Stained native collagen: interpretation of the small angle X-ray scattering and electron microscopic pictures in terms of the primary structure.

The average axial electron-density distribution of stained collagen fibers derived from X-ray small angle pattern, is shown to be substantially related to the projection of the polar amino acid residues onto the axis of the microfibril taking into consideration the staggering of neighbouring molecules. In order to arrive ultimately at a quantitative representation of the experimental data, an additional periodic fluctuation of the density in direction of the fibril axis is required. The necessity of this regular microphase structure for an understanding of known physical properties of collagen fibers will be indicated.