Effects of High‐Energy Electrons and Gamma Rays Directly on Protein Molecules

• Published in: Journal of pharmaceutical sciences Vol. 90; no. 10; pp. 1637 - 1646
• Main Author: Kempner, E.S.
• Format: Journal Article
• Language: English
• Published: New York Elsevier Inc 01.10.2001; John Wiley & Sons, Inc; Wiley; American Pharmaceutical Association
• Subjects: Biological and medical sciences; direct effects; Dose-Response Relationship, Radiation; Electrons; Enzymes - radiation effects; Freezing; Gamma Rays; General pharmacology; Humans; macromolecules; Mathematics; Medical sciences; Pharmacology. Drug treatments; Physicochemical properties. Structure-activity relationships; Poisson Distribution; Proteins - chemistry; Proteins - metabolism; Proteins - radiation effects; radiation; Radiation Tolerance; Radiation, Ionizing; Structure-Activity Relationship; target theory; macromolecules; target theory; radiation; direct effects; High energy radiation; Ionizing radiation; Stability; Ionization; Macromolecule; Physicochemical properties; Protein
• ISSN: 0022-3549; 1520-6017
• DOI: 10.1002/jps.1114

High‐energy electrons and gamma rays ionize molecules at random along their trajectories. In each event, chemical bonds are ruptured, releasing radiolytic products that diffuse away. A solution of macromolecules is mostly water whose principal radiation products are H+ and OH−. These can diffuse to and react with macromolecules; this indirect action of radiation is responsible for 99.9% of the damage to proteins. In frozen samples, the ionizations still occur randomly and water is still the principle molecular target, but diffusion of radiation products is limited to only a very small distance. At very low temperatures, essentially all the radiation damage to macromolecules is due to primary ionizations occurring directly in those molecules. Therefore, proteins in frozen solutions are only 10−3 to 10−4 as sensitive to radiation as in the liquid state. Every molecule that suffered a direct ionization is destroyed; the only surviving molecules are those that escaped ionization. The survival of frozen proteins after irradiation is a direct measure of the mass of the active structures and independent of the presence of other proteins. © 2001 Wiley‐Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:1637–1646, 2001