Native and denatured Zn cytochrome c studied by fluorescence line narrowing spectroscopy.
Fluorescence Line Narrowing (FLN) spectroscopy was employed to compare the environment around the porphyrin in folded and unfolded Zn-substituted cytochrome c (Zn cyt c). Parameters of the resolved spectra, including the inhomogeneous energy-distribution function, vibrational energy levels, and phonon coupling, were compared for guanidine-denatured Zn cyt c and native Zn cyt c. The spectra of denatured Zn cyt c showed increased broad background and decreased peak resolution when compared to the native protein, indicating that denaturation results in increased phonon coupling. The energy-distribution function for the unfolded protein was fitted to a single Gaussian centered at 17,230 cm-1 with a width of approx. 360 cm-1, which proved to be blue shifted and much wider than that for native Zn cyt c (approx. 65 cm-1). Vibrational frequencies of the ground-state for Zn cyt c were identified and shown to change upon denaturation. Temperature-dependence of the FLN spectra of native Zn cyt c was analyzed and found to have step-like broadening between 40 K and 50 K. Such discontinuous spectral broadening behavior suggests that a discrete conformational change occurs in the protein at these temperatures.
Logovinsky
V
V
Department of Biochemistry and Biophysics, School of Medicine, University of Pennsylvania, Philadelphia 19104.
Kaposi
A D
AD
Vanderkooi
J M
JM
D000818:Animals; D003574:Cytochrome c Group / Q000737:chemistry*; D006736:Horses; D011489:Protein Denaturation; D013050:Spectrometry, Fluorescence / Q000379:methods; D013696:Temperature; D015032:Zinc / Q000737:chemistry*
D003574:Cytochrome c Group; D015032:Zinc