Infrared Spectra and Protein Conformations in Aqueous Solutions

Abstract

Abstract Infrared absorption spectra of poly-l-lysine, poly-l-glutamic acid, β-lactoglobulin, myoglobin, and αs-casein in the region of absorption of the amide I band have been observed in H2O solution, D2O solution, and in the solid state. The results indicate that characteristic frequencies exhibited by specific conformations of the investigated synthetic polypeptides are not transferable to corresponding conformations of globular proteins. The frequencies obtained for different conformations of globular proteins in H2O and D2O solution are internally consistent, in general agreement with corresponding values of fibrous proteins and with the limited data available in the literature concerning deuterated proteins in D2O solution. Dissolution in aqueous environment by itself does not noticeably alter the amide I frequencies. A tentative set of characteristic frequencies and interaction constants is obtained for the amide I' modes of N-deuterated proteins. These modes are easily observed in D2O solution and show sufficient variations in frequency to permit a distinction between the α-helical, the antiparallel-chain pleated sheet, and the solvated random configurations of globular proteins.