 The differences between the regulatory hydrogenase, membrane-bound hydrogenase, soluble hydrogenase and actinobacterial hydrogenase in "C. necator" are described below.The first hydrogenase is a regulatory hydrogenase (RH) that signals to the cell hydrogen is present.The RH is a protein containing large and small [Ni-Fe] hydrogenase subunits attached to a histidine protein kinase subunit.