The limiting collagen microfibril. The minimum structure demonstrating native axial periodicity.
Collagen fibers were grown from solutions of acid-soluble or neutral salt-soluble collagen in 0.5 M acetic acid by rapid dialysis. The collagen was obtained under conditions where protease inhibitors were present at every stage of extraction and purification. Under the conditions used, length-wise but not lateral filament growth proceeded rapidly and gel-like networks were formed, Water readily exuded from the networks. The networks were stretched to fibrous form during drying. Small-angle X-ray diffraction showed the stretched fibrils to be highly ordered, showing up to 20 orders of the 670 A meridional periodicity. Intermediate- and wide-angle photographs show equatorial reflections at a spacing corresponding to approximately 12.5 A which is related to the intermolecular distance but none related to a microfibrillar packing at the 35-40 A level. Electron microscopy of the gel networks before stretching shows the presence of thin filaments with diameters predominantly in the 35-40 A range. No cross-striated fibrils are seen in electron micrographs of either stretched fibers or unstretched fibers. Thus, intermolecular packing in accord with the 670 A axial periodicity can take place within approximately 40 A diameter thin filaments. These correspond to the structures previously postulated to be collagen 'microfibrils'.
D000818:Animals; D003094:Collagen; D008854:Microscopy, Electron; D011487:Protein Conformation; D051381:Rats; D013710:Tendons; D014961:X-Ray Diffraction
D003094:Collagen