Document Detail

Thyroid hormone regulates rat placental type III iodothyronine deiodinase activity by inducing kinetic changes different from those in the same isozyme in rat brain.
MedLine Citation:
PMID:  8822316     Owner:  NLM     Status:  MEDLINE    
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 (15 micrograms/100 g 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 13 nM T4, but it was not significantly different from the control value when assayed at 1.3 microM 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.
K Mori; K Yoshida; H Fukazawa; Y Kiso; N Sayama; K Kikuchi; Y Aizawa; K Abe
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Publication Detail:
Type:  Comparative Study; Journal Article    
Journal Detail:
Title:  Endocrine journal     Volume:  42     ISSN:  0918-8959     ISO Abbreviation:  Endocr. J.     Publication Date:  1995 Dec 
Date Detail:
Created Date:  1996-11-14     Completed Date:  1996-11-14     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  9313485     Medline TA:  Endocr J     Country:  JAPAN    
Other Details:
Languages:  eng     Pagination:  753-60     Citation Subset:  IM    
Second Department of Internal Medicine, Tohoku University School of Medicine, Sendai, Japan.
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MeSH Terms
Brain / enzymology*
Cerebral Cortex / metabolism
Hyperthyroidism / enzymology
Iodide Peroxidase / metabolism*
Isoenzymes / metabolism*
Liver / enzymology
Organ Specificity
Phospholipids / physiology
Placenta / enzymology*
Rats, Sprague-Dawley
Thyroxine / blood*
Triiodothyronine / blood*
Reg. No./Substance:
0/Isoenzymes; 0/Phospholipids; 6893-02-3/Triiodothyronine; 7488-70-2/Thyroxine; EC Peroxidase

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