Conformational study of some milk proteins. Comparison of the results of electronic circular dichroism and vibrational circular dichroism

Solutions of proteins in D2O were measured using vibrational circular dichroism and electronic circular dichroism spectroscopy. The high sensitivity of vibrational circular dichroism spectra to conformational changes of proteins was demonstrated for the spectra of alpha-lactalbumin, beta-lactoglobulin and alpha-casein. Variations of the secondary structure were studied using the difference spectra obtained numerically from the spectra of solutions at different pH and different contents of alcohol. Enhancements of the alpha-helical fraction at pH 2 and the extended structure at pH 12 in alpha-lactalbumin were observed. The differences between the spectra of alpha-casein in the native state and in alcohol-containing solutions indicated a decrease in the beta-sheet fraction. Analogous variations of the solution pH and alcohol content caused negligible spectral changes in beta-lactoglobulin. This type of conformational study of proteins in solutions is extremely useful for electrochemical research of enzyme activities and electrochemical analysis of biomolecules.