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 protein that <WSD>appears</WSD> to be thyroglobulin has been observed in ultracentrifuge experiments ( Wolff , Robbins and Rall , 1959 ) . 
Meaning of the word marked with <WSD> tags:  give a certain impression or have a certain outward aspect