Isolation of the FeMo cofactor from nitrogenase is done through centrifugal sedimentation of nitrogenase into the MoFe protein and the Fe protein. The FeMo cofactor is extracted by treating the MoFe protein with acids. The first extraction is done with N,N-dimethylformamide and the second by a mixture of N-methylformamide and NaHPO before final sedimentation by centrifugation.