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The Thyroxine Content of Thyroactive Iodinated Proteins as Determined by a Radioactive Isotope Dilution Technique¹

Department of Physiology and Pharmacology, Michigan State College, East Lansing

ABSTRACT

A procedure is described for the determination of thyroxine in thyroactive iodinated proteins by an isotope dilution technique employing radioactive thyroxine. It is shown that during hydrolysis in 40% barium hydroxide solution and subsequent isolation no significant exchange of iodine occurs between radioactive thyroxine and iodide. Analyses on seven different samples yielded an average true thyroxine value of 1.04 ± 0.049%. The average apparent thyroxine content (n-butanol soluble fraction) was 3.24 ± 0.429%. The "true" thyroxine thus comprised roughly one-third of the apparent thyroxine value.

¹ Published with the approval of the Directer of the Michigan Agricultural Experiment Station as Journal Series No. 1566. N. S.