Nitrogenase of Azotobacter chroococcum. Kinetics of the reduction of oxidized iron-protein by sodium dithionite.

The Biochemical journal ·Vol. 155 ·No. 1 ·1976-04-01 ·Pages 137-44

Thorneley RN, Yates MG, Lowe DJ

Abstract

The kinetics of the reduction of oxidized Fe-protein of nitrogenase from Azotobacter chroococcum by sodium dithionite were studied by stopped-flow and rapid-freezing e.p.r. (electron-paramagnetic-resonance) spectroscopy. The appearance of the gav. = 1.94 e.p.r. signal (0.24 electron integrated intensity/mol) was associated with a one-electron reduction by SO2--with k greater than 10(8)M-1-S-1 at 23 degrees C. A value of k = 1.75s-1 was obtained for the rate of dissociation of S2O42- into 2SO2-- at 23 degrees C. Further reductions by SO2-- occurred in three slower phases with rate constants in the range 10(4) -10(6)M-1-S-1. These latter phases have no corresponding e.p.r. signal changes and are probably associated with enzymically inactive protein. The high rate of reduction by SO2-- of the Fe-protein alone (k greater than 10(8)M-1-S-1) relative to the rate of oxidation of the Fe-protein in the catalytically active Fe:Mo-Fe protein complex (k = 2.2 X 1O(2)s-1) and the observation that in the steady state the Fe-protein is substantially oxidized means that at normal assay concentrations another reaction must limit the rate of reduction of Fe-protein during turnover.

MeSH Terms

Adenosine Triphosphate/pharmacology Azotobacter/enzymology Binding Sites Dithionite/pharmacology Electron Spin Resonance Spectroscopy Iron/metabolism Kinetics Magnesium/pharmacology Metalloproteins/metabolism Nitrogenase/metabolism Oscillometry Oxidation-Reduction Oxygen/pharmacology Sulfites/pharmacology

Chemicals

Metalloproteins Sulfites Dithionite Adenosine Triphosphate Iron Nitrogenase Magnesium Oxygen

Authors & Affiliations

3 authors, click to expand affiliations / ORCID

Thorneley R N

Yates M G

Lowe D J

References (21)

21 references, click to expand

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Article Info

Journal

The Biochemical journal

Abbr.

Biochem J

ISSN

0264-6021

DOI

10.1042/bj1550137

Published

1976-04-01

Pages

137-44

Language

English

Region

England

NLM ID

2984726R

PMCID

PMC1172810

Subset

External Links

PubMed source DOI: 10.1042/bj1550137 PMC Full Text View journal details

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Nitrogenase of Azotobacter chroococcum. Kinetics of the reduction of oxidized iron-protein by sodium dithionite.

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