Synthesis of Thyroxine by L-Amino Acid Oxidase

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Abstract
Thyroxine (T4) was identified as a product of the reaction between 4-hydroxy- 3,5-diiodophenylpyruvic acid (DIHPPA) and 3,5-diiodotyrosine (DIT), in confirmation of previous findings (1, 2). The synthesis of T4 from DIHPPA and DIT suggested that T4 may be formed during the incubation of DIT with l-amino acid oxidase. The effect of Lamino acid oxidase on DIT was investigated previously (3, 4) but T4 was not identified as a product of the reaction. In the present study, T4 was identified as a product of the action of l-amino acid oxidase on DIT, and the synthesis of T4 by this reaction, as well as by the nonenzymatic reaction between DIT and DIHPPA, was inhibited by Tapazole, thiouracil, ascorbic acid, glutathione, ergothioneine, semicarbazide and bisulfite.