Studies on the degradation of thyroid hormones in vitro with compounds labelled in either ring

Abstract

[3:5-I1312]Thyroxine has been incubated with extracts of rat liver and it was found that deiodination from the thyroxine [alpha] ring occurs very slightly or not at all. Experiments with [3'':5''-I1312]thyrox-ine confirmed previous findings that the iodine atoms on the [beta] ring are released as inorganic iodide. Organic metabolites were produced which adhered to the protein of the liver extract. These contained the iodine from the [alpha] ring, since on treatment with alkali they yielded 3:5-di-iodo-tyrosine and 4-hydroxy-3:5-di-iodophenyl-lactic acid. The possible identity of these metabolites is discussed.