scholarly journals Electrochemical and spectroscopic characterization of the 7Fe form of ferredoxin III from Desulfovibrio africanus

1989 ◽  
Vol 264 (1) ◽  
pp. 265-273 ◽  
Author(s):  
F A Armstrong ◽  
S J George ◽  
R Cammack ◽  
E C Hatchikian ◽  
A J Thomson
Keyword(s):  
Low Temperature ◽  
Pyrolytic Graphite ◽  
Spectroscopic Characterization ◽  
Carbon Electrode ◽  
Standard Hydrogen Electrode ◽  
Hydrogen Electrode ◽  
Iron Cluster ◽  
Desulfovibrio Gigas ◽  
Acid Labile

Desulfovibrio africanus ferredoxin III is a monomeric protein (Mr 6585) containing seven cysteine residues and 7-8 iron atoms and 6-8 atoms of acid-labile sulphur. It is shown that reversible unmediated electrochemistry of the two iron-sulphur clusters can be obtained by using a pyrolytic-graphite-‘edge’ carbon electrode in the presence of an appropriate aminoglycoside, neomycin or tobramycin, as promoter. Cyclic voltammetry reveals two well-defined reversible waves with E0′ = -140 +/- 10 mV and -410 +/- 5 mV (standard hydrogen electrode) at 2 degrees C. Bulk reduction confirms that each of these corresponds to a one-electron process. Low-temperature e.p.r. and magnetic-c.d. spectroscopy identify the higher-potential redox couple with a cluster of core [3Fe-4S]1+.0 and the lower with a [4Fe-4S]2+.1+ centre. The low-temperature magnetic-c.d. spectra and magnetization properties of the three-iron cluster show that it is essentially identical with that in Desulfovibrio gigas ferredoxin II. We assign cysteine-11, -17 and -51 as ligands of the [3Fe-4S] core and cysteine-21, -41, -44 and -47 to the [4Fe-4S] centre.

Low-temperature and time-resolved spectroscopic characterization of the LOV2 domain of Avena sativa phototropin 1

2004 ◽  
Author(s):  
Magdalena Gauden ◽  
Sean Crosson ◽  
I. H. M. van Stokkum ◽  
Rienk van Grondelle ◽  
Keith Moffat ◽  
...  
Keyword(s):  
Low Temperature ◽  
Avena Sativa ◽  
Spectroscopic Characterization ◽  
Time Resolved

Spectroscopic Characterization of Ion-Implanted GaN

2002 ◽  
Vol 743 ◽  
Author(s):  
L. Chen ◽  
B. J. Skromme
Keyword(s):  
Low Temperature ◽  
High Purity ◽  
Spectroscopic Characterization ◽  
Acceptor Pair ◽  
Donor Acceptor ◽  
Optical Activation ◽  
Donor Acceptor Pair ◽  
Low Temperature Photoluminescence ◽  
Do So

ABSTRACTWe investigate implantation of high purity HVPE GaN with Mg, Be, C, Zn, Cd, Ca, N, O, P, As, Ne, and Ar. After annealing at 1300 °C, the material is characterized using low temperature photoluminescence (PL). The Mg acceptors exhibit much better optical activation than Be, C, Zn, Cd, or Ca acceptors implanted and annealed under the same conditions. Acceptor-bound exciton peaks and well-resolved donor-acceptor pair bands are observed for both Mg and Zn. A broad peak centered near 2.78 eV is obtained for Cd, confirming that it is deeper than Zn. Isoelectronic As or P exhibit sharp no-phonon bound exciton lines at 2.952 and 3.200 eV, respectively. Defect-related bands centered at 2.2 and 2.35 eV are studied. Both Be and C strongly enhance the yellow (2.2 eV) PL band, but no other impurities do so, including O.

scholarly journals Electrochemical and spectroscopic characterization of the conversion of the 7Fe into the 8Fe form of ferredoxin III from Desulfovibrio africanus. Identification of a [4Fe–4S] cluster with one non-cysteine ligand

1989 ◽  
Vol 264 (1) ◽  
pp. 275-284 ◽  
Author(s):  
S J George ◽  
F A Armstrong ◽  
E C Hatchikian ◽  
A J Thomson
Keyword(s):  
Amino Acid ◽  
Pyrolytic Graphite ◽  
Direct Electrochemistry ◽  
Spectroscopic Characterization ◽  
Cysteine Residue ◽  
Side Chain ◽  
Iron Protein ◽  
Plausible Model ◽  
The One

Desulfovibrio africanus ferredoxin III is a protein (Mr 6585) containing one [3Fe-4S]1+,0 and one [4Fe-4S]2+,1+ core cluster when aerobically isolated. The amino acid sequence contains only seven cysteine residues, the minimum required to ligand these two clusters. Cyclic voltammery by means of direct electrochemistry at a pyrolytic-graphite-‘edge’ electrode promoted by neomycin shows that, when reduced, the [3Fe-4S]0 centre reacts rapidly with Fe(II) ion to form a [4Fe-4S]2+ cluster. The latter, which can be reduced at a redox potential similar to that of the other [4Fe-4S] cluster, must include non-thiolate ligation. We propose that the carboxylate side chain of aspartic acid-14 is the most likely candidate, since this amino acid occupies the position of a cysteine residue in the sequence typical of an 8Fe ferredoxin. The magnetic properties at liquid-He temperature of this novel cluster, studied by low-temperature magnetic-c.d. and e.p.r. spectroscopy, are diamagnetic in the oxidized state and S = 3/2 in the one-electron-reduced state. This cluster provides a plausible model for the ligation states of the [4Fe-4S]1+ core in the S = 3/2 cluster of the iron protein of nitrogenase and in Bacillus subtilis glutamine:phosphoribosyl pyrophosphate amidotransferase.

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