_EC 1.12.2.- With a cytochrome as acceptor. 69 PDB entries  
EC 1.-.-.- Oxidoreductases. [21,435 PDB entries]
EC 1.12.-.- Acting on hydrogen as donors. [251 PDB entries]
EC 1.12.2.- With a cytochrome as acceptor. [69 PDB entries]
EC 1.12.2.1 cytochrome-c3 hydrogenase. [69 PDB entries]