Metabolism of monoiodotyrosine, diiodotyrosine, triiodothyronine and thyroxine by L-amino acid oxidase.

Abstract

Thyroxine, triiodothyronine, diiodotyrosine and monoiodotyrosine, labelled with I131, were incubated with L-amino acid oxidase of cobra venom, and their metabolites studied by paper chromatography and radioautography. Under these conditions, the iodinated tyrosines were converted to the corresponding alpha-keto acid and acetic acid, inorganic iodide, and a number of unknown compounds. The deiodination of iodotyrosines by L-amino acid oxidase occurred after their corresponding alpha keto acids were formed by deamination of theamino acids. Triiodothyronine and thhyroxine were converted to their respective acetic acid derivatives, but not to inorganic iodide. The rate of degradation of these aromatic iodinated compounds by L-amino acid oxidase was related to the number of iodine atoms in the phenyl or diphenyl ether radical; i.e. monoiodotyrosine→diiodotyrosine→triiodothyronine→thyroxine.