Effects of Ionizing Radiation on the Ultrastructure of Collagen Fibrils

The irradiation of collagen has been shown to lead to extensive changes in its physical properties (1, 2) despite little change in the chemical composition (3). This suggests that the changes are primarily due to disorganization of the secondary structure. These changes in physical properties may be reflected in the structure of collagen at the level of resolution of the electron microscope. Although considerable attention has been devoted to a study of collagen structure by means of the electron microscope, a positive electron-dense stain (4) reacting with specific groups has generally been employed (5). This technique would appear to be rather limited in detecting irradiation-induced changes, owing to their nonspecificity and the relatively small amount of chemical change occurring at the doses employed. A negative staining technique has recently been developed for collagen (6), however, and it is believed to demonstrate regions of different density within the fibril. The filamentous units revealed are thought to correspond to the collagen macromolecule. Irradiationinduced changes in fibril structure should therefore be readily detectable by this technique. This paper describes the results of investigations on the changes in collagen structure produced by irradiation, and an attempt is made to correlate the changes in the electron micrograph pattern with modification of physicochemical properties. METHODS Preparation of Materials