title: Subcellular distribution of thyroxine 5'-deiodinase in the rat kidney: a plasma membrane location.
abstract: The enzymatic activity in rat kidney homogenates mediating the conversion of T4 to T2 has been previously shown to be particulate. The subcellular organelle responsible for T4 5'-deiodination, however, has not been identified. Enzymatic activity was assessed with outer ring 125I-labeled L-T4 as the substrate and the iodothyronines were separated by descending paper chromatography. Comparison of the distribution of T4 5'-deiodinase activity with that of established enzyme markers of subcellular organelles demonstrated: 1) T4 5'-deiodinase activity paralleled that of plasma membrane enzyme markers in subcellular fractions prepared by differential centrifugation, with 80% of the T4 5'-deiodinase and (Na+/K+)-ATPase equally distributed in the crude nuclear and microsomal fractions; 2) the smooth microsomal fraction, known to be contaminated with plasma membrane in kidney tissue preparations, contained the bulk of the T4 5'-deiodinase activity and plasma membrane marker enzymes found in the microsomal fraction; and 3) purified plasma membrane showed enrichment of T4 5'-deiodinase comparable to that of the known plasma membrane enzyme (Na+/K+)-ATPase. These data suggest that T4 5'-deiodinase in kidney tissue is an enzyme of the plasmalemma.
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000201:enzymology; D004229:Dithiothreitol / Q000494:pharmacology; D007453:Iodide Peroxidase / Q000032:analysis / Q000378:metabolism*; D007668:Kidney / Q000201:enzymology*; D008297:Male; D010544:Peroxidases / Q000378:metabolism*; D051381:Rats; D013347:Subcellular Fractions / Q000201:enzymology; D013974:Thyroxine
chemical_list: D010544:Peroxidases; D007453:Iodide Peroxidase; D013974:Thyroxine; D004229:Dithiothreitol