 However, no crystal structure is currently available for the "C. necator" H16 soluble hydrogenase in the presence of oxygen to determine the interactions of the active site with the rest of the protein.The [Ni-Fe] hydrogenase from "Desulfovibrio vulgaris" and "D. gigas" have similar protein structures to each other and represent typical [Ni-Fe] hydrogenases.The large subunit contains the [Ni-Fe] active site buried deep in the core of the protein and the small subunit contains [Fe-S] clusters.