4KNT:
reference: Characterization of a Nitrite Reductase Involved in Nitrifier Denitrification., Lawton TJ, Bowen KE, Sayavedra-Soto LA, Arp DJ, Rosenzweig AC, J Biol Chem. 2013 Jul 15. PMID: 23857587

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