27] Circular dichroism and optical rotatory dispersion of proteins and polypeptides

Abstract

Publisher Summary This chapter discusses the methodology of circular dichroism (CD) and optical rotatory dispersion (ORD) data gathering and analysis in the rapidly changing field of protein structure, making use of synthetic polypeptide studies when necessary. ORD is the measurement, as a function of wavelength, of a molecule's ability to rotate the plane of linearly polarized light. CD is similar data evaluating the molecule's unequal absorption of right- and left-handed circularly polarized light. CD and ORD can yield useful estimates of protein secondary structure. Although all the amino acids except glycine contain at least one asymmetric carbon atom, most amino acids display only small ORD and CD bands. It is the conformation of the protein—that is, the asymmetric and periodic arrangement of peptide units in space, which gives rise to their characteristic ORD and CD spectra. In recent years, X-ray diffraction analysis has lead to the complete mapping of the peptide backbone and side-chain positions of lysozyme, several other enzymes, and quite a few other proteins in the solid state.