Sentence:  A study of their activity on <WSD>thyroglobulin</WSD> has shown that thyroxine is not preferentially released and that the degradation proceeds stepwise with the formation of macromolecular intermediates ( Alpers , Petermann and Rall , 1956 ) . 
Meaning of the word marked with <WSD> tags:  an iodine containing protein that is obtained from the thyroid gland and exhibits the general properties of the globulins