Determination of collagen fibril structure and orientation in connective tissues by X-ray diffraction

Elastic scattering of X-rays can provide the following information on the f ibrous protein collagen: its molecular structure, the axial arrangement of rod-like collagen molecules in a fibril, the lateral arrangement of molecul es within a fibril, and the orientation of fibrils within a biological tiss ue. The first part of the paper reviews the principles involved in deducing this information. The second part describes a new computer program for mea suring the equatorial intensity distribution, that provides information on the lateral arrangement of molecules within a fibril, and the angular distr ibution of the equatorial peaks that provides information on the orientatio n of fibrils. Orientation of fibrils within a tissue is quantified by the o rientation distribution function, g(phi), which represents the probability of finding a fibril oriented between phi and phi+delta phi. The application of the program is illustrated by measurement of g(phi) for the collagen fi brils in demineralised cortical bone from cow tibia. (C) 1999 Elsevier Scie nce Ltd. All rights reserved.