3D7O:
reference: The nitrite anion binds to human hemoglobin via the uncommon O-nitrito mode., Yi J, Safo MK, Richter-Addo GB, Biochemistry. 2008 Aug 12;47(32):8247-9. Epub 2008 Jul 17. PMID: 18630930

This OCA Structure page
uses Jmol, developed by the Jmol Development Team (documentation).