2 Fe(III)-[cytochrome c3] + H2 = 2 Fe(II)-[cytochrome c3] + 2 H(+) Binds 1 [3Fe-4S] cluster. Binds 2 [4Fe-4S] clusters. Heterodimer of a large and a small subunit. Belongs to the [NiFe]/[NiFeSe] hydrogenase small subunit family.