258 Walter Gordy 



Although our measurements were made in dry — reasonably dry — samples, 

 it seems likely that the same transfer of an electron hole to low-energy sites, 

 such as the side-chain sulfur, would take place in the proteins of living systems. 

 The better mobility of charges in the more fluid systems should only speed 

 up the recapture of an electron and hence the recovery of the system. Of course 

 the attack on the charged radicals such as — (S — S)+ — by molecules like H.2O 

 would also be speeded up in the living systems, but in the living systems the 

 electron recovery might well be the more rapid. Even if a break in the S — S 

 bond should occur, this might be less damaging and more easily healed than 

 a break in the polypeptide trunk line. 



We seem to be proposing here a self-protective mechanism which would 

 prevent almost any radiation damage whatever to proteins. This is not true 

 for several reasons, one of which is that not all proteins have — S — S — hnks 

 in their side chains. There are other traps for the 'hole' where bonds are 

 probably broken as postulated for silk, or for the sulfhydryl group, where 

 the hydrogen atom or proton is believed to be freed. A free hydrogen atom 

 could cause trouble in the living system, even though it could be temporarily 

 spared from the S — H group of the protein. Moreover, not all damage to proteins 

 in the hving systems is due to the direct ionization of the protein which we have 

 been discussing here. Much of the damage (30) is thought to be done by 

 radicals such as H, OH, and OOH produced by radiation in the inter-pene- 

 trating fluid, which later attack and damage the protein. These are the so-called 

 indirect effects. 



About the time of our initial experiment on the proteins, a very significant 

 experiment of an entirely different kind was in progress by Eldjarn, Pihl, and 

 Shapiro (31) which indicated that the indirect effects are probably not as 

 significant as had been previously thought, and that a high degree of protection 

 could be achieved by previously converting the — SH groups in proteins to 

 — S — S — links. Their experiments are of a chemical nature and employ 

 tagged sulfur (S^^) in cysteamine (NH2C2H4SH). I shall not attempt to give 

 the details of their experiments but merely to connect their results with ours. 

 The interdependence of the two apparently different types of results has been 

 pointed out in an interesting paper by Ehrenberg and Zimmer (32). Our 

 results indicate that any ionization of a protein which contains S — H groups 

 would always tend to dissociate the — SH group through the migration of the 

 'hole' or positive charge to the S. Because of the large cross-section of the 

 proteins there would be a large release of H atoms by this mechanism unless 

 there were many competing — S — ^S — links or other traps in the protein to 

 protect the — SH. The experiment of Eldjarn et al. would seem to 'protect' 

 the — SH group by first destroying it! By carrying the hydrogen away 

 peacefully in a harmless molecule they prevent its being released by the irradia- 

 tion as a damaging free radical. Later, after the upheaval is past, it can be 

 restored peacefully if needed. 



Our results, as well as those of Eldjarn et al., suggest that some agents may 

 exert their protective eff'ects by becoming temporarily attached through a 

 chemical bond to the protein or other thing which they protect. Cystine, 

 glutathione, or other agent which gives up electrons easily is needed for 

 protection against the damaging effects of positive holes. Cysteine, glutathione 



