The α-β Transformation in Keratin

Abstract

THE possibility of obtaining from X-ray diffraction results a quantitative estimate of the course of the α-β transformation as a keratin specimen is stretched is so important that attempts such as that of Bendit¹ are to be welcomed. I feel, however, that it is impossible to say the same about the proposal recently put forward by V. D. Gupta², who measures for specimens at various extensions the value of an index which he wishes to take as a measure of what he calls the “degree of order”. So far as can be gathered from his somewhat ambiguous phraseology, the quantities I_m and I_e are the intensities of the meridional and equatorial diffraction spots, the former the group of reflexions with spacings near 5.1 A., and the latter the reflexions with spacings near 10 A. (common to the α- and β-photographs) and near 4.65 A. (characteristic of the β-photograph). If this interpretation of Gupta's intentions is correct, then changes in Ω are indications not so much of changes in the degree of order (whatever this might mean) as of changes in the β : α ratio. His conclusion that during stretching there is an initial rapid rise in the degree of order, with little further change at extensions greater than 40 per cent, should therefore be replaced by the almost trivial result (it was not so trivial 30 years ago) that the X-ray photograph at 40 per cent extension is more like that at 70 per cent extension than it is like that of unstretched fibres.