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Second derivative fluorescence spectra of indole compounds
Suprabha Nayar1, Amrita Brahma, Chaitali Mukherjee
1Division of Protein Engineering, Indian Institute of Chemical Biology, Raja S.C. Mallick Road, Jadavpur, Calcutta-700032, India.
Journal of Biochemistry
|March 2, 2002
Summary
The study introduces a new method using the fluorescence ratio (R) of N-acetyl tryptophan amide (NATA) to assess protein structure. This R value, derived from second-derivative spectra, is sensitive to tryptophan
Area of Science:
- Biochemistry
- Biophysics
- Spectroscopy
Background:
- Tryptophan fluorescence is sensitive to its microenvironment.
- Existing methods for analyzing tryptophan fluorescence have limitations in quantifying subtle environmental changes.
Purpose of the Study:
- To develop a novel spectroscopic method for assessing the hydrophobic environment of tryptophan residues in proteins.
- To establish a new index, R, derived from second-derivative fluorescence spectra, for monitoring protein conformational changes.
Main Methods:
- Second-derivative fluorescence spectroscopy of N-acetyl tryptophan amide (NATA) and proteins.
- Measurement of the intensity ratio (R) of derivative fluorescence peaks at specific wavelengths.
- Correlation of R values with protein unfolding/refolding transitions induced by denaturants and proteolysis.
Main Results:
- The ratio R (358.5 nm / 340 nm) of NATA fluorescence is invariant to pH, temperature, salt concentration, and excitation wavelength but sensitive to solvent polarity.
- Derivative spectra of proteins resemble NATA, with low R values indicating buried tryptophans and higher R values indicating exposed tryptophans.
- R values accurately reflect protein unfolding and refolding transitions, correlating well with other biophysical parameters.
Conclusions:
- The R value is a sensitive and robust index for monitoring the hydrophobic environment of tryptophan residues in proteins.
- This method offers a more sensitive approach to studying protein structure and conformational dynamics compared to traditional fluorescence intensity or emission maximum measurements.