title: Spectroscopic and kinetic studies of the tetraheme flavocytochrome c from Shewanella putrefaciens NCIMB400.
abstract: Electron paramagnetic resonance (EPR) and magnetic circular dichroism (MCD) spectroscopic studies were carried out on the tetraheme flavocytochrome c from Shewanella putrefaciens NCIMB400. The EPR spectrum reveals two sets of g-values--gz = 2.93, gy = 2.28, and gx = 1.51; and gz = 3.58--and the MCD spectrum shows a charge-transfer band at 1510 nm. These data combined show that all four hemes are low spin and have a nitrogenous sixth ligand. Sequence comparisons with other tetraheme cytochromes, particularly that from the purple phototroph H-1-R [Ambler, R.P. (1991) Biochem. Biophys. Acta 1058, 42-47], indicate that the sixth ligands are all histidines. Both the EPR data and the previously reported heme midpoint potentials [-220 and -320 mV; Morris, C.J., Black, A.C., Pealing, S.L., Manson, F.D.C., Chapman, S.K., Reid, G.A., Gibson, D.M., & Ward, F.B. (1994) Biochem. J. 302, 587-593] indicate that the hemes fall into two pairs. Stopped-flow kinetic experiments showed that fumarate-dependent heme oxidation was biphasic (kcat[fast] = 400 +/- 20 s-1; kcat[slow] = 34 +/- 3 s-1), with each phase having the same amplitude, confirming that the hemes are functionally paired.
authors.affiliation: Institute of Cell and Molecular Biology, University of Edinburgh, Scotland, U.K.
authors.forename: S L
authors.initials: SL
authors.lastname: Pealing
authors.forename: M R
authors.initials: MR
authors.lastname: Cheesman
authors.forename: G A
authors.initials: GA
authors.lastname: Reid
authors.forename: A J
authors.initials: AJ
authors.lastname: Thomson
authors.forename: F B
authors.initials: FB
authors.lastname: Ward
authors.forename: S K
authors.initials: SK
authors.lastname: Chapman
mesh_terms: D000595:Amino Acid Sequence; D002942:Circular Dichroism; D003574:Cytochrome c Group / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D006092:Gram-Negative Facultatively Anaerobic Rods / Q000201:enzymology*; D008969:Molecular Sequence Data; D016415:Sequence Alignment; D013385:Succinate Dehydrogenase / Q000737:chemistry*
chemical_list: D003574:Cytochrome c Group; C017165:cytochrome c(3); D013385:Succinate Dehydrogenase