This is one of three S.flexneri hydrogenases synthesized in response to different physiological conditions. HYD1 is believed to have a role in hydrogen cycling during fermentative growth (By similarity). A + H2 = AH2 Binds 1 [3Fe-4S] cluster. Binds 2 [4Fe-4S] clusters. Heterodimer of a large and a small subunit. Predicted to be exported by the Tat system. The position of the signal peptide cleavage has not been experimentally proven. Belongs to the [NiFe]/[NiFeSe] hydrogenase small subunit family.