Functionally relevant electric-field induced perturbations of the prosthetic group of yeast ferrocytochrome c mutants obtained from a vibronic analysis of low-temperature absorption spectra.

We have measured the low temperature (T = 20 K) absorption spectra of the N52A, N52V, N52I, Y67F, and N52AY67F mutants of ferrous Saccharomyces cerevisiae (baker's yeast) cytochrome c. All the bands in the Q0- and Q(v)-band region are split, and the intensity distributions among the split bands are highly asymmetric. The spectra were analyzed by a decomposition into Voigtian profiles. The spectral parameters thus obtained were further analyzed in terms of the vibronic coupling model of Schweitzer-Stenner and Bigman (Schweitzer-Stenner, R.; Bigman, D. J. Phys. Chem. B 2001, 7064-7073) to identify parameters related to electronic and vibronic perturbations of the heme macrocycle. We report th…