1WPM:
reference: Structural studies of metal ions in family II pyrophosphatases: the requirement for a Janus ion., Fabrichniy IP, Lehtio L, Salminen A, Zyryanov AB, Baykov AA, Lahti R, Goldman A, Biochemistry 2004 Nov 16;43(45):14403-11. PMID: 15533045

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