STUDIES ON AN IODINATED PROTEIN IN THE SERUM OF SUBJECTS WITH CANCER OF THE THYROID*†

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Abstract
An iodinated substance (compound X) found in the blood of certain patients with cancer of the thyroid appears to be homogeneous upon ultracentrifugation, and is similar in all cases studied. Its sedimenta- tion constant is S20, w=4.2 - 4.3. Most analytical procedures do not separate compound X from the albumin fraction of the serum. However, compound X is not protected from thermal precipitation by sodium caprylate and is not precipitated by rabbit anti-albumin anti-serum. It can be hydrolyzed by trypsin to yield monoiodotyrosine and another amino-acid that may be thyroxine. Two other iodinated substances released after hydrolysis were not identified.