6FF5:
reference: X-ray structure of bovine heart cytochrome c at high ionic strength., Merlino A, Biometals. 2018 Mar 7. pii: 10.1007/s10534-018-0090-x. doi:, 10.1007/s10534-018-0090-x. PMID: 29516298

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