Bacterial and mammalian thioredoxin systems activate iodothyronine 5′-deiodination

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Abstract
The identity of a dithiol (designated DFB) of relative mass (Mr) = 13 000, reported previously to be present infraction B of rat liver cytosol and to participate as a cofactor in the 5′-deiodination of iodothyronines, has been investigated. Substitution of highly purified thioredoxin from Escherichia coli for fraction B or of highly purified thioredoxin reductase from either E. coli or rat liver for cytosolic fraction A (containing DFB reductase) permits deiodination of 3,3′,5′-[l25I]triiodothyronine by rat liver microsomes to proceed. Addition of antibodies to highly purified rat-liver thioredoxin or thioredoxin reductase inhibits deiodination. Thus, the thioredoxin system largely accounts for the activity of the cytosolic cofactor system supporting 5′-deiodination of 3,3′,5′-triiodothyronine in rat liver.