Modelling the surface lattice of alpha-keratin filaments.

A recently-proposed model for the distribution of scattering material on the surface lattice of alpha-keratin intermediate filaments in dry porcupine quill is examined in detail. It is shown that, while retaining the basic form of the model (namely a dislocated helix with finite lattice spacing of 198.2 A), alternative meridonal distributions of scattering material within the finite lattice unit cell can be obtained which are consistent with the low-angle meridional X-ray pattern. The Gaussian shape function used to demonstrate the finite lattice in the model is questioned. The meridional diffraction pattern from hydrated porcupine quill is also examined and, apart from the intense fifth order reflection, can be modelled by distortion of the dry species scattering material distribution.