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Structural studies of cytochrome-c-554 from chloroflexus-aurantiacus by resonance Raman-spectroscopic techniques
Citation key ISI:A1991GN76200006
Author Heibel, G and Griebenow, K and Hildebrandt, P
Pages 196-202
Year 1991
ISSN 0006-3002
Journal Biochimica et biophysica acta
Volume 1060
Number 2
Month OCT 18
Abstract The four-heme cytochrome c-554 of Chloroflexus aurantiacus was studied by resonance Raman and surface-enhanced resonance Raman spectroscopy. The resonance Raman spectra show the characteristic vibrational signature of c-type hemes as demonstrated by a comparison with those of horse-heart cytochrome c, which were obtained under identical conditions. Spectral differences between both cytochromes can be related to the porphyrin geometry and the interactions of the heme with the immediate protein environment. Asymmetry of bands of cytochrome c-554 in all spectral regions provides support for conformational heterogeneity among the four hemes. The core-size-sensitive marker bands are interpreted in terms of a slight core contraction of the tetrapyrrole macrocycle in the six-coordinated low-spin states with respect to horse-heart cytochrome c. Shoulders on the low-frequency side of these modes indicate that at least one of the cytochrome c-554 hemes partially exists in a five-coordinated high-spin configuration. The analysis of the low frequency region provides evidence that some of the hemes are located in a more open and flexible protein pocket than in cytochrome c, accounting for the low-lying redox potentials. These structural data are complemented by the surface-enhanced resonance Raman results of cytochrome c-554 adsorbed on colloidal silver. These spectra reveal a significantly larger fraction of the five-coordinated high-spin configuration than in the case of cytochrome c. This can be attributed to a higher susceptibility to conformational distortions of these heme pockets upon electrostatic interactions with the charged silver surface.
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