4NCQ:
reference: Nickel superoxide dismutase: structural and functional roles of His1 and its H-bonding network., Ryan KC, Guce AI, Johnson OE, Brunold TC, Cabelli DE, Garman SC, Maroney MJ, Biochemistry. 2015 Feb 3;54(4):1016-27. doi: 10.1021/bi501258u. Epub 2015 Jan 21. PMID: 25580509

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