“The Importance of a Phenolic Group in the Substrates of Iodotyrosine Deiodinase”

Iodotyrosine deiodinase (IYD) is an enzyme that is responsible for recycling iodide from monoiodotyrosine (I‐Tyr) and diiodotyrosine (I 2 ‐Tyr), which are formed as side‐products during the biosynthesis of thyroid hormones. Recently, a gene encoding IYD was found in bacterium Haliscomenobacter hydrossis (hhIYD), but the function of hhIYD in this organism is still unknown. This bacterium does not generate thyroid hormone and is not known to require iodide salvage. HhIYD can bind and deiodinate 2‐iodophenol, but not as efficiently as I‐Tyr. We wanted to know how broad the substrate specificity for this enzyme is; thus, the goal of the project is to learn how important the OH‐group of I‐Tyr is for catalysis. Since aryl amine and hydroxyl groups have common properties, we synthesized the aniline derivative of I‐Tyr. Both OH‐ and NH 2 ‐groups are electron donating substituents to the phenyl ring and can participate in hydrogen bonding. Moreover, we can propose a similar mechanism for deiodination of both I‐Tyr and its aniline derivative. We expressed and purified hhIYD. The binding of the aniline derivative to hhIYD was measured using fluorescence quenching, but no binding was observed even at a ligand concentration as high as 1370 μM. We also tested deiodination of the aniline derivative of I‐Tyr by hhIYD, but no deiodination was detected above turnover number of 7.05 × 10 −5 s −1 . We expect that this project will help to identify the full catalytic potential of IYD and its role in nature. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .