ELECTRONIC STRUCTURE OF BIOMOLECULES

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Abstract
The application of Mössbauer spectroscopy to the investigation of biomolecules is discussed for heme proteins. All heme proteins have basically the same active center, namely heme. The heme iron is usually either ferric or ferrous ; in either oxidation state both high-spin and low-spin configurations can occur. The low temperature Mössbauer spectra can be described by a spin Hamiltonian of the form ℋ = S.[MATH].S + βS.[MATH].H + S.[MATH].I + ℋQ – gn βn H.I. In low symmetries, which nature seems to prefer in biomolecules, the spin Hamiltonian will have a large number of unknown coefficients and the evaluation of the spectra is a formidable task. The Mössbauer spectra typical for the various charge and spin states of the heme iron are discussed ; cytochrome P450, chloroperoxidase and horseradish peroxidase are used as examples. For ferric heme proteins Epr results can be used to significantly facilitate the analysis of the Mössbauer spectra. For high-spin ferrous proteins Mössbauer measurements in strong applied fields are particularly useful ; such measurements on reduced cytochrome P450 are discussed in detail. In addition, Mössbauer emission experiments on 57Co substituted hemes are presented ; this type of spectroscopy provides a means of studying heme model compounds which cannot be prepared chemically

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