STRUCTURAL CHARACTERIZATION OF P-LACTOGLOBULIN IN SOLUTION USING 2-DIMENSIONAL FT MIDINFRARED AND FT NEAR-INFRARED CORRELATION SPECTROSCOPY

Two-dimensional (2D) FT-IR correlation analysis was applied to both th e mid-IR (MIR) and near-IR (NIR) regions to investigate changes in the secondary structures of beta-lactoglobulin in D2O (or H2O) solvent sy stems consisting of varying concentrations of bromoethanol, Mid-IR cor relation spectra indicate that the amide I bands corresponding to diff erent structures (i.e., alpha-helical structures at 1650 cm(-1), aggre gated beta-strands at 1620 cm(-1), and beta-sheet at 1636 cm(-1)) exhi bit apparently different spectral response towards varying concentrati ons of bromoethanol. We propose that the mechanism for the conversion of the beta-sheet into alpha-helix occurs in terms of two parallel pat hways, i.e., (1) beta-sheets --> aggregated beta-strands --> alpha-hel ix, and (2) beta-sheets --> alpha-helix, Although the amide B/amide II combination bands give no spectral features relating to the secondary structure, changes were found in the C-H combination bands that sugge st an interaction between the solvent and the protein.