A Study of the Amide III Band by FT-IR Spectrometry of the Secondary Structure of Albumin, Myoglobin, and γ-Globulin

Abstract

FT-IR spectrometry was applied to the identification of the secondary structure species of a living protein. The spectra of native myoglobin and albumin were obtained with methods using either KBr pellet or film formed on a KBr window from an aqueous solution. Pellet preparation of myoglobin and albumin caused the structure to change from α-helix to β-structure. The conformational changes that arise from heat denaturation of myoglobin, albumin, and γ-globulin were observed by the changes in the amide I, II, and III bands. The bands of the 1300, 1260, and 1235 cm⁻¹ regions were respectively assigned to α-helix, disordered, and β-sheet structures. These band positions were substantiated by the spectra of β-lactoglobulin and α-casein. α-Helix structure probably changes to β-structure in the presence of alkali halide, and changes to disordered structure with heat denaturation in phosphate buffer solution. The secondary structure of a protein is further identified by use of the information obtained from the amide I, II, and III bands; the amide III band is especially important. Furthermore, it may be possible to characterize the species of secondary structures of proteins adsorbed on material surfaces.