Protein influence on the heme in cytochrome c: evidence from Raman difference spectroscopy.

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Abstract
Raman difference spectra were obtained for the cytochromes c of a number of species [Candida krusei, Rhodospirillum rubrum, baker''s yeast, horse, tuna, pigeon, dog, spider monkey, human, cow and turtle] by simultaneous data acquisition from 2 samples. Frequency differences as small as 0.1 cm-1 can be measured reproducibly by the technique. In comparisons between cytochromes c isolated from 2 different species, the frequency differences in the heme vibrational modes range from 0-6 cm-1. The vibrational frequencies of the heme are sensitive to the electronic charge density on the porphyrin macrocycle. The frequency differences are interpreted in terms of the influence of the heme-packed aromatic and highly electronegative amino acid side chains on the .pi.* charge density and distribution on the heme. Such a control of the electronic properties of the heme by the protein may be important for the function of cytochrome c.