3AX9:
reference: Protein conformational gating of enzymatic activity in xanthine oxidoreductase., Ishikita H, Eger BT, Okamoto K, Nishino T, Pai EF, J Am Chem Soc. 2012 Jan 18;134(2):999-1009. Epub 2011 Dec 29. PMID: 22145797

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