US EPA

1372475 

Journal Article 

Cytosol components from human placenta and rat liver in iodothyronine 5- and 5'-deiodination 

Iwase, K; Hummel, BC; Walfish, PG 

1989 

Yes 

Biochemistry and Cell Biology
ISSN: 0829-8211
EISSN: 1208-6002 

NATL RESEARCH COUNCIL CANADA 

OTTAWA 

67 

1 

58-63 

English 

2653382 

WOS:A1989T384700009 

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.