1
|
Abstract
One of the outstanding properties of collagen fibrils is an axial periodicity of about 640 Å and associated fine structure which can be observed directly in the electron microscope and also may be deduced from observation of low-angle X-ray diffraction. This paper gives first an account of measurements of density fluctuations along the fibril axis for unstained, unshadowed fibrils for one mammalian collagen, rat-tail tendon, and one avian collagen, fowl-neck tendon. The main and subsequent part of the paper shows how the density functions derived from electron micrographs obtained under specified conditions may be used to calculate the intensities of low-angle X-ray diffraction. Complications arise from the fact—of considerable biological interest—that for any one material a wide range of fine structure exists. For this reason it has been necessary to introduce a modulating function to represent the behaviour of a system of fibrils with differing density functions. The calculated structure amplitudes are compared with those measured from low-angle X-ray photographs of dry fibres. Good agreement between the two sets of results is found for rat-tail tendon and fair agreement for fowl-neck tendon. The agreement for fowl-neck tendon is improved by the application of a more general modulating function.
Collapse
|