2ZPP:
reference: An abnormal pK(a) value of internal histidine of the insulin molecule revealed by neutron crystallographic analysis., Ishikawa T, Chatake T, Morimoto Y, Maeda M, Kurihara K, Tanaka I, Niimura N, Biochem Biophys Res Commun. 2008 Nov 7;376(1):32-5. Epub 2008 Aug 24. PMID: 18725203

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