 The [Ni-Fe] active site oxidized hydrogen gas which transfers electrons to a FMN-a cofactor, then to a [Fe-S] cluster relay of the small hydrogenase subunit and the reductase module, then to another FMN-b cofactor and finally to NAD+.The reducing equivalences are then used for fixing carbon dioxide when "C. necator" is growing autotrophically.The active site of the SH of "C. necator" H16 has been extensively studied because "C. necator" H16 can be produced in large amounts, can be genetically manipulated, and can be analyzed with spectrographic techniques.