2OIF:
reference: Plant hemoglobins: a molecular fossil record for the evolution of oxygen transport., Hoy JA, Robinson H, Trent JT 3rd, Kakar S, Smagghe BJ, Hargrove MS, J Mol Biol. 2007 Aug 3;371(1):168-79. Epub 2007 May 18. PMID: 17560601

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