title: Structural characterization of the myoglobin active site using infrared crystallography.
abstract: We use polarized IR absorption on single crystals to determine the orientation of carbon monoxide bound at the active site of myoglobin, and conclude that the C-O bond lies approximately 7 degrees from the normal to the mean plane of the heme. This result disagrees with much larger angular displacements reported in structural models derived from X-ray and neutron diffraction measurements. The insensitivity of the IR-derived orientation to changes in pH or crystal packing contrasts with the wide variations in CO orientation among diffraction-based models and suggests that the latter are in error. The small energies required to displace the C-O bond 7 degrees from its energetically preferred upright geometry suggest that distortion of the surrounding protein, rather than the relatively undeformable Fe-C-O unit, is the main steric mechanism inhibiting CO binding to myoglobin.
authors.affiliation: Department of Physics and Center for Interdisciplinary Research on Complex Systems, Northeastern University, Boston, MA 02115, USA.
authors.forename: J T
authors.initials: JT
authors.lastname: Sage
authors.forename: W
authors.initials: W
authors.lastname: Jee
mesh_terms: D000818:Animals; D001665:Binding Sites; D002248:Carbon Monoxide / Q000378:metabolism; D018360:Crystallography, X-Ray / Q000379:methods; D009211:Myoglobin / Q000737:chemistry* / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D013055:Spectrophotometry, Infrared / Q000379:methods; D014907:Whales
chemical_list: D009211:Myoglobin; D002248:Carbon Monoxide; D010100:Oxygen