STRUCTURAL STUDY OF THE CALCIFYING COLLAGEN IN TURKEY LEG TENDONS

The calcified turkey leg tendon represents a simple bone-like tissue that is ideally suited to analysis by diffraction methods. In this paper we report some structural studies of the tendon collagen in the uncalcified, fully calcified and partially calcified states. The low-angle meridional X-ray pattern from the uncalcified tendon is very similar to that of the rat tail tendon, and the resulting one-dimensional structure of the collagen fibril exhibits no feature that could be related to its eventual calcification. The structure of the fully calcified tendon, as determined by a combination of X-ray and neutron diffraction analyses, shows that the mineral is associated with the collagen at the level of the hole or gap region. In the calcifying tendon, increases in the amplitudes of the first and second X-ray meridional reflections are correlated with an increase in the mineral content of the collagen. On the basis of simple models, it is shown that this change in the pattern can be explained by a nucleation mechanism of calcification. It is concluded that when collagen becomes calcified the mineral penetrates throughout the fibril and is crystalline in the hole region but amorphous between the collagen molecules. The mechanism of calcification and the mechanical implications of the fully calcified structure are also discussed. © 1979.