The absorption spectra of the proteins, egg albumin, lactalbumin, and gelatin were studied and compared with those of related amino acids and simple peptides; the effect of various solvents on these compounds was investigated. A region of selective absorption at about 280 mµ, common to proteins and to simple peptides, indicates that the seat of absorption is the peptide linkage which is the main bond in such compounds. This region coincides with that characteristic of tryptophane and tyrosine. The band consists of two components, whose separation in proteins and amino acid peptides is approximately 1200 wave numbers and in anilides about 850 wave numbers. The breaking of the peptide linkage is the cause of denaturation; the energy required is about 4.4 electron volts and varies with the solvent.
GLADYS A. ANSLOW and SALWA C. NASSAR, "The Absorption of Ultraviolet Energy by the Peptide Linkage," J. Opt. Soc. Am. 31, 118-122 (1941)