3NG6:
reference: An order-disorder transition plays a role in switching off the Root effect in fish hemoglobins., Vergara A, Vitagliano L, Merlino A, Sica F, Marino K, Verde C, di Prisco G, Mazzarella L, J Biol Chem. 2010 Jul 7. PMID: 20610398

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