@article {590, title = {Isolation, characterization and gene sequence analysis of a membrane-associated 89 kDa Fe(III) reducing cytochrome c from Geobacter sulfurreducens.}, journal = {Biochem J}, volume = {359}, year = {2001}, month = {2001 Oct 1}, pages = {147-52}, abstract = {Geobacter sulfurreducens is capable of anaerobic respiration with Fe(III) as a terminal electron acceptor via a membrane-bound Fe(III) reductase activity associated with a large molecular mass cytochrome c. This cytochrome was purified by detergent extraction of the membrane fraction, Q-Sepharose ion-exchange chromatography, preparative electrophoresis, and MonoQ ion-exchange chromatography. Spectrophotometric analysis of the purified cytochrome reveals a c-type haem, with no evidence of haem a, haem b or sirohaem. The cytochrome has an M(r) of 89000 as determined by denaturing PAGE, and has an isoelectric point of 5.2 as determined by analytical isoelectric focusing. Dithionite-reduced cytochrome can donate electrons to Fe(III)-nitrilotriacetic acid and synthetic ferrihydrite, thus demonstrating that the cytochrome has redox and thermodynamic properties required for reduction of Fe(III). Analysis using cyclic voltammetry confirmed that the reduced cytochrome can catalytically transfer electrons to ferrihydrite, further demonstrating its ability to be an electron transport mediator in anaerobic Fe(III) respiration. Sequence analysis of a cloned chromosomal DNA fragment revealed a 2307 bp open reading frame (ferA) encoding a 768 amino acid protein corresponding to the 89 kDa cytochrome. The deduced amino acid sequence (FerA) translated from the open reading frame contained 12 putative haem-binding motifs, as well as a hydrophobic N-terminal membrane anchor sequence, a lipid-attachment site and an ATP/GTP-binding site. FerA displayed 20\% or less identity with amino acid sequences of other known cytochromes, although it does share some features with characterized polyhaem cytochromes c.}, keywords = {Amino Acid Sequence, Bacterial Proteins, Chromatography, Ion Exchange, Cloning, Molecular, Cytochrome c Group, Deltaproteobacteria, DNA Primers, Electron Transport, Electrophoresis, Polyacrylamide Gel, Ferric Compounds, Gene Expression Regulation, Bacterial, Molecular Sequence Data, Molecular Weight, Nitrilotriacetic Acid, Oxidation-Reduction, Polymerase Chain Reaction, Sequence Homology, Amino Acid}, issn = {0264-6021}, author = {Magnuson, T S and Isoyama, N and Hodges-Myerson, A L and Davidson, G and Maroney, M J and Geesey, G G and Lovley, D R} } @article {615, title = {The periplasmic 9.6-kilodalton c-type cytochrome of Geobacter sulfurreducens is not an electron shuttle to Fe(III).}, journal = {J Bacteriol}, volume = {181}, year = {1999}, month = {1999 Dec}, pages = {7647-9}, abstract = {Geobacter sulfurreducens contains a 9.6-kDa c-type cytochrome that was previously proposed to serve as an extracellular electron shuttle to insoluble Fe(III) oxides. However, when the cytochrome was added to washed-cell suspensions of G. sulfurreducens it did not enhance Fe(III) oxide reduction, whereas similar concentrations of the known electron shuttle, anthraquinone-2,6-disulfonate, greatly stimulated Fe(III) oxide reduction. Furthermore, analysis of the extracellular c-type cytochromes in cultures of G. sulfurreducens demonstrated that the dominant c-type cytochrome was not the 9.6-kDa cytochrome, but rather a 41-kDa cytochrome. These results and other considerations suggest that the 9.6-kDa cytochrome is not an important extracellular electron shuttle to Fe(III) oxides.}, keywords = {Cytochrome c Group, Electron Transport, Electrophoresis, Polyacrylamide Gel, Ferric Compounds, Gram-Negative Anaerobic Bacteria, Molecular Weight, Periplasm}, issn = {0021-9193}, author = {Lloyd, J R and Blunt-Harris, E L and Lovley, D R} }