The importance of quantitative Mossbauer spectroscopy of MoFe-protein from Azotobacter vinelandii

Abstract

The Moessbauer spectra of MoFe-protein of A. vinelandii, as isolated under dithionite and taken at temperatures from 125.degree.-175.degree. K,are the sums of 4 resolved quadrupole doublets. These results indicate that the currently accepted interpretation of these doublets can be questioned. This data reduction method converts the Moessbauer transmission spectra to source lineshape deconvolved absorption spectra linear in Fe. These absorption spectra were used to determine the stoichiometry of the Fe clusters in MoFe-protein and much better fits were obtained that there are 4 Fe atoms in the Fe2+ doublet, 2 Fe atoms in the S doublet, 12 Fe atoms in the D doublet and 16 Fe atoms in the M doublet. It is proposed that the MoFe-cofactor contains 1 Mo and 8 Fe atoms (M). Since none of the previous Moessbauer spectroscopic studies have been performed on the highest-activity preparation now obtainable, nor has there been any study to prove that the Moessbauer spectra are independent of activity, it is considered that the Moessbauer spectroscopic studies of the MoFe-protein of nitrogenase (EC 1.18.2.1) are a re-opened and unsolved problem.