The uptake hydrogenase
consists of at least two subunits (encoded by hupS and hupL)
oxidizing the H2 evolved by nitrogenase. The bidirectional Hoxhydrogenase
consists of a hydrogenase part (encoded by hoxY
and hoxH) and a diaphorase part (encoded by hoxE, hoxU and hoxF).
The enzyme may catalyze both the production and utilization of H2
(Tamagnini et al., 2007; Phunpruch et al., 2006).