4MEC:
reference: Distal regulation of heme binding of heme oxygenase-1 mediated by conformational fluctuations., Harada E, Sugishima M, Harada J, Fukuyama K, Sugase K, Biochemistry. 2015 Jan 20;54(2):340-8. doi: 10.1021/bi5009694. Epub 2014 Dec 26. PMID: 25496210

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