REDOX-DEPENDENT CONFORMATIONAL-CHANGES ARE COMMON STRUCTURAL FEATURESOF CYTOCHROME-C FROM VARIOUS SPECIES

Discrepant results from X-ray crystallographic and physicochemical stu dies on the conformations of the two redox states of cytochrome c rais e important questions about the nature of redox-dependent conformation al changes and whether differences are a common structural features of various cytochrome c species. Comparative studies of cytochrome c fro m 10 species (horse, cow, sheep, pig, dog, rabbit, chicken, pigeon, tu na, and baker's yeast) in aqueous solutions were carried out using Fou rier transform infrared (FT-IR) spectroscopy, The second-derivative an alysis revealed similar conformational changes in all 10 species upon reduction of the heme iron regardless of the differences in the amino acid sequences, The redox-dependent changes involve the amide I region s ascribed to extended beta-structure, beta-turn, and alpha-helix stru ctures. Three species (cow, sheep, and pig) with identical amino acid sequences displayed nearly identical infrared spectra for the oxidized and reduced states, which rules out the possible contribution of expe rimental error, These results show unequivocally that redox-dependent conformational changes are common structural feature of various cytoch rome c species and demonstrate the usefulness of FT-IR spectroscopy as a quick and inexpensive tool in comparative studies of functionally r elated conformational changes of proteins. (C) 1997 Academic Press.