Sentence:  There is some reason to think that thyroglobulin synthesis may proceed independently of iodination , for in certain transplantable tumours of the rat thyroid containing essentially no iodinated thyroglobulin , a <WSD>protein</WSD> that appears to be thyroglobulin has been observed in ultracentrifuge experiments ( Wolff , Robbins and Rall , 1959 ) . 
Meaning of the word marked with <WSD> tags:  any of a large group of nitrogenous organic compounds that are essential constituents of living cells; consist of polymers of amino acids; essential in the diet of animals for growth and for repair of tissues; can be obtained from meat and eggs and milk and legumes