THE CONTRIBUTION OF THE α-HELICAL CONFIGURATION TO THE OPTICAL ROTATION OF POLYPEPTIDES AND PROTEINS

Abstract

The evidence showing that L-polypep-tides can exist in solution as [alpha]-helices having a single screw sense, probably right-handed, is reviewed. It is then shown that the rotatory properties of such a helix devoid of the effects of asymmetric centers can be determined from properly prepared polypeptides. These polypeptides were made by using preformed L-polypeptides having the desired screw sense to initiate the polymerization of mixtures of D-and L-anhydrides. From rotatory dispersion measurements on these it is possible to show that the helical configuration is responsible for the effective residue rotation. Now that the rotatory dispersion due to the helical configuration is available, it can be used in conjunction with the rotatory dispersion of completely helical L-polypeptides or proteins to provide the rotatory dispersion of the residues (asymmetric centers) as they exist in the helix. This should be particularly useful in the quantitative study of protein structure and denaturation.