Conformation changes of beta-lactoglobulin: an ATR infrared spectroscopic study of the effect of pH and ethanol.

Fourier transform infrared spectroscopy has been applied to investigate the secondary structural changes of beta-lactoglobulin in water/ethanol mixtures. The studies were carried out at two different pHs and at high protein concentrations. The spectra were recorded using an attenuated total reflection cell. The amide I band of beta-lactoglobulin in water reveals large amounts of intra extended beta-sheet structure. About 20% ethanol, beta-lactoglobulin unfolds and beta-strand formation is observed. alpha-Helices are built up by increasing the ethanol concentration up to 30%. In 50% ethanol, beta-lactoglobulin gels providing the apparent pH are neutral. The secondary structural changes of beta-lactoglobulin were observed on the similarity maps obtained by Principal Component Analysis.