3HB3:
reference: High resolution crystal structure of Paracoccus denitrificans cytochrome c oxidase: New insights into the active site and the proton transfer pathways., Koepke J, Olkhova E, Angerer H, Muller H, Peng G, Michel H, Biochim Biophys Acta. 2009 Jun;1787(6):635-45. Epub 2009 Apr 15. PMID: 19374884

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