Reprinted from THE JOURNAL OF BIOLOGICAL CHEMISTRY. VOL. XIV, No. 2, 1913 



ON THE NATURE OF THE IODINE-CONTAINING 

 COMPLEX IN THYREOGLOBULIN. 



BY FRED C. KOCH. 



(From the Hull Laboratories of Biochemistry and Pharmacology, University 



of Chicago.} 



(Received for publication, January 27, 1913.) 



In this paper are given the results of an attempt to determine 

 the nature of the active complex in the iodine-containing active 

 principle of the thyroid gland. Although the nature of this group 

 was not determined, the quantitative physiological results here 

 reported serve to establish certain predicted and other unexpected 

 facts and to eliminate certain hitherto considered probabilities. 



The problem was taken up both by analytical and by synthetic 

 methods. In the former method the physiological activity and 

 iodine content of the dried thyroid tissue, the globulin therefrom 

 and various products of hydrolysis from this globulin were deter- 

 mined quantitatively. In the second method two iodized amino- 

 acid derivatives, not previously tested by quantitative methods, 

 were prepared synthetically and their physiological activity stud- 

 ied quantitatively. 



In thus tracing the active complex a number of important as- 

 sumptions were made. First, that the activity of unaltered thy- 

 roid tissue depends quantitatively on its iodine content. Second, 

 that the best method known for measuring this activity directly 

 and quantitatively is the Reid Hunt acetonitrile test. 1 Third, 

 that in case the iodine is present in the products of hydrolysis in 

 the same combination as in the globulin then, per unit of iodine, 

 these will still possess an activity comparable with the original 

 globulin. Fourth, that in case the iodine complex is an iodized 

 amino-acid and that in case this is decomposed in the process of 

 hydrolysis then the synthetic preparation of various iodized 

 amino-acids or derivatives thereof and the quantitative testing of 



1 This Journal, i, p. 33, 1905. 



THE JOURNAL OF BIOLOGICAL CHEMISTRY, VOL. XIV, NO. 2. 



