2MHB:
reference: The structure of horse methaemoglobin at 2-0 A resolution., Ladner RC, Heidner EJ, Perutz MF, J Mol Biol 1977 Aug 15;114(3):385-414. PMID: 561852

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