Monodeiodination of thyroxine to 3,3',5'-triiodothyronine in the human placenta.

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  • SUZUKI MICHIKO
    Second Department of Internal Medicine, Tohoku University School of Medicine
  • YOSHIDA KATSUMI
    Second Department of Internal Medicine, Tohoku University School of Medicine
  • SAKURADA TOSHIRO
    Second Department of Internal Medicine, Tohoku University School of Medicine
  • KITAOKA HIROFUMI
    Second Department of Internal Medicine, Tohoku University School of Medicine
  • KAISE KAZURO
    Second Department of Internal Medicine, Tohoku University School of Medicine
  • KAISE NOBUKO
    Second Department of Internal Medicine, Tohoku University School of Medicine
  • FUKAZAWA HIROSHI
    Second Department of Internal Medicine, Tohoku University School of Medicine
  • YAMAMOTO MAKIKO
    Second Department of Internal Medicine, Tohoku University School of Medicine
  • SAITO SHINTARO
    Second Department of Internal Medicine, Tohoku University School of Medicine
  • YOSHINAGA KAORU
    Second Department of Internal Medicine, Tohoku University School of Medicine

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Other Title
  • Monodeiodination of Thyroxine to 3,3′,5′-Triiodothyronine in the Human Placenta
  • Monodeiodination of Thyroxine to 3 3 5

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Abstract

SUZUKI, M., YOSHIDA, K., SAKURADA, T., KITAOKA, H., KAISE, K., KAISE, N., FUKAZAWA, H., YAMAMOTO, M., SAITO, S. and YOSHINAGA, K. Monodeiodination of Thyroxine to 3, 3', 5'-Triiodothyronine in the Human Placenta. Tohoku J. exp. Med., 1983, 140 (3), 311-318-We studied the characteristics of monodeiodination of thyroxine to T3 and reverse T3 in the human placenta which was obtained at normal delivery. The placentas were homogenized in cold sucrose Tris-HCl buffer, pH 7.5. The microsomal fraction was incubated at 37°C in the air for 1hr with 2μg of T4 in the presence of 0.05M DTT. The T3 and reverse T3 generated in the reaction mixture were extracted into cold ethanol and measured by RIA. Among the usual subcellular fractions of the placental homogenate, microsomas were most potent in deiodinating T4 to reverse T3, 17.9ng/mg protein/μg T4/60min. In microsome, production of reverse T3 from T4 was dependent upon protein concentration, incubation temperature, incubation time, pH and T4 concentration, and unstable to prior heating of the microsomal fraction. The production of T3 from T4 was negligible in the present system. Degradation of T3 in the human placenta was rapid. Although addition of anti-T3 antibody to the reaction mixture suppressed the degradation of T3, it had no effect on the net production of T3, suggesting that the obtained net T3 production rate had not been influenced by its degradation. Degradation of reverse T3 was negligible. These results indicate that the human placenta actively deiodinates T4 to reverse T3 enzymatically. This enzyme system might have some influence on the transplacental passage of thyroid hormone from the mother to the fetus.

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