Sentence:  It has been suggested that the plasma thyroxine binding proteins , which have an extremely high affinity for thyroxine , compete with thyroglobulin for <WSD>thyroxine</WSD> ( Ingbar and Freinkel , 1957 ) . 
Meaning of the word marked with <WSD> tags:  hormone produced by the thyroid glands to regulate metabolism by controlling the rate of oxidation in cells