2MGJ:
reference: High-resolution crystal structures of distal histidine mutants of sperm whale myoglobin., Quillin ML, Arduini RM, Olson JS, Phillips GN Jr, J Mol Biol 1993 Nov 5;234(1):140-55. PMID: 8230194

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