title: The heme domain of cellobiose oxidoreductase: a one-electron reducing system.
abstract: Phanerochaete chrysosporium cellobiose oxidoreductase (CBOR) comprises two redox domains, one containing flavin adenine dinucleotide (FAD) and the other protoheme. It reduces both two-electron acceptors, including molecular oxygen, and one-electron acceptors, including transition metal complexes and cytochrome c. If the latter reacts with the flavin, the reduced heme b acts merely as a redox buffer, but if with the b heme, enzyme action involves a true electron transfer chain. Intact CBOR fully reduced with cellobiose, CBOR partially reduced by ascorbate, and isolated ascorbate-reduced heme domain, all transfer electrons at similar rates to cytochrome c. Reduction of cationic one-electron acceptors via the heme group supports an electron transfer chain model. Analogous reactions with natural one-electron acceptors can promote Fenton chemistry, which may explain evolutionary retention of the heme domain and the enzyme's unique character among secreted sugar dehydrogenases.
authors.affiliation: Department of Biological Sciences, University of Essex, Colchester, UK.
authors.forename: Maria G
authors.initials: MG
authors.lastname: Mason
authors.forename: Peter
authors.initials: P
authors.lastname: Nicholls
authors.forename: Christina
authors.initials: C
authors.lastname: Divne
authors.forename: B Martin
authors.initials: BM
authors.lastname: Hallberg
authors.forename: Gunnar
authors.initials: G
authors.lastname: Henriksson
authors.forename: Michael T
authors.initials: MT
authors.lastname: Wilson
mesh_terms: D002237:Carbohydrate Dehydrogenases / Q000737:chemistry / Q000378:metabolism*; D004583:Electrons; D006418:Heme / Q000378:metabolism*; D007700:Kinetics; D010084:Oxidation-Reduction; D020075:Phanerochaete / Q000201:enzymology; D013053:Spectrophotometry
chemical_list: D006418:Heme; D002237:Carbohydrate Dehydrogenases; C019858:cellobiose oxidase