6C93:
reference: Non-covalent interactions dominate dynamic heme distortion in cytochrome P450 4B1., Jennings GK, Hsu MH, Shock LS, Johnson EF, Hackett JC, J Biol Chem. 2018 Jun 1. pii: RA118.004044. doi: 10.1074/jbc.RA118.004044. PMID: 29858244

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