5GYR:
reference: Formation and carbon monoxide-dependent dissociation of Allochromatium vinosum cytochrome c' oligomers using domain-swapped dimers., Yamanaka M, Hoshizumi M, Nagao S, Nakayama R, Shibata N, Higuchi Y, Hirota S, Protein Sci. 2017 Mar;26(3):464-474. doi: 10.1002/pro.3090. Epub 2017 Feb 14. PMID: 27883268

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