Study on the redox state dependent gamma(CH) vibrational modes of the c-type heme.

Absorbance Fourier transform infrared (FTIR) spectra of model compounds for heme proteins such as protoporphyrin-IX, hemin, and hematin have been directly compared to the data of electrochemically induced FTIR difference spectra of small c-type proteins, i.e., microperoxidase-11, and cytochrome c. A band at 840-830 cm(-1) occurring in all studied samples dominated the spectra. The position of this vibrational mode depends on pH and the oxidation state, and could be assigned to the gamma(CH) mode of the porphyrin ring. Further features, such as the ring vibrations sensitive for the presence of iron and its oxidation state, are shown in the low-frequency infrared region between 750 and 650 cm(-1).