Sentence:  The mechanism of action of these drugs has not been completely worked out , but certain of them appear to act by reducing the oxidised form of iodine before it can iodinate <WSD>thyroglobulin</WSD> ( Astwood , 1954 ) . 
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