Mössbauer characterization of the tetraheme cytochrome c₃ from Desulfovibrio baculatus (DSM 1743): Spectral deconvolution of the heme components

Mössbauer spectroscopy was used to study the tetraheme cytochrome c₃ from Desulfovibrio baculatus (DSM 1743). Samples with different degrees of reduction were prepared using a redoxtitration technique. In the reduced cytochrome c₃, all four hemes are reduced and exhibit diamagnetic Mössbauer spectra typical for low‐spin ferrous hemes (S= 0). In the oxidized protein, the hemes are low‐spin ferric (S= 1/2) and exhibit overlapping magnetic Mössbauer spectra. A method of differential spectroscopy was applied to deconvolute the four overlapping heme spectra and a crystal‐field model was used for data analysis. Characteristic Mössbauer spectral components for each heme group are obtained. Hyperfine and crystal‐field parameters for all four hemes are determined from these deconvoluted spectra.