Isolation and characterization of enzyme activities deiodinating thyroid hormone

textabstractIt is well established that in man peripheral deiodination of T4 accounts for most of the biologically active T3 and virtually all of the inactive rT3• In several situations reciprocal changes in serum T3 and rT3 levels occur, which indicates that enzymatic deiodination is not an uncontrolled process. To get more insight into the regulation and mechanism of thyroid hormone metabolism, basic knowledge of the deiodinating enzyme(s) is necessary. Therefore, the aim of this study was to localize, purify and characterize the iodothyronine deiodinase( s). The availability of pure enzyme preparations will not only facilitate the elucidation of the molecular mechanism of thyroid hormone regulation, but also answer the question of whether one or two enzymes are involved in the deiodination of T4• In Chapter 2, in vitro observations of the enzymatic deiodination of iodothyronines are described. In addition to a review of the literature, results from my own work are also included. The results of this work are discussed in relation to the findings by other investigators.In the following chapters, which are papers already published, my investigations of the enzymatic deiodination of several iodothyronines in rat liver preparations are described in detail