4M4L:
reference: Towards accurate structural characterization of metal centres in protein crystals: the structures of Ni and Cu T6 bovine insulin derivatives., Frankaer CG, Mossin S, Stahl K, Harris P, Acta Crystallogr D Biol Crystallogr. 2014 Jan;70(Pt 1):110-22. doi:, 10.1107/S1399004713029040. Epub 2013 Dec 24. PMID: 24419384

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