Structure of α-Keratin

Abstract

IN a recent publication, Fraser, MacRae and Miller1 have given a comprehensive interpretation of the X-ray diffraction photograph of α-keratin (porcupine quill tip) and, in particular, considered the quantitative aspects of the small-angle and large-angle equatorial scatter. This problem has also been discussed by Wilson2, whose approach differs in some important respects from that of Fraser et al., although based on a microfibril model of the same type. Wilson supposes that interference effects between protofibrils within a microfibril, as well as between different microfibrils, affect the X-ray intensity at small scattering angles, whereas Fraser et al. consider only the ‘between microfibril’ interference. According to them, the small-angle scatter can be ascribed solely to a difference in effective mean electron density between the microfibrils and their surrounding matrix, and for a given microfibril-matrix texture the intensity should be simply proportional to this difference. The evidence in favour of this idea is that when heavy metals, such as silver or osmium, are incorporated in the matrix material the main effect on the diffraction is to enhance the small-angle scatter, leaving the maxima of intensity at the same scattering angles as before.