ID 1.21.99.4 DE thyroxine 5'-deiodinase. AN diiodothyronine 5'-deiodinase. AN iodothyronine 5'-deiodinase. AN iodothyronine outer ring monodeiodinase. AN L-thyroxine iodohydrolase (reducing). AN thyroxine 5-deiodinase. AN type II iodothyronine deiodinase. AN type I iodothyronine deiodinase. CA 3,3',5-triiodo-L-thyronine + A + H(+) + iodide = AH2 + L-thyroxine. CC -!- The enzyme activity has only been demonstrated in the direction of CC 5'-deiodination, which renders the thyroid hormone more active. CC -!- The enzyme consists of type I and type II enzymes, both containing CC selenocysteine, but with different kinetics. CC -!- For the type I enzyme the first reaction is a reductive deiodination CC converting the -Se-H group of the enzyme into an -Se-I group; the CC reductant then reconverts this into -Se-H, releasing iodide. CC -!- Formerly EC 1.97.1.10 and EC 3.8.1.4. DR P49894, IOD1_CANLF ; O42411, IOD1_CHICK ; Q6V915, IOD1_FELCA ; DR Q804E1, IOD1_FUNHE ; P49895, IOD1_HUMAN ; Q61153, IOD1_MOUSE ; DR O42449, IOD1_ORENI ; Q6QN13, IOD1_PIG ; A4GT88, IOD1_RABIT ; DR P24389, IOD1_RAT ; Q95N00, IOD1_SUNMU ; Q2QEI3, IOD1_XENLA ; DR P49896, IOD2_AQUCT ; Q5I3B2, IOD2_BOVIN ; Q9IAX2, IOD2_CHICK ; DR P79747, IOD2_FUNHE ; Q92813, IOD2_HUMAN ; Q9Z1Y9, IOD2_MOUSE ; DR Q8UVX8, IOD2_NEOFS ; L7WGA7, IOD2_PETMA ; Q6QN12, IOD2_PIG ; DR P70551, IOD2_RAT ; Q6U6H1, IOD_HALRO ; //