scholarly journals Azotobacter chroococcum 7Fe ferredoxin. Two pH-dependent forms of the reduced 3Fe clusters and its conversion to a 4Fe cluster

1984 ◽  
Vol 224 (1) ◽  
pp. 247-251 ◽  
Author(s):  
S J George ◽  
A J M Richards ◽  
A J Thomson ◽  
M G Yates
Keyword(s):  
Magnetic Circular Dichroism ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Iron Chelator ◽  
Anaerobic Treatment ◽  
Azotobacter Chroococcum ◽  
Resonance Spectroscopy ◽  
Paramagnetic Resonance ◽  
High Affinity ◽  
Ph Dependent ◽  
Electron Paramagnetic

Ferredoxin from Azotobacter chroococcum has been studied by low-temperature magnetic-circular-dichroism and electron-paramagnetic-resonance spectroscopy. When aerobically isolated ferredoxin contains a [3Fe-4S] and [4Fe-4S] cluster. Anaerobic treatment with dithionite in the presence of ethanediol reduces the [3Fe-4S] cluster to give two spectroscopically distinct forms RI and RII which are reversibly interconvertible with a pKa approximately 7.5. The higher-pH form, RII, has a high affinity for ferrous ion and converts readily to a [4Fe-4S]1+ cluster, scavenging iron from the medium. The presence of the iron chelator EDTA inhibits this conversion.

scholarly journals Some magnetic properties of Pseudomonas cytochrome oxidase

1979 ◽  
Vol 177 (1) ◽  
pp. 29-39 ◽  
Author(s):  
T A Walsh ◽  
M K Johnson ◽  
C Greenwood ◽  
D Barber ◽  
J P Springall ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Cytochrome C ◽  
Cytochrome Oxidase ◽  
Magnetic Circular Dichroism ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Resonance Spectroscopy ◽  
Parallel Study ◽  
Paramagnetic Resonance ◽  
Redox States ◽  
Electron Paramagnetic

The magnetic properties of the haem groups of Pseudomonas cytochrome oxidase and its cyanide-bound derivatives were studied in both the oxidized and reduced states by means of m.c.d. (magnetic circular dichroism) at low temperatures. In addition, the oxidized forms of the enzyme were also investigated by e.p.r. (electron-paramagnetic-resonance) spectroscopy, and a parallel study, using both e.p.r. and m.c.d., was made on Pseudomonas cytochrome c-551 to aid spectral assignments. For ascorbate-reduced Pseudomonas cytochrome oxidase, the temperature-independence of those features in the m.c.d. spectrum corresponding to the haem c, and the temperature-dependence of those signals corresponding to the haem d1, showed the former to be low-spin and the latter to be high-spin (s = 2). However, addition of cyanide to the reduced enzyme gave a form of the protein that was completely low-spin. The e.p.r. and m.c.d. sectra of oxidized Pseudomonas cytochrome oxidase and its cyanide derivative were consistent with the haem c and d1 components being low-spin in both cases. Pseudomonas cytochrome c-551 was found to be low-spin in both its oxidized and reduced redox states.

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