286 Arthur L. Koch 



amounts of the reactants were still present. In this experiment the dose was 

 delivered in a one-hour period. During this time the effect of the spontaneous 

 interchange catalyzed by thiols produced by hydrolysis of the disulfides is small 

 (6). In the presence of versene, which prevents metal-catalyzed oxidation 

 by molecular oxygen, the interchange is greater because of greater persistence 

 of thiol. For this reason, controls were included containing thiol binding 

 reagents which completely block thiol catalyzed interchanges. 



These preliminary experiments indicate that interchange of disulfide bonds 

 is not a prominent feature of radiation-induced denaturation. Further work 

 will be required to assess the role of disulfide linkages in secondary aspects 

 of denaturation. In addition, further work should be carried out using a 

 disulfide interchange indicator that is not itself influenced by irradiation in 

 aqueous solution and thus affords a more sensitive assay for interchange in 

 aqueous media. 



Acknowledgement — The author acknowledges with gratitude the continued 

 interest and valuable advice of his colleagues Howard S. Ducoff, George A. 

 Sacher, and Antreen Pfau. 



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