Oxidative inactivation of the molybdenum-iron-protein component of nitrogenase from clostridium pasteurianum

1979 ◽  
Vol 26 (2) ◽  
Author(s):  
Carlos Gomez-Moreno ◽  
KE Bacon
Keyword(s):  
Protein Component ◽  
Clostridium Pasteurianum ◽  
Molybdenum Iron Protein ◽  
Iron Protein ◽  
Oxidative Inactivation

scholarly journals E.p.r.-spectroscopic studies on the molybdenum–iron site of nitrogenase from Clostridium pasteurianum

1989 ◽  
Vol 262 (1) ◽  
pp. 349-352 ◽  
Author(s):  
G N George ◽  
R E Bare ◽  
H Y Jin ◽  
E I Stiefel ◽  
R C Prince
Keyword(s):  
Hyperfine Coupling ◽  
Double Resonance ◽  
Spectroscopic Studies ◽  
Clostridium Pasteurianum ◽  
Iron Site ◽  
Electron Nuclear Double Resonance ◽  
Molybdenum Iron Protein ◽  
Iron Protein ◽  
Hyperfine Splittings

The e.p.r. spectroscopy of the nitrogenase molybdenum-iron protein from Clostridium pasteurianum was re-investigated. The sharpness of the delta Ms = +/- 3 g′z peak from the +/- 3/2 Kramer's doublet enables the observation and quantification of incompletely resolved hyperfine splittings from the stable magnetic nuclei 95Mo and 57Fe in samples enriched in these isotopes. No couplings to 1H or 17O could be discerned by examination of spectra from samples exchanged into 2H2O and H2(17)O respectively. Simulation of the spectrum from 95Mo-enriched samples yields a hyperfine coupling of 2.9 MHz, and indicates that the earlier electron-nuclear-double-resonance-derived estimate of 8.1 +/- 0.2 MHz is substantially in error.

scholarly journals The photoreduction of nitrogenase

1993 ◽  
Vol 290 (2) ◽  
pp. 627-631 ◽  
Author(s):  
Druzhinin SYu ◽  
L A Syrtsova ◽  
A M Uzenskaja ◽  
G I Likhtenstein
Keyword(s):  
Atpase Activity ◽  
Azotobacter Vinelandii ◽  
Electron Flux ◽  
Protein Component ◽  
Photochemical Reduction ◽  
Total Electron ◽  
Molybdenum Iron Protein ◽  
Iron Protein ◽  
Reduction Activity ◽  
Substrate Reduction

The photoreduction, without reductant dithionite, of N2 to NH3 or acetylene to ethylene catalysed by nitrogenase in the presence of Mg2+. ATP, eosin and NADH in the light has been established. There is an optimum NADH concentration for each particular eosin concentration. When the ratio of the iron protein component of nitrogenase from Azotobacter vinelandii (Av2)/the molybdenum-iron protein component of nitrogenase from A. vinelandii (Av1) is equal to 3 for 4 x 10(-5) M eosin the optimum NADH concentration is 5 x 10(-4) M. The rate of photoreduction (per one electron) of acetylene or N2 under identical conditions was shown to be similar. The photoreductant-dependent ATPase activity, in the presence of a given photochemical system in the light, was revealed. Eosin is shown to be the inhibitor of the coupling site. Concentrations of 8 x 10(-6) -1 x 10(-4) M eosin do not inhibit the ATPase activity. The inhibition of substrate-reduction activity depends on the ratio of the nitrogenase components. Under conditions where the Av2/Av1 ratio is equal to 1 the rate of photochemical reduction is higher than in the presence of dithionite: the total electron flux through nitrogenase being increased 2.2-fold. We suggest that in this case the nitrogenase complex (1:1) works without dissociation.

Electron transfer and half-reactivity in nitrogenase

2011 ◽  
Vol 39 (1) ◽  
pp. 201-206 ◽  
Author(s):  
Thomas A. Clarke ◽  
Shirley Fairhurst ◽  
David J. Lowe ◽  
Nicholas J. Watmough ◽  
Robert R. Eady
Keyword(s):  
Electron Transfer ◽  
Protein Molecule ◽  
Stopped Flow ◽  
Protein Binding Sites ◽  
Molybdenum Iron Protein ◽  
Iron Protein ◽  
Mofe Protein ◽  
Fe Protein ◽  
Rapid Quench ◽  
Important Enzyme

Nitrogenase is a globally important enzyme that catalyses the reduction of atmospheric dinitrogen into ammonia and is thus an important part of the nitrogen cycle. The nitrogenase enzyme is composed of a catalytic molybdenum–iron protein (MoFe protein) and a protein containing an [Fe4–S4] cluster (Fe protein) that functions as a dedicated ATP-dependent reductase. The current understanding of electron transfer between these two proteins is based on stopped-flow spectrophotometry, which has allowed the rates of complex formation and electron transfer to be accurately determined. Surprisingly, a total of four Fe protein molecules are required to saturate one MoFe protein molecule, despite there being only two well-characterized Fe-protein-binding sites. This has led to the conclusion that the purified Fe protein is only half-active with respect to electron transfer to the MoFe protein. Studies on the electron transfer between both proteins using rapid-quench EPR confirmed that, during pre-steady-state electron transfer, the Fe protein only becomes half-oxidized. However, stopped-flow spectrophotometry on MoFe protein that had only one active site occupied was saturated by approximately three Fe protein equivalents. These results imply that the Fe protein has a second interaction during the initial stages of mixing that is not involved in electron transfer.

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