Abstract: Fourier transform infrared spectroscopy is increasingly becoming an important method for quantitatively determining the secondary structure of proteins. Amide Ⅰ band(1 600-1 700cm^-1) and amide Ⅲ (1 220-1 330cm^-1) are two main bands for this purposes. Amide Ⅲ was neglected because of its relatively weak in signals, but there is not interference from water and water vapor vibration bands and it is more sensitive to the changes of protein secondary structure. In this paper, proteins BSA and RNase A were denatured by methanol. The component bands of secondary structure in amide Ⅲ were assigned by combining the quantitative results of amide Ⅰ band. α-Helix 1 330-1 290cm^-1; β-turn 1 295-1 265cm^-1; Random coil 1 270-1 245cm^-1 and β-sheet 1 250-1 220cm^-1. The overlapping area between the neighboring bands of different structures, such as 1 290-1 295cm^-1, 1 265-1 270cm^-1, 1 245-1 250cm^-1, can be determined according to quantitative results of amide Ⅰ band. By using above assignments, the quantitative analysis results of the proteins in which the secondary structures have been known were consistent with that of X-ray data and amide Ⅰ band.

Key words: FTIR, Amide Ⅲ band, Secondary structure of proteins, Solvent denaturation