Protein structure by Fourier transform infrared spectroscopy: Second derivative spectra

Second derivative Fourier transform infrared spectra of the proteins ribonuclease A, hemoglobin, and β-lactoglobulin A (native and denatured) have been obtained in deuterium oxide solution from 1350 to 1800 cm−1. The relationship of the original spectra to their second derivatives is briefly discussed. In the second derivative spectra, clearly resolved peaks are observed which can be associated with the α-helix, β-strands, and turns. No protein spectra with such resolution have heretofore been reported. Tentative assignments are proposed, and the observed peaks are related to the secondary structure of the proteins studied. The data appear to present the first direct spectroscopic evidence of turns in a native protein.