Electron transfer from Phanerochaete chrysosporium cellobiose oxidase to equine cytochrome c and Pseudomonas aeruginosa cytochrome c-551.
The electron-transfer reactions of cellobiose oxidase (CBO) have been investigated by conventional and by rapid-scan stopped-flow spectroscopy at pH 6.0. Analysis of the absorbance/time/wavelength matrix by Singular Value Decomposition (SVD) confirms earlier studies showing that cellobiose rapidly reduces the flavin group (7.7 s-1; cellobiose, 100 microM) which in turn slowly (0.2 s-1) reduces the cytochrome b moiety. In the presence of CBO, cellobiose reduces cytochromes c in a reaction that does not depend on oxygen or superoxide. The rate limit for this process is independent of the source of the cytochromes c and is identical with the rate of cytochrome b reduction. Rapid-mixing experiments show that cytochrome b may donate electrons very rapidly to either mammalian cytochrome c or bacterial cytochrome c-551. The reactions were second-order (kc = 1.75 x 10(7) M-1 x s-1; kc-551 = 4.3 x 10(6) M-1 x s-1; pH 6.0, 21 degrees C and I0.064) and strongly ionic-strength (I)-dependent: kc decreasing with I and kc-551 increasing with I. These results suggest the electron-transfer site near cytochrome b bears a significant negative charge. Equilibrium gel chromatography confirms that CBO oxidase and positively charged mammalian cytochrome c make stable complexes. These results are discussed in terms of a model suggesting an electron-transfer role for cytochrome b in vivo, possibly connected with radical-mediated cellulose breakdown.
Rogers
M S
MS
Department of Chemistry and Biolgical Chemistry, University of Essex, Wivenhoe Park, Colchester, U.K.
Jones
G D
GD
Antonini
G
G
Wilson
M T
MT
Brunori
M
M
D000818:Animals; D001426:Bacterial Proteins; D001487:Basidiomycota / Q000201:enzymology*; D002237:Carbohydrate Dehydrogenases / Q000378:metabolism*; D002850:Chromatography, Gel; D003574:Cytochrome c Group / Q000378:metabolism*; D004579:Electron Transport; D006736:Horses; D007700:Kinetics; D010084:Oxidation-Reduction; D011550:Pseudomonas aeruginosa / Q000201:enzymology*
D001426:Bacterial Proteins; D003574:Cytochrome c Group; C017167:cytochrome C(551); D002237:Carbohydrate Dehydrogenases; C019858:cellobiose oxidase