PubMed · 13989385
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E SMITH, M A EVERETT. 1962. Keratinization: A review.. https://pubmed.ncbi.nlm.nih.gov/13989385/
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Considerable physical evidence has been accumulated in support of the polarity of alpha-keratin fibres and is summarised here. Dielectric loss and dielectric dipole movement in dry intact fibres as they undergo thermal transition above 200 degrees C show alpha-keratin to be a polar structure. X-ray diffraction has shown that this transition corresponds to the randomisation of the organised alpha-helical structure resulting in the loss of polarity of the fibre. The piezoelectric properties of alpha-keratin can only be explained if its alpha-helical dipoles in the ordered structure alpha-keratin are synergistically aligned in the axial direction. If the alpha-helical units of the IFs of alpha-keratin fibre were in an anti-parallel conformation then dry alpha-keratin would show no polarity. FTIR measurements on alpha-keratin fibres extended in water at 21 and 95 degrees C explain the formation of anti-parallel beta-structures when fibres are extended in steam. Contrary to in vitro experimental data there is clear evidence that native alpha-keratin fibres are polar structures with the alpha-helices aligned in a parallel conformation.
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Quantitative measurements of the intensity of the meridional reflections in the X-ray-diffraction pattern of alpha-keratin are shown to be consistent with a microfibril structure in which a surface lattice with an axially projected period around 200 A is subject to a periodic interruption with an axially projected period of 470 A. Taken in conjunction with recent evidence on the chemical structure of alpha-keratin and other intermediate filaments this finding enables an elaboration to be made of a model proposed earlier by RDB Fraser, TP MacRae, & E Suzuki (J. Mol. Biol. 108, 435-452, 1976) for the alpha-helical framework of the microfibril. The disposition and connectivity of the helical segments suggested here provides a straightforward explanation of a number of recent physicochemical and electron-microscopical observations on intermediate filaments and provides a starting point for the development of models for the framework of other intermediate filaments.