Raman spectroscopic study of mechanically deformed poly-L-alanine
Article first published online: 1 FEB 2004
Copyright © 1974 John Wiley & Sons, Inc.
Volume 13, Issue 3, pages 455–474, March 1974
How to Cite
Frushour, B. G. and Koenig, J. L. (1974), Raman spectroscopic study of mechanically deformed poly-L-alanine. Biopolymers, 13: 455–474. doi: 10.1002/bip.1974.360130303
- Issue published online: 1 FEB 2004
- Article first published online: 1 FEB 2004
- Manuscript Revised: 26 NOV 1973
- Manuscript Received: 18 MAY 1973
Raman spectroscopy has been used in investigating the conformational transitions of poly-L-alanine (PLA) induced by mechanical deformation. We see evidence of the alpha-helical, antiparallel beta-sheet, and a disordered conformation in PLA. The disordered conformation has not been discussed in previous infrared and X-ray diffraction investigations and may have local order similar to the left-handed 31 poly glycine helix. The amide III mode in the Raman spectrum of PLA is more sensitive than the amide I and II modes to changes in secondary structure of the polypeptide chain. Several lines below 1200 cm−1 are conformationally sensitive and may generally be useful in the analysis of Raman spectra of proteins. A line at 909 cm−1 decreases in intensity after deformation of PLA. In general only weak scattering is observed around 900 cm−1 in the Raman spectra of antiparallel beta-sheet polypeptides.
The Raman spectra of the amide N–H deuterated PLA and poly-L-leucine (PLL) in the alpha-helical conformation and poly-L-valine (PLV) in the beta-sheet conformation are presented. Splitting is observed in the amide III mode of PLV and the components of this mode are assigned. The Raman spectrum of an alpha-helical random copolymer of L-leucine and L-glutamic acid is shown to be consistent with the spectra of other alphahelical polypeptides.