2VHB:
reference: Unusual structure of the oxygen-binding site in the dimeric bacterial hemoglobin from Vitreoscilla sp., Tarricone C, Galizzi A, Coda A, Ascenzi P, Bolognesi M, Structure 1997 Apr 15;5(4):497-507. PMID: 9115439

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