1FEH:
reference: X-ray crystal structure of the Fe-only hydrogenase (CpI) from Clostridium pasteurianum to 1.8 angstrom resolution., Peters JW, Lanzilotta WN, Lemon BJ, Seefeldt LC, Science 1998 Dec 4;282(5395):1853-8. PMID: 9836629

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