Synopsis
The Raman spectra of three globular proteins, beef pancreas chymotrypsinogen A, beef pancreas ribonuclease, and hen egg white ovalbumin have been obtained in the solid state and aqueous solution. X-ray diffraction and circular dichroism evidence have indicated that these proteins have a low a-helical content and a large fraction of the residues in the unordered and &sheet conformation. The frequencies and intensities of the amide I and amide I11 lines are consistent with assignments based on the Raman spectra of polypeptides. The intense amide I11 lines observed in all the spect.ra would be expected for proteins with a low fraction of the residues in the a-helical conformation. Several spectra changes occur upon dissolution of the proteins in water and may be associated with further hydration of the proteins. The spectrum of thermally denatured chymotrypsinogen is presented. A 3 cm-1 decrease in the frequency of the amide I line of the protein dissolved in DzO upon heating was observed. This observation is consistent with a denaturation mechanism allowing only slight changes in the secondary structure but an increase in solvent penetration upon going from the native to t.he reversibly denatured state.