Electron Paramagnetic Resonance and Magnetic Circular Dichroism Spectra of the Nitrogenase M Cluster Precursor Suggest Sulfur Migration upon Oxidation: A Proposal for Substrate and Inhibitor Binding

Document Type


Publication Date



The active site of the nitrogen-fixing enzyme Mo-nitrogenase is the M cluster ([MoFe S C⋅R-homocitrate]), also known as the FeMo cofactor or FeMoco. The biosynthesis of this highly complex metallocluster involves a series of proteins. Among them, NifB, a radical-SAM enzyme, is instrumental in the assembly of the L cluster ([Fe S C]), a precursor and all-iron core of the M cluster. In the absence of sulfite, NifB assembles a precursor form of the L cluster called the L* cluster ([Fe S C]), which lacks the final ninth sulfur. EPR and MCD spectroscopies are used to probe the electronic structures of the paramagnetic, oxidized forms of both the L and L* clusters, labeled L and [L*] . This study shows that both L and [L*] have nearly identical EPR and MCD spectra, thus suggesting that the two clusters have identical structures upon oxidation; in other words, a sulfur migrates away from L following oxidation, thereby rendering the cluster identical to [L*] . It is proposed that a similar migration could occur to the M cluster upon oxidation, and that this is an instrumental part of both M cluster formation and nitrogenase substrate/inhibitor binding.

Publication Source (Journal or Book title)

Chembiochem : a European journal of chemical biology

First Page


Last Page


This document is currently not available here.