[13] Resolution-enhanced fourier transform infrared spectroscopy of enzymes

This chapter describes the basic principles, techniques, and applications of resolution-enhanced Fourier transform infrared spectroscopy. Infrared spectroscopy constitutes one of the oldest methods for studying the secondary structure of polypeptides and proteins. Polypeptides and proteins exhibit a total of nine characteristic absorption bands in the infrared region. These are usually termed the amide A, B, and amide I-VII bands. The amide I (∼1630-1690 cm-1) band is the most useful for protein structure studies by infrared spectroscopy. The use of Fourier transform infrared spectroscopy (FTIR) has led to major improvements in this regard. In principle, FTIR provides several advantages over conventional dispersive techniques: higher (1) resolution, (2) sensitivity, (3) signal-to-noise ratio (S/N), and (4) frequency accuracy. Any one of the first three advantages can be emphasized at the expense of the other two. For protein structure studies, high sensitivity makes it possible to acquire usable infrared spectra of aqueous solutions; such spectra are always notoriously difficult to obtain.