EC Explorer

1.21.99.4

thyroxine 5′-deiodinase

3,3′,5-triiodo-L-thyronine + iodide + acceptor + H⁺ = L-thyroxine + reduced acceptor

diiodothyronine 5′-deiodinase [ambiguous], iodothyronine 5′-deiodinase, iodothyronine outer ring monodeiodinase, type I iodothyronine deiodinase, type II iodothyronine deiodinase, thyroxine 5-deiodinase [misleading], L-thyroxine iodohydrolase (reducing)

3,3′,5-triiodo-L-thyronine,iodide:acceptor oxidoreductase (iodinating)

70712-46-8

The enzyme activity has only been demonstrated in the direction of 5′-deiodination, which renders the thyroid hormone more active. The enzyme consists of type I and type II enzymes, both containing selenocysteine, but with different kinetics. For the type I enzyme the first reaction is a reductive deiodination converting the -Se-H group of the enzyme into an -Se-I group; the reductant then reconverts this into -Se-H, releasing iodide.

created 1984 as EC 3.8.1.4, transferred 2003 to EC 1.97.1.10, transferred 2015 to EC 1.21.99.4