3VKT:
reference: The reductive reaction mechanism of tobacco nitrite reductase derived from a combination of crystal structures and ultraviolet-visible microspectroscopy., Nakano S, Takahashi M, Sakamoto A, Morikawa H, Katayanagi K, Proteins. 2012 Aug;80(8):2035-45. doi: 10.1002/prot.24094. Epub 2012 May 17. PMID: 22499059

This OCA Structure page
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