Electron density distribution of dry avian tendon

The electron density profile along the unit cell of dry native collagen is determined. The method used is a modification of one that has been used successfully for wet native collagen. Uranyl acetate and phosphotungstic acid were used for isomorphous addition in phase determination and were located by electron microscopy. Structure factor magnitudes for dry collagen with and without the heavy metals were obtained from X-ray diffraction data. The first 9 orders were investigated. Standard Argand diagrams provided a unique solution for the phase of each. The resultant profile suggests that significant conformation changes occur in both the non-helical ends and the triple-helix portions of the molecules.