THE ABSENCE OF RADIATION-INDUCED 

 DISULFIDE INTERCHANGES* 



Arthur L. Koch f 



Division of Biological and Medical Research, Argowie National Laboratory, 



Lenwnt, Illinois, 



and 



Department of Biochemistry, University of Florida, 



Gainesville, Florida 



Abstract — Mixtures of cystine and its 6/i-dinitrophenyl derivative were: (a) irradiated as dry 

 films, (b) treated in aqueous solution with Fenton's reagent, and (c) irradiated in aqueous 

 solution. In none of these cases could any of the interchange product, mono-dinitrophenyl 

 cystine, be detected. It is therefore inferred that disulfide interchange is not a primary cause 

 of protein denaturation or enzyme inactivation by ionizing radiations. 



As a consequence of treatment of proteins and protein solutions with large 

 doses of ionizing radiations, denaturation, as assessed by decreased solubility 

 at the isoelectric point, frequently occurs (1). The involvement of sulfur linkages 

 in these solubihty changes as well as in the concomitant loss of biological 

 activity has been frequently suggested. The importance of the oxidation of 

 existing thiol groups to disulfides is well documented (2), but another possi- 

 bility is that polymerization results from disulfide interchange, in a manner 

 similar to that postulated by Huggins, Tapley, and Jensen (3) to account 

 for gel formation in the presence of urea. In their case the initiator of the chain 

 reaction was assumed to be a sulfhydryl group exposed by the unfolding of 

 the protein. This unfolding results from the breaking of intramolecular hydro- 

 gen bonds by the urea. One could, however, conceive of chain reactions 

 initiated by the free radicals produced by ionizing radiations. For example, 

 hydroxyl radicals produced by the action of the radiation on water could 

 react to produce a sulfenic acid and a sulfide radical, which could then react 

 further: 



OH + /?iSS/?.3 > 7?iS0H + S/?2 



Si?2 -r /?3SS/?4 >RS^R^ + S/?3 . 



Such a mechanism appears attractive in view of the properties of sulfur 

 compounds as presented by Calvin (4, 5). Further reactions of /^^SOH could 

 also lead to polymerization as a consequence of dismutation to the sulfide 

 and sulfinic acid. 



In order to investigate these possibilities, a model system was studied. 

 The system chosen was that utilized by Ryle and Sanger (6). These authors 



* This work performed under the auspices of the U.S. Atomic Energy Commission. 

 t Present address: Department of Biochemistry, University of Florida, Gainesville, 

 Florida. 



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