Macromolecular structure and organization of alpha keratin

Abstract

The small-angle equatorial X-ray scattering of alpha keratin (African porcupine quill) was studied using a direct type of analysis, which allows the separation of the intermicro-fibrillar interference effects from those of the intramicrofibrillar scattering without the use of prior assumptions. X-ray data were obtained from 470–21 Å; their analysis by the above method resulted in a z -axis projection of the microfibrillar electron density, which extends over a diameter of 80 Å and has a core region surrounded by a peak located at a radius of 28 Å. The macromolecular organization of the 80-Å-diameter microfibrils was found to be an arc-like layer type of aggregation and not a pseudohexagonal packing. When the specimen was subjected to silver staining the aggregation of the microfibrils did not change except for a slight contraction. The z -axis projection of the stained microfibril, however, was significantly different. The silver appears to build up slightly around the outer periphery of the microfibril, stains the peripheral region very little, deposits on the inside of the peripheral region, and outlines the core area.