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In Vitro Formation of Apparent Covalent Complexes Between L-Triiodothyronine and Plasma Protein¹

Endocrine Research Laboratory, Department of Medicine, Montefiore Hospital and Medical Center, and Albert Einstein College of Medicine Bronx, N. Y.

Nondissociable complexes between ¹²⁵I-labeled T₃ (¹²⁵I-T₃) and plasma proteins were observed after incubation of ¹²⁵I-T₃ with plasma diluted 200-fold with phosphate buffer. The formation of these complexes was enhanced in the presence of Cu²⁺ and flavin mononucleotide and inhibited by reducing agents such as propylthiouracil, thiosulfate, dithiothreitol, and glutathione. The ¹²⁵I-T₃ protein complexes could be disrupted after digestion with pronase. T₃ itself was identified as a constituent of the pronase digests by co-chromatography with authentic ¹³¹I-T₃ to a constant isotopic ratio across the T₃ area. Since treatment with 0.2% sodium dodecylsulfate or 8M urea did not disrupt the complexes, the T₃-protein bond appears to have some of the characteristics of a covalent bond between hormone and protein.

¹ Supported by USPHS Grant 9 R01-AM-15241-12, and U.S. Army Contract DA-49-193-MD-2967.

² Career Scientist of the Health Research Council of New York City, Award 1-222.

Received February 7, 1972.