Cytosol components from human placenta and rat liver in iodothyronine 5- and 5'-deiodination.
Using either human placental microsomal 5-deiodinase as enzyme (5-DI) and thyroxine as substrate or rat liver (RL) microsomal 5'-deiodinase (5'DI) as enzyme and reverse [(3'- or 5'-)-125I]triiodo-L-thyronine ([125I]rT3) as substrate, activation of 5'-DI in the presence of NADPH was observed using either human placental or rat liver cytosolic components, but there was no activation of 5-DI. Both could be activated by DTT, with higher concentrations being required for 5-DI than for 5'-DI. Iopanoic acid, dicumarol, and sodium arsenite inhibited 5'-DI and 5-DI activated by DTT. In the presence of DTT, 1 mM 6-propyl-2-thiouracil had no effect on 5-DI but inhibited 5'DI. Thus, human placental and rat liver cytosolic components are interchangeable in activating hepatic 5'-DI in the presence of NADPH. However, if an endogenous cofactor system involved in the activation of human placental 5-DI exists, it probably differs from the activator of liver 5'-DI.
Iwase
K
K
Thyroid Research Laboratory, Mount Sinai Hospital Research Institute, Toronto, Ont., Canada.
Hummel
B C
BC
Walfish
P G
PG
D000818:Animals; D003600:Cytosol / Q000378:metabolism*; D004926:Escherichia coli; D005260:Female; D006801:Humans; D007453:Iodide Peroxidase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008862:Microsomes, Liver / Q000032:analysis*; D010920:Placenta / Q000032:analysis*; D011247:Pregnancy; D051381:Rats; D013879:Thioredoxins / Q000494:pharmacology
D013879:Thioredoxins; D007453:Iodide Peroxidase