Thyroid Hormone Regulates Rat Placental Type III Iodothyronine Deiodinase Activity by Inducing Kinetic Changes Different from Those in the Same Isozyme in Rat Brain

Endocrine Journal

YOSHIHIKO AIZAWA²  KYOU KIKUCHI²  NORIYO SAYAMA²  YOSHINORI KISO²  HIROSHI FUKAZAWA²  KOUKI MORI²  KEISHI ABE²  KATSUMI YOSHIDA¹ 

[1] Department of Clinical Biology and Hormonal Regulation, Tohoku University School of Medicine;Second Department of Internal Medicine, Tohoku University School of Medicine

关键词: 5-Deiodinase;    Thyroid hormone;    Phospholipids;    Placenta;    Brain;   

DOI  :  10.1507/endocrj.42.753

学科分类：内分泌与代谢学

来源: Japan Endocrine Society

【 摘 要 】

References(30)Cited-By(4)The kinetics of type III iodothyronine deiodinase (5-D) in rat placenta and brain and the role of phospholipids in enzyme activity were determined. Pregnant Sprague-Dawley rats were given either vehicle (control group) or T4 (15μg/100g bw/day; hyperthyroid group) from the 14th to the 21st day of gestation. Mitochondrial-microsomal fractions of the placenta and brain were used as the source of T4 5-D. Placental T4 5-D activity in the hyperthyroid group was increased when determined at 13nM T4, but it was not significantly different from the control value when assayed at 1.3μM T4. In contrast, T4 5-D in the brain was significantly increased in the hyperthyroid group regardless of the substrate concentration. Hyperthyroid rats showed decreased Km for placental 5-D and increased Vmax for brain 5-D. CM-Sephadex chromatography of solubilized placental microsomes was performed to determine whether phospholipids cause a reduction in the Km of placental 5-D in hyperthyroid rats. T3 5-D activity was undetectable unless protein-containing fractions were combined with phospholipid-containing fractions in the reaction mixture. Kinetic studies revealed that phospholipids had no effects on either Km or Vmax of placental T3 5-D. These data indicate that 5-D activity in the rat placenta is increased in hyperthyroidism with different kinetic changes from those in the brain, and that phospholipids have no effects on the kinetic parameters of placental 5-D whereas they are essential for the enzyme activity.

【 授权许可】

Unknown