Conversion of thyroxine into tri-iodothyronine by rat liver homogenate.
By using a highly specific radioimmunoassay the formation of tri-iodothyronine by the deiodination of thyroxine was studied in rat liver homogenate. Several observations suggest that the reaction observed is enzymic in nature. Pre-heating the homogenate for 30 min at 56 degrees C completely abolished conversion of thyroxine into tri-iodothyronine; the component of rat liver homogenate responsible could be saturated with substrate; iodotyrosines displayed competitive activity. Between 0 degrees and 37 degrees C, the tri-iodothyronine-production rate was positively correlated with incubation temperature. The addition of NAD+ enhanced conversion into tri-iodothyronine, which suggests that an oxidative mechanism is involved. 5-Propyl-2-thiouracil and 6-propyl-2-thiouracil, both known to prevent deiodination in vivo, greatly decreased the deiodiantion activity of rat liver homogenate.
D000818:Animals; D066298:In Vitro Techniques; D008099:Liver / Q000201:enzymology / Q000378:metabolism*; D008297:Male; D007470:Monoiodotyrosine / Q000494:pharmacology; D009243:NAD / Q000494:pharmacology; D011441:Propylthiouracil / Q000494:pharmacology; D011863:Radioimmunoassay; D051381:Rats; D013696:Temperature; D013974:Thyroxine / Q000378:metabolism*; D014284:Triiodothyronine / Q000096:biosynthesis*
D014284:Triiodothyronine; D009243:NAD; D011441:Propylthiouracil; D007470:Monoiodotyrosine; D013974:Thyroxine