A photoactivated flavin-induced degradation of thyroxine and related phenols.

Abstract

Previous experiments had revealed that deiodination of thyroid hormones occurred in preparations of frog tissues supplemented with flavin compounds, and that this effect was especially marked in preboiled specimens. The present study was therefore undertaken to investigate a possible direct chemical interaction between flavin derivatives and iodinated phenols. Marked degradation of thyroxine (D- and L-isomers), triiodothyronine, tetra- and triiodothyroacetic acids and mono- and diiodotyrosine occurred when these compounds were incubated in a simple buffer medium (KRP) in the presence of flavin compounds and bright light. This degradation proceeded less rapidly in ambient light and was completely prevented by incubation in either total darkness or in red light. The photoactivated flavin-induced degradation of thyroxine was inhibited by anoxia, and by human plasma (provided this was added to the system before the flavin). The rate of the reaction was reduced in the presence of catalase. Certain hydroxylated...