Native and denatured Zn cytochrome c studied by fluorescence line narrowing spectroscopy.
BIOCHIMICA ET BIOPHYSICA ACTA 1993;
1161:149-60. [PMID:
8381668 DOI:
10.1016/0167-4838(93)90208-9]
[Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
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.
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