Shape of the carbon monoxide infrared absorption band of carboxyheme proteins as a probe of the protein anharmonicity

Abstract

Abstract. Theory of the CO infrared absorption band of carbonmonoxyheme proteins is developed using results of the theory of optical absorption bandshape of impurity center in crystal. It is shown that the bandshape is controlled by electrostatic interaction to the polar or/and charged heme surrounding. Analysis of the CO bands of different heme proteins brings us to conclusion, that the CO band is broadened by very slow (τ > 10 ps) motions of the heme surrounding and this motion most probably corresponds to the slow collective motion of the protein molecule. Therefore the second moment of the band must depend linearly on temperature at T > 25 K if the heme surrounding moves harmonically. The motion of the protein formed surrounding of the heme is arrested by the glassy protein environment. It is shown that Gaussian is the only possible symmetric shape of the CO band, if the heme surrounding moves harmonically. Deviation from this bandshape is a manifestation of anharmonic character of the surrounding motion. In general, CO infrared absorption band is shown to be an excellent probe of the dynamics of the heme surrounding.

Intercluster Redox Coupling Influences Protonation at the H-cluster in [FeFe] Hydrogenases

“…The maximum amplitudes of the F red H ox pdt and F ox H red pdt states were assumed to be the same as those of the F ox H ox pdt and F red H red pdt states, respectively. The peaks could be fitted very well with Gaussian functions, as has been demonstrated previously for IR peaks from other metal-bound CO ligands in proteins. − Negligible improvement in the fitting was achieved by using Voigtian functions (Figure S6), and the peak positions were unaffected. IR peaks from molecules in solution normally display Voigtian line shapes compared with Gaussian line shapes for solids due to free rotation in the former.…”

Mössbauer spectroscopy as a probe of electric field in heme pocket of deoxyheme proteins: theoretical approach

“…Comparison of the experimentally observed C-O vibrational frequency, ν(CO), and the dissociation rate constants of CO, NO and O2 of different Mb mutants with the calculated EF in the heme pocket showed [4] that the protein EF affects both the ν(CO) and the affinity of the heme for these diatomic ligands. A recent study of the CO complex of horseradish peroxidase showed that not only the position of the CO infrared band, but also its width is very revealing, providing specific information on the dynamics of the heme environment (see, for example [21][22][23][24]).…”