ELECTRON SPIN RESONANCE IN THE STUDY 

 OF RADIATION DAMAGE* 



Walter Gordy 



Department of Physics, Duke University, Durham, North Carolina 



Abstract — It has been demonstrated by a Duke University microwave group that the electron 

 spin resonance of the resuUing unpaired electron can give specific information about the 

 radiation damage in proteins, nucleic acids, and many other biologically significant chemicals. 

 The structures of their electron resonances show that free radicals of various types are formed 

 from the different amino acids and simpler peptides by ionizing radiations. However, in 

 numerous proteins only two structural patterns are obtained, either separately or in com- 

 bination. One of these is like the common pattern obtained for cysteine, cystine, and gluta- 

 thione and is believed to arise from an unpaired electron (electron hole) on the protein sulfur. 

 The other pattern (obtained alone in proteins which have no sulfur) is a doublet characteristic 

 of the interaction of the electron spin with the spin of a single proton. The latter appears to 

 arise from an electron on a carbonyl oxygen interacting with a proton of the hydrogen bridge, 

 or possibly on a — CH — of the peptide chain which has lost an R side group. There is no 

 evidence that the ionizing radiation breaks the polypeptide backbone structure of the proteins. 

 The results seem to require that an electron hole or vacancy created at a given location in the 

 protein molecule can migrate to other locations where it has lower energy. 



I. INTRODUCTION 



Yesterday evening when coming over from the airport I discovered that I 

 was in the car with a biologist. After making this discovery, about half way 

 over, I asked my new acquaintance what it is that the biologists expect of the 

 physicists, what help — if any — we physicists can be to them. He told me 

 that we could give them better instruments. What they need as biologists, 

 he said, are newer and better instruments to see into things. He made no 

 mention of information or theory. I didn't ask him whether we were to bring 

 the instruments or just send them by mail. Nevertheless, I think that a physical 

 instrument which brings information out of biological things should be accepted 

 as a ticket of admission to a discussion of infonnation theory in biology, especi- 

 ally one held under the auspices of physicists ! 



The instrument which I offer as an admission ticket was not invented by 

 me. Electron magnetic resonance was discovered in 1945 by a Russian scientist, 

 Zavoisky (1). Nor can I claim to be the first to apply electron resonance to 

 the study of radiation damage. That, I believe, was first accomplished by 

 Hutchison (2), who in 1949 detected /'-center resonance in neutron-irradiated 

 alkali halides. Our group at Duke University, we are proud to say, was among 

 the first to show the applicability of electron magnetic resonance in the study 

 of biological substances, and the first, we think, to detect such resonances in 

 irradiated proteins. Combrisson and Uebersfeld (3), independently of our 



* This research was supported by the United States Air Force through the Air Force Office 

 of Scientific Research ARDC contract No. AF 18(600)-497. 



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