4D4X:
reference: Hydrogen bonding of the dissociated histidine ligand is not required for formation of a proximal NO adduct in cytochrome c'., Ghafoor DD, Kekilli D, Abdullah GH, Dworkowski FS, Hassan HG, Wilson MT, Strange RW, Hough MA, J Biol Inorg Chem. 2015 Sep;20(6):949-56. doi: 10.1007/s00775-015-1278-y. Epub, 2015 Jun 23. PMID: 26100643

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