Open AccessThe importance of quantitative Mössbauer spectroscopy of MoFe‐protein from Azotobacter vinelandii
Author(s) -
DUNHAM William R.,
HAGEN Wilfred R.,
BRAAKSMA Arnold,
GRANDE Hans J.,
HAAKER Huub
Publication year - 1985
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1985.tb08679.x
Subject(s) - azotobacter vinelandii , mössbauer spectroscopy , chemistry , dithionite , spectral line , crystallography , absorption spectroscopy , quadrupole , stoichiometry , nitrogenase , analytical chemistry (journal) , atomic physics , nitrogen , physics , nitrogen fixation , biochemistry , enzyme , organic chemistry , quantum mechanics , astronomy , chromatography
The Mössbauer spectra of MoFe‐protein of Azotobacter vinelandii , as isolated under dithionite and taken at temperatures from 125 K to 175 K, are the sums of four resolved quadrupole doublets. Our results indicate that the currently accepted interpretation of these doublets can be questioned. Our data reduction method converts the Mössbauer transmission spectra to source lineshape deconvolved absorption spectra linear in iron. We used these absorption spectra to determine the stoichiometry of the Fe clusters in MoFe‐protein and we obtained much better fits if we assumed that there are four iron atoms in the ‘Fe 2+ ’ doublet, two iron atoms in the ‘S’ doublet, twelve iron atoms in the ‘D’ doublet and sixteen iron atoms in the ‘M’ doublet. Therefore we propose that the MoFe‐cofactor contains one molybdenum and eight iron atoms (‘M’). We also argue that none of the previous Mössbauer spectroscopic studies have been perfomed on the highest‐activity preparation now obtainable, nor has there been any study to prove that the Mössbauer spectra are independent of activity. We consider that the Mössbauer spectroscopic studies of the MoFe‐protein of nitrogenase are a re‐opened and unsolved problem.