The Raman spectra of collagen, gelatin, and elastin are presented. The Raman lines in the latter two spectra are assigned by deuterating the amide N-H groups in gelatin and by studying the superposition spectra of the constituent amino acids. Two lines appear at 1271 and 1248 cm−1 in the spectra of collagen and gelatin that can be assigned to the amide III mode. Possibly, the appearance of two amide III lines is related to the biphasic nature of the tropocollagen molecule, i.e., proline-rich (nonpolar) and proline-poor (polar) regions distributed along the chain. The melting, or collagen-to-gelatin transition, in water-soluble calf skin collagen is studied and the 1248-cm−1 amide III line is assigned to the 31 helical regions of the tropocollagen molecule.

Elastin is thought to be mostly random and the Raman spectrum confirms this assertion. Strong amide I and III lines appear at 1668 and 1254 cm−1, respectively, and only weak scattering is observed at 938 cm−1. These features have been shown to be characteristic of the disordered conformation in proteins.