2PRQ:
reference: X-ray crystallographic characterization of the Co(II)-substituted Tris-bound form of the aminopeptidase from Aeromonas proteolytica., Munih P, Moulin A, Stamper CC, Bennett B, Ringe D, Petsko GA, Holz RC, J Inorg Biochem. 2007 Aug;101(8):1099-1107. Epub 2007 Apr 11. PMID: 17574677

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