In enzymology, a cytochrome-c3 hydrogenase (EC 1.12.2.1) is an enzyme that catalyzes the chemical reaction

2 H₂ + ferricytochrome c₃ ${\displaystyle \rightleftharpoons }$ 4 H⁺ + ferrocytochrome c₃

Thus, the two substrates of this enzyme are H₂ and ferricytochrome c3, whereas its two products are H⁺ and ferrocytochrome c3.

This enzyme belongs to the family of oxidoreductases, specifically those acting on hydrogen as donor with a cytochrome as acceptor. The systematic name of this enzyme class is hydrogen:ferricytochrome-c3 oxidoreductase. Other names in common use include H2:ferricytochrome c3 oxidoreductase, cytochrome c3 reductase, cytochrome hydrogenase, and hydrogenase [ambiguous]. It has 3 cofactors: iron, Nickel, and Iron-sulfur.

Structural studies

As of late 2007, 19 structures have been solved for this class of enzymes, with PDB accession codes 1FRV, 1H2R, 1UBH, 1UBJ, 1UBK, 1UBL, 1UBM, 1UBO, 1UBR, 1UBT, 1UBU, 1WUH, 1WUI, 1WUJ, 1WUK, 1WUL, 1YQ9, 1YQW, and 1YRQ.