Protocols for cofactor isolation of nitrogenase.

The iron-molybdenum cofactor (FeMoco) of the nitrogenase MoFe protein has remained a focal point in the field of bioinorganic chemistry for decades. This unique metal cluster has long been regarded as the actual site of dinitrogen reduction, and it is structurally complex and chemically unprecedented. A detailed characterization of the isolated FeMoco is crucial for elucidating the physiochemical properties of this biologically important cofactor. Such a study requires an effective technique to extract FeMoco intact, and in high yield, from the MoFe protein. A method involving the acid treatment of the MoFe protein and the subsequent extraction of FeMoco into an organic solvent was developed over 30 years ago and has been improved upon ever since. FeMoco isolated by this strategy is catalytically active and spectrally interesting, which provides a useful platform for future structure-function analyses of this unique cofactor. A general working protocol for FeMoco isolation is described in this chapter, along with some of the major modifications reported in the past years.