Amide III frequencies for Ala-X peptides depend on the X amino acid size.
Raman spectra of series of aqueous solutions of peptides containing two amino acids, glycine-X, alanine-X, and serine-X, where X is an uncharged amino acid, show that the amide III band shifts systematically to lower frequencies as the side chain of the X amino acid becomes larger. The range of this shift is about 20 cm-1, starting at 1275 cm-1 for alanine-glycine and moving to 1251 cm-1 for alanine-tryptophan, with a correlation coefficient of 0.93 with the mass of the X amino acid side chain for 10 peptides. The amide I frequencies remain constant as the X amino acid is changed. This shift may result from a change in the average conformational preference of the peptide, a change in vibrational coupling of the amide III modes with the X amino acid side chain, a change in molecular force constants, or a combination of these. These results present a test for computational methods.
Weaver
J L
JL
Department of Biochemistry, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814-4799.
Williams
R W
RW
D000409:Alanine / Q000737:chemistry; D000577:Amides / Q000737:chemistry; D000596:Amino Acids / Q000737:chemistry; D015394:Molecular Structure; D010455:Peptides / Q000737:chemistry*; D013059:Spectrum Analysis, Raman
D000577:Amides; D000596:Amino Acids; D010455:Peptides; D000409:Alanine