Fe-heme conformations in ferric myoglobin.
X-ray absorption near-edge structure (XANES) spectra of ferric myoglobin from horse heart have been acquired as a function of pH (between 5.3 and 11.3). At pH = 11.3 temperature-dependent spectra (between 20 and 293 K) have been collected as well. Experimental data solve three main conformations of the Fe-heme: the first, at low pH, is related to high-spin aquomet-myoglobin (Mb+OH2). The other two, at pH 11.3, are related to hydroxymet-myoglobin (Mb+OH-), and are in thermal equilibrium, corresponding to high- and low-spin Mb+OH-. The structure of the three Fe-heme conformations has been assigned according to spin-resolved multiple scattering simulations and fitting of the XANES data. The chemical transition between Mb+OH2 and high-spin Mb+OH-, and the spin transition of Mb+OH-, are accompanied by changes of the Fe coordination sphere due to its movement toward the heme plane, coupled to an increase of the axial asymmetry.
Della Longa
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Dept. Medicina Sperimentale and INFM, Università dell'Aquila, I-67100 L'Aquila and Ist. Naz. Fisica Materia (INFM), Italy. dellalongo@vaxaq
Pin
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Cortès
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Soldatov
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Alpert
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B
D000818:Animals; D001665:Binding Sites; D055592:Biophysical Phenomena; D001703:Biophysics; D006418:Heme / Q000737:chemistry*; D006736:Horses; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007501:Iron / Q000737:chemistry*; D009206:Myocardium / Q000737:chemistry; D009211:Myoglobin / Q000737:chemistry*; D011487:Protein Conformation; D013057:Spectrum Analysis; D013696:Temperature; D014907:Whales; D014965:X-Rays
D009211:Myoglobin; C017595:oxymyoglobin; D006418:Heme; D007501:Iron