by that path direct electron transfer from the catalytically active flavodehydrogenase domain to electrode surfaces. The application of electrochemical techniques to the elucidation of the molecular and catalytic properties of cellobiose dehydrogenase is discussed and compared to biochemical methods. The results lead to valuable insights into the function of this cellulose-bound enzyme, but also form the basis of exciting applications in biosensors, biofuel cells and bioelectrocatalysis.