Structure of Collagen Fibrils
Axially, the molecules — roughly 300nm long and 1.0nm in diameter — are related by staggers of integral multiples of approximately 67nm; call this distance D. The idea in essence originated with Gross and his colleagues (Schmitt et al 1955; Gross 1956) but is customarily associated with Hodge and Petruska (1963) who formulated it rather precisely. It explains both the appearance of fibrils under the electron microscope and the meridional X-ray diffraction patterns obtained from different collagens.
In general, molecules are arranged laterally in an irregular fashion. The near-equatorial X-ray diffraction pattern suggests a structure in an equatorial projection reminiscent of a two dimensional simple liquid (Woodhead-Galloway and Machin 1976). This feature appears to be common to collagen fibrils from all sources.
In stretched native rat tail tendon the diffuse near-equatorial X-ray intensity is supplemented by a complicated pattern of discrete reflections, suggesting a molecular arrangement in some parts of the fibril that is crystalline or nearly so This pattern has been most compellingly interpreted (Hulmes and Miller 1979) as an approximately (quasi) hexagonal packing of molecules, tilted and sheared with respect to the fibril axis.
KeywordsCollagen Fibril Molecular Packing Molecular Arrangement Intermolecular Spacing Radial Separation
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