The heme domain of cellobiose oxidoreductase: a one-electron reducing system.
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.
Mason
Maria G
MG
Department of Biological Sciences, University of Essex, Colchester, UK.
Nicholls
Peter
P
Divne
Christina
C
Hallberg
B Martin
BM
Henriksson
Gunnar
G
Wilson
Michael T
MT
D002237:Carbohydrate Dehydrogenases / Q000737:chemistry / Q000378:metabolism*; D004583:Electrons; D006418:Heme / Q000378:metabolism*; D007700:Kinetics; D010084:Oxidation-Reduction; D020075:Phanerochaete / Q000201:enzymology; D013053:Spectrophotometry
D006418:Heme; D002237:Carbohydrate Dehydrogenases; C019858:cellobiose oxidase