INFRARED-ANALYSIS OF LIGAND-INDUCED AND OXIDATION-INDUCED CONFORMATIONAL-CHANGES IN HEMOGLOBINS AND MYOGLOBINS

Effects of the binding of O-2 and CO to heme iron (II) of deoxy forms and of the oxidation of deoxy forms to aquoiron (III) complexes on the infrared spectra of hemoglobins and myoglobins have been examined, Sp ectra were measured for aqueous solutions 3-4 mM in heme of human, bov ine, and equine hemoglobins and sperm whale, bovine, and equine myoglo bins in 10 mM sodium phosphate buffer, pH 7.4, at 20 degrees C, All li gand binding and oxidation reactions resulted in similar spectral shif ts in the region 1665 to 1670 cm(-1), a portion of the amide I region assignable to beta-turn structure, There were no other significant cha nges in the amide I region, a finding consistent with no other alterat ions in secondary structure, The major bands near 1655 cm(-1) associat ed with alpha-helices were consistently at 2 cm(-1) lower wavenumber f or myoglobins than for hemoglobins, The changes in solution infrared s pectra observed in this study may result at least in part from conform ational changes at the FG corner associated with movements of F and E helices that have been noted previously in crystal structures. (C) 199 5 Academic Press, Inc.