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 abolishe...

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Bibliographic Details
Published in:Biochemical journal 1975-09, Vol.150 (3), p.489-493
Main Authors: Visser, Theo J, Van Der Does-Tobé, Ineke, Docter, Roel, Hennemann, Georg
Format: Article
Language:English
Subjects:
Animals
In Vitro Techniques
Liver - enzymology
Liver - metabolism
Male
Monoiodotyrosine - pharmacology
NAD - pharmacology
Propylthiouracil - pharmacology
Radioimmunoassay
Rats
Temperature
Thyroxine - metabolism
Triiodothyronine - biosynthesis
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Summary: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.
ISSN:0264-6021
1470-8728
DOI:10.1042/bj1500489