Molecular Basis for Directional Electron Transfer

Biological macromolecules involved in electron transfer reactions display chains of closely packed redox cofactors when long distances must be bridged. This is a consequence of the need to maintain a rate of transfer compatible with metabolic activity in the framework of the exponential decay of ele...

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Bibliographic Details
Published in:The Journal of biological chemistry 2010-04, Vol.285 (14), p.10370-10375
Main Authors: Paquete, Catarina M., Saraiva, Ivo H., Calçada, Eduardo, Louro, Ricardo O.
Format: Article
Language:English
Subjects:
Bioenergetics/Electron Transport
Cytochrome c Group - chemistry
Cytochrome c Group - metabolism
Cytochromes/Cytochrome c
Electron Transfer
Electron Transport
Electrons
Enzymes/Cooperativity
Enzymes/Heme
Enzymology
Heme - chemistry
Heme - metabolism
Kinetics
Metal Respiration
Models, Molecular
Oxidation-Reduction
Shewanella - metabolism
Shewanella frigidimarina
Shewanella oneidensis
Thermodynamics
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Summary:Biological macromolecules involved in electron transfer reactions display chains of closely packed redox cofactors when long distances must be bridged. This is a consequence of the need to maintain a rate of transfer compatible with metabolic activity in the framework of the exponential decay of electron tunneling with distance. In this work intermolecular electron transfer was studied in kinetic experiments performed with the small tetraheme cytochrome from Shewanella oneidensis MR-1 and from Shewanella frigidimarina NCIMB400 using non-physiological redox partners. This choice allowed the effect of specific recognition and docking to be eliminated from the measured rates. The results were analyzed with a kinetic model that uses the extensive thermodynamic characterization of these proteins reported in the literature to discriminate the kinetic contribution of each heme to the overall rate of electron transfer. This analysis shows that, in this redox chain that spans 23 Å, the kinetic properties of the individual hemes establish a functional specificity for each redox center. This functional specificity combined with the thermodynamic properties of these soluble proteins ensures directional electron flow within the cytochrome even outside of the context of a functioning respiratory chain.
ISSN:0021-9258
1083-351X
DOI:10.1074/jbc.M109.078337