1UX8:
reference: The truncated oxygen-avid hemoglobin from Bacillus subtilis: X-ray structure and ligand binding properties., Giangiacomo L, Ilari A, Boffi A, Morea V, Chiancone E, J Biol Chem. 2005 Mar 11;280(10):9192-202. Epub 2004 Dec 7. PMID: 15590662

This OCA Structure page
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