1QQU:
reference: Crystal structure at 1.63 A resolution of the native form of porcine beta-trypsin: revealing an acetate ion binding site and functional water network., Johnson A, Gautham N, Pattabhi V, Biochim Biophys Acta 1999 Nov 16;1435(1-2):7-21. PMID: 10561533

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