Evidence for Electron Transfer from the Nitrogenase Iron Protein to the Molybdenum−Iron Protein without MgATP Hydrolysis:  Characterization of a Tight Protein−Protein Complex†

Biochemistry ◽  
1996 ◽  
Vol 35 (22) ◽  
pp. 7188-7196 ◽  
Author(s):  
William N. Lanzilotta ◽  
Karl Fisher ◽  
Lance C. Seefeldt
Keyword(s):  
Electron Transfer ◽  
Protein Complex ◽  
Molybdenum Iron Protein ◽  
Iron Protein ◽  
Nitrogenase Iron Protein

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.

Structural characterization of the nitrogenase molybdenum-iron protein with the substrate acetylene trapped near the active site

2018 ◽  
Vol 180 ◽  
pp. 129-134 ◽  
Author(s):  
Stephen M. Keable ◽  
Jacopo Vertemara ◽  
Oleg A. Zadvornyy ◽  
Brian J. Eilers ◽  
Karamatullah Danyal ◽  
...  
Keyword(s):  
Structural Characterization ◽  
Active Site ◽  
Molybdenum Iron Protein ◽  
Iron Protein

scholarly journals Characterization of an oxygen-stable nitrogenase complex isolated from Azotobacter chroococcum

1979 ◽  
Vol 181 (3) ◽  
pp. 569-575 ◽  
Author(s):  
R L Robson
Keyword(s):  
Density Gradient Centrifugation ◽  
Gradient Centrifugation ◽  
Sucrose Density Gradient ◽  
Azotobacter Chroococcum ◽  
Sucrose Density Gradient Centrifugation ◽  
Molybdenum Iron Protein ◽  
Iron Protein ◽  
Protective Proteins

In crude cell-free extracts of Azotobacter chroococcum, nitrogenase was much less sensitive to irreversible inactivation by O2 than was the purified enzyme. When nitrogenase was partially purified by anaerobic discontinuous sucrose-density-gradient centrifugation, O2-tolerance was retained. This preparation was considerably enriched in four polypeptides, three of which were derived from the Mo-Fe(molybdenum-iron) protein and Fe (iron) protein of nitrogenase. The fourth was purified to homogeneity and shown to be an iron-sulphur protein (mol.wt. 14000) probably containing a 2Fe–2S centre. When this protein was added to purified nitrogenase, the enzyme was rendered O2-tolerant, through stabilization was Mg2+-dependent. The isolated O2-tolerant nitrogenase was an equimolar stoicheiometric complex between the MO–Fe, Fe and protective proteins. It is likely that the formation of this complex in vivo is the mechanism of ‘conformational protection’ in this organism.

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