title: Re-examination of the subcellular localization of thyroxine 5'-deiodination in rat liver.
abstract: We describe the existence of at least two thyroxine 5'-deiodinases in rat liver. They co-fractionate with NADPH-cytochrome c reductase, the marker enzyme for membranes of the endoplasmic reticulum. Subcellular-localization studies of the most active microsomal thyroxine 5'-deiodinase were performed under substrate saturation and at optimal pH 6.8. This enzyme was a Km(app.) of about 3 microM-thyroxine and a Vmax. of about 8 ng of tri-iodothyronine/min per mg of protein. Our study confirms in part the earlier reports of microsomal localization of thyroxine 5'-deiodination. However, this process is not mediated by only a single enzyme.
mesh_terms: D000818:Animals; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000201:enzymology / Q000378:metabolism*; D008297:Male; D011506:Proteins / Q000378:metabolism; D051381:Rats; D013347:Subcellular Fractions / Q000201:enzymology / Q000378:metabolism; D013974:Thyroxine / Q000378:metabolism*
chemical_list: D011506:Proteins; D013974:Thyroxine