, Volume 36, Issue 1, pp 67-76

Mössbauer and molecular orbital study of the myoglobin-CO complex

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Experimental Mössbauer spectra of the Fe57-enriched CO complex of sperm whale myoglobin (MbCO) at T= 4.2 K with and without applied magnetic field (H⊥γ) were measured to derive the sign of the electric field gradient (EFG), the quadrupole splitting ΔE Q, and the isomer shift δ of the heme iron. We find a positive EFG, δE Q = 0.363 mm/sec, and δ + 0.266 mm/sec. Molecular orbital calculations were carried out to obtain theoretical estimates of EFG and ΔE Q for several steric arrangements of the CO ligand relative to the heme group. Our results are most consistent with the conclusion that the iron is situated in the heme plane, and that a bent geometry with a Fe-C-O angle of about 135 ° is more favorable than a more symmetric structure with a linear Fe-C-O geometry.

Supported in part by Stiftung Volkswagenwerk, in part by U.S. National Science Foundation GP-31373X, in part by an award from the Biomedical Sciences Support Grant at the University of Utah (U.S. Public Health Service Grant RR 07092), and in part by the European Molecular Biology Organization.