 The MBH in "C. necator" is not inhibited by CO and is tolerant to oxygen.The NAD+-reducing hydrogenase (soluble hydrogenase, SH) creates a NADH-reducing equivalence by oxidizing hydrogen gas.The SH is a heterohexameric protein with two subunits making up the large and small subunits of the [Ni-Fe] hydrogenase and the other two subunits comprising a reductase module similar to the one of Complex I.