Two very long periodicities in collagen.

A low-angle X-ray diffraction study of skin and breast-duct collagen, using synchrotron radiation, has disclosed an equatorial periodicity, common to all specimens, of about 350 nm. Tendons did not show any such periodicity, indicating that this phenomenon is restricted to two-dimensional distributions. In addition, shorter equatorial periodicities were also in evidence, which were in most instances different for different specimens, occurring in the range of 40 to 140 nm. Electron micrographs suggest the possibility that the first periodicity could be linked with blocks of the collagen molecule, which has a length of about 300 nm. The shorter periodicities give the tissue specific interfibrillar lateral packing of the individual collagen microfibrils.