3ABK:
reference: X-ray structure of the NO-bound Cu(B) in bovine cytochrome c oxidase., Ohta K, Muramoto K, Shinzawa-Itoh K, Yamashita E, Yoshikawa S, Tsukihara T, Acta Crystallogr Sect F Struct Biol Cryst Commun. 2010 Mar 1;66(Pt, 3):251-3. Epub 2010 Feb 23. PMID: 20208153

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