title: Direct electrochemistry of two genetically distinct flavodoxins isolated from Azotobacter chroococcum grown under nitrogen-fixing conditions.
abstract: Two genetically distinct flavodoxins, designated AcFldA and AcFldB, were isolated from Azotobacter chroococcum (MCD1155) grown under nitrogen-fixing conditions. AcFldA and AcFldB differ in their midpoint potentials for the semiquinone-hydroquinone couple (Em -305 mV and -520 mV respectively). Only AcFldB was competent to act as an electron donor to the Mo-containing nitrogenase of A. chroococcum. The N-terminal amino acid sequence (20 residues) of AcFldB was identical with that predicted from the nifF DNA sequence of A. vinelandii OP [Bennett, Jacobsen & Dean (1988) J. Biol. Chem. 263, 1364-1369], suggesting that AcFldB is the nifF gene product of A. chroococcum (MCD1155). Direct fast reversible electrochemistry of these flavodoxins has been achieved at a polished edge-plane graphite electrode using the aminoglycoside neomycin as a promoter. The heterogeneous rates of electron transfer between the graphite electrode and AcFldA and AcFldB were determined to be 1.2 x 10(-3) cm.s-1 and 2.0 x 10(-3) cm.s-1 respectively. The natures of two minor species of flavodoxin designated AcFldC and AcFldD, which were resolved by f.p.l.c., are also discussed.
authors.affiliation: Inorganic Chemistry Laboratory, University of Oxford, U.K.
authors.forename: S
authors.initials: S
authors.lastname: Bagby
authors.forename: P D
authors.initials: PD
authors.lastname: Barker
authors.forename: H A
authors.initials: HA
authors.lastname: Hill
authors.forename: G S
authors.initials: GS
authors.lastname: Sanghera
authors.forename: B
authors.initials: B
authors.lastname: Dunbar
authors.forename: G A
authors.initials: GA
authors.lastname: Ashby
authors.forename: R R
authors.initials: RR
authors.lastname: Eady
authors.forename: R N
authors.initials: RN
authors.lastname: Thorneley
mesh_terms: D000595:Amino Acid Sequence; D001395:Azotobacter / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D004269:DNA, Bacterial / Q000235:genetics; D004563:Electrochemistry; D005418:Flavodoxin / Q000737:chemistry / Q000235:genetics* / Q000302:isolation & purification; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D009586:Nitrogen Fixation / Q000235:genetics*; D010449:Peptide Mapping; D013053:Spectrophotometry
chemical_list: D004269:DNA, Bacterial; D005418:Flavodoxin