Organization of microfibrils in keratin fibers studied by X-ray scattering- Modelling using the paracrystal concept

Low-angle X-ray scattering patterns of hard alpha-keratin fibers have been studied for more than 50 years but a completely convincing modelling has ne ver been presented. The models which have been proposed so far are specific to the sample and cannot be adapted to others, mainly because they do not use a parametric analytical expression of the distribution function describ ing the relative positions of the microfibrils. Our new approach is based o n a paracrystal distribution function. In addition, a huge background origi nating from a non-ordered matrix is taken into account. Various hard alpha- keratins from different origins have been studied using our approach. From the rather good modellings obtained, it appears that the diameter of the mi crofibril is not origin dependent (7.4 nm) whereas the distances between mi crofibrils and their electron density profiles are. Hair microfibrils can b e reasonably approximated by a solid cylinder but a core and an outer ring are necessary for porcupine. Our method is of course not limited to keratin microfibrils; it can be used for modelling equatorial X-ray scattering pro files of all types of hexagonal fibrillar assemblies, which are in fact wid ely found in biological tissues. (C) 1998 Elsevier Science B.V. All rights reserved.