no The Iodine Complex of Thyreoglobulin 



mose it indicates either that the iodine group is altered in the 

 hydrolysis, or that the iodine-containing group when in simpler 

 combination or when separated, does not possess the full specific 

 thyroid activity. That the iodine-containing group when once 

 separated would not possess the full activity is not at all unlikely, 

 but we would be inclined to expect it to show some activity; 

 at least when given in amounts such as were employed by Strouse 

 and Voegtlin with iodotyrosine and by the author in the experi- 

 ments with tetra-iodohistidine anhydride and iodotryptophane. 

 The indications as to the presence of tyrosine and tryptophane in 

 iodothyrin are very favorable, both from the chemical studies on 

 iodothyrin and also from similar studies on iodine-free melanoi- 

 dins. 24 It is not likely that the iodine is split off and then later 

 added to the melanoidin fraction; it is more likely that it is already 

 present in the globulin in the melanoidin-forming groups and re- 

 mains in the original position in these groups, but that the groups 

 themselves are changed in regard to each other and thus the activ- 

 ity affected to some extent; a poly-iodo derivative may be changed 

 to a mono-iodo derivative and then may show decided differences 

 in physiological activities. If this were not the case we would 

 expect artificially iodized melanoidins to show a decided thyroid 

 activity. Furthermore, it is not likely that sufficient hydriodic 

 acid is split off in the early stages of the hydrolysis to yield as much 

 iodine as is contained in the melanoidin fraction. Finally, it is 

 not at all improbable that we here have to do with a specific 

 iodophore group just as in hemoglobin we have the chromophore 

 group containing the iron. The negative results with artificially 

 iodized proteins speak strongly in favor of this view. 



CONCLUSIONS. 



1. The full activity of thyroid tissue is contained in the thyreo- 

 globulin fraction when this activity is measured by the Hunt 

 method. 



2. The full activity per iodine unit is still present in the meta- 

 protein fraction from this globulin, although the iodine content 

 in the metaprotein fraction has been increased over threefold that 

 of the globulin itself. 



24 Samuely: Hofmeister's Beitr.age, ii, p. 355, 1902. 



