title: Characterization of the paramagnetic iron-containing redox centres of Thiosphaera pantotropha periplasmic nitrate reductase.
abstract: Electron paramagnetic resonance spectroscopy signals attributable to low-spin haem c in the oxidised protein and [4Fe-4S]1+ in the dithionite-reduced protein were identified, at low temperature, in Thiosphaera pantotropha periplasmic nitrate reductase. Spin integration of these signals as well as elemental analysis suggest a stoichiometry of 1.3-1.6 c-haem and 1 [4Fe-4S] cluster per enzyme molecule. The Em (at pH 7.4) of the [4Fe-4S]2+,1+ couple, -160 mV, means that it is unlikely to be physiologically reducible. Peptide sequences from the 90 kDa subunit indicate that the enzyme is a member of the family of molybdopterin guanine dinucleotide-binding polypeptides, the majority of which possess a putative [4Fe-4S] cluster binding sequence and thus may also bind a (low potential) iron-sulphur cluster.
authors.affiliation: Centre for Metalloprotein Spectroscopy and Biology, School of Biological Sciences, University of East Anglia, Norwich, UK.
authors.forename: J
authors.initials: J
authors.lastname: Breton
authors.forename: B C
authors.initials: BC
authors.lastname: Berks
authors.forename: A
authors.initials: A
authors.lastname: Reilly
authors.forename: A J
authors.initials: AJ
authors.lastname: Thomson
authors.forename: S J
authors.initials: SJ
authors.lastname: Ferguson
authors.forename: D J
authors.initials: DJ
authors.lastname: Richardson
mesh_terms: D000595:Amino Acid Sequence; D001420:Bacteria, Aerobic / Q000201:enzymology*; D002462:Cell Membrane / Q000201:enzymology*; D004578:Electron Spin Resonance Spectroscopy; D006150:Guanine Nucleotides; D006418:Heme / Q000031:analogs & derivatives / Q000737:chemistry; D007506:Iron-Sulfur Proteins / Q000737:chemistry*; D008969:Molecular Sequence Data; D050901:Nitrate Reductase; D009565:Nitrate Reductases / Q000737:chemistry* / Q000145:classification; D010084:Oxidation-Reduction; D010446:Peptide Fragments; D011622:Pterins; D017421:Sequence Analysis; D017386:Sequence Homology, Amino Acid
chemical_list: D006150:Guanine Nucleotides; D007506:Iron-Sulfur Proteins; D010446:Peptide Fragments; D011622:Pterins; C063761:molybdopterin guanine dinucleotide; C031690:heme C; D006418:Heme; D009565:Nitrate Reductases; D050901:Nitrate Reductase