Catalyzes the reversible oxidoreduction of molecular hydrogen, in conjunction with a specific electron acceptor, cytochrome c3. 2 Fe(III)-[cytochrome c3] + H2 = 2 Fe(II)-[cytochrome c3] + 2 H(+) Heterodimer of a large and a small subunit. Perhaps the leader of the small subunit serves as a transport vehicle for both subunits. Belongs to the [NiFe]/[NiFeSe] hydrogenase large subunit family.