Biomedical subjects

S Bagby

Publications and source records attributed to S Bagby.

21 records · Page 2Linked to original sources

PubMed1991

Direct electrochemistry of two genetically distinct flavodoxins isolated from Azotobacter chroococcum grown under nitrogen-fixing conditions.

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.

Amino Acid Sequence↗

PubMed1990

Direct electrochemistry of protein-protein complexes involving cytochrome c, cytochrome b5, and plastocyanin.

The direct electrochemistry of the cytochrome c/cytochrome b5 and cytochrome c/plastocyanin complexes has been investigated at edge-plane graphite and modified gold electrode surfaces, which are selective for one of the two components of the complex. Electrochemical response of one protein at an otherwise electrostatically unfavorable electrode surface was achieved in the presence of the other protein, and the calculated heterogeneous electron-transfer rate constant and diffusion coefficient were found to be in good agreement with the values determined previously from the electrochemistry of the individual proteins [Armstrong, F. A., Hill, H. A. O., & Walton, N. J. (1988) Acc. Chem. Res. 21, 407 and references therein]. A dynamic model of the protein-protein-electrode ternary complex is proposed to explain the promotion effect, and this model is supported by a study comparing the electrochemical responses of covalent and electrostatic cytochrome c/plastocyanin complexes. It is also suggested that the behavior of protein-protein complexes at electrode surfaces could be related to that of the complexes associated with biological membranes.

Cytochrome c Group↗

PubMed1990

The complex formed between plastocyanin and cytochrome c. Investigation by NMR spectroscopy.

Spinach plastocyanin and horse heart cytochrome c have been shown, by monitoring the behaviour of the hyperfine-shifted heme resonances of Fe(III) cytochrome c on titration with Cu(II) plastocyanin, to form a 1:1 complex with a dissociation constant of 67 mM (D2O, pH* 7.0, 300 K). The interaction sites on the plastocyanin surface have been investigated in one- and two-dimensional NMR experiments involving competition for plastocyanin between cytochrome c and the paramagnetic cation Cr(NH3)(3+)6. The plastocyanin resonances which are paramagnetically broadened in the spectrum of plastocyanin alone are also broadened in the spectrum of the mixture of the two proteins. This shows that, on the NMR time scale, no plastocyanin residues are hidden from Cr(NH3)(3+)6 by complexation with cytochrome c. [It has been shown that Cr(NH3)(3+)6 does not disrupt formation of the complex between the two proteins.] It appears that initial complexation of cytochrome c takes place at the acidic east site of plastocyanin, and that the extensive negative electrostatic surface of plastocyanin accommodates the paramagnetic probe and cytochrome c simultaneously in a dynamic ternary complex. The location of the electron transfer site on plastocyanin is discussed.

Animals↗