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J. L. LEONARD, I. N. ROSENBERG, Subcellular Distribution of Thyroxine 5′-Deiodinase in the Rat Kidney: A Plasma Membrane Location, Endocrinology, Volume 103, Issue 1, 1 July 1978, Pages 274–280, https://doi.org/10.1210/endo-103-1-274
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The enzymatic activity in rat kidney homogenates mediating the conversion of T4 to T3 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 ki ney 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.
