4XYY:
reference: Structural Characterization of the Complex between Hen Egg-White Lysozyme and Zr -Substituted Keggin Polyoxometalate as Artificial Protease., Sap A, De Zitter E, Van Meervelt L, Parac-Vogt TN, Chemistry. 2015 Jul 14. doi: 10.1002/chem.201501998. PMID: 26179600

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