1) Target analysis of the inactivation of biological activity by ionizing radiation was applied to three major problems: a) the binding sites for high density lipoproteins in different tissues; the binding of GTP by p21 ras proteins; and c) the infectious agent for scrapie. 2) Major reviews of previous radiation studies of enzymes and of membrane-associated functions were completed. 3) Work was completed on a general theoretical description of the effects of ionizing radiation which are unique to macromolecules. Objectives: 1) An understanding of the nature of active structures in vivo which are involved in biochemical processes, principally by means of the technique of inactivation by ionizing radiation. 2) Detailed knowledge of the molecular damage caused by ionizing radiation and of the mechanisms of the transfer of radiation energy throughout these structures. Methods: 1) General biochemical techniques including enzyme reactions, fluorescence, and gel electrophoresis. 2) Ionizing radiation, usually high energy electrons from a linear accelerator, to expose samples under carefully controlled conditions.