The parallel helices of the intermediate filaments of alpha-keratin

Recent Fourier transform infrared spectroscopy (FTIR) with attenuated total reflection technique (ATR) has been applied to alpha-keratin fibers (horse-hair) extended in water both at 21 and 95 degrees C. Infrared absorption bands in the Amide 1 region indicated that at extensions to 40-50% strain in water at 21 degrees C alpha-helices had completely disappeared and parallel beta-sheets were formed Appl. Spectrosc. 55 (2001) 552]. However, when the hair fibers were extended to the same strain at 95 degrees C in water the result was the formation of anti-parallel beta-sheets. These results suggest that the relatively more stable anti-parallel beta-state Polymer 10 (1969) 810] is only attained in extended alpha-keratin fibers at elevated temperatures and must result from major molecular rearrangement. It was concluded that the alpha-helices in the intermediate filaments (IFs) of alpha-keratin fibers must be parallel. This is in contrast to the previously accepted orientation of anti-parallel alpha-helices, based primarily on findings of X-ray diffraction studies of the structure of beta-keratin in highly extended fibers Polymer 10 (1969) 810; Keratins, IL: Thomas Springfield (1972); Nature 316 (1985) 767].