title: Voltammetry of a flavocytochrome c(3): the lowest potential heme modulates fumarate reduction rates.
abstract: Iron-induced flavocytochrome c(3), Ifc(3), from Shewanella frigidimarina NCIMB400, derivatized with a 2-pyridyl disulfide label, self-assembles on gold electrodes as a functional array whose fumarate reductase activity as viewed by direct electrochemistry is indistinguishable from that of Ifc(3) adsorbed on gold or graphite electrodes. The enhanced stability of the labeled protein's array permits analysis at a rotating electrode and limiting catalytic currents fit well to a Michaelis-Menten description of enzyme kinetics with K(M) = 56 +/- 20 microM, pH 7.5, comparable to that obtained in solution assays. At fumarate concentrations above 145 microM cyclic voltammetry shows the catalytic response to contain two features. The position and width of the lower potential component centered on -290 mV and corresponding to a one-electron wave implicates the oxidation state of the lowest potential heme of Ifc(3) as a defining feature in the mechanism of fumarate reduction at high turnover rates. We propose the operation of dual pathways for electron transfer to the active site of Ifc(3) with the lowest potential heme acting as an electron relay on one of these pathways.
authors.affiliation: Schools, Centre for Metalloprotein Spectroscopy and Biology, University of East Anglia, Norwich NR4 7TJ, United Kingdom. j.butt@uea.ac.uk
authors.forename: J N
authors.initials: JN
authors.lastname: Butt
authors.forename: J
authors.initials: J
authors.lastname: Thornton
authors.forename: D J
authors.initials: DJ
authors.lastname: Richardson
authors.forename: P S
authors.initials: PS
authors.lastname: Dobbin
mesh_terms: D001665:Binding Sites; D003432:Cross-Linking Reagents / Q000737:chemistry; D003574:Cytochrome c Group / Q000737:chemistry*; D004220:Disulfides / Q000737:chemistry; D004563:Electrochemistry; D004579:Electron Transport; D005650:Fumarates / Q000378:metabolism; D006046:Gold; D006420:Hemeproteins / Q000737:chemistry; D007700:Kinetics; D010084:Oxidation-Reduction; D020592:Shewanella / Q000201:enzymology*; D013385:Succinate Dehydrogenase / Q000737:chemistry* / Q000378:metabolism*; D013388:Succinimides / Q000737:chemistry
chemical_list: D003432:Cross-Linking Reagents; D003574:Cytochrome c Group; D004220:Disulfides; D005650:Fumarates; D006420:Hemeproteins; D013388:Succinimides; C018151:N-succinimidyl 3-(2-pyridyldithio)propionate; D006046:Gold; C032005:fumaric acid; C112400:flavocytochrome c3; D013385:Succinate Dehydrogenase