Iodotyrosine deiodinase (IYD) is unusual in its reliance on flavin to promote reductive dehalogenation of halotyrosines under aerobic conditions. Applications of this activity can be envisioned for bioremediation, but expansion of its specificity requires an understanding of the mechanistic steps that limit the rate of turnover. Key processes capable of controlling steady-state turnover have now been evaluated and described in this study. While proton transfer is necessary for converting the electron-rich substrate into an electrophilic intermediate suitable for reduction, kinetic solvent deuterium isotope effects suggest that this process does not contribute to the overall efficiency of catalysis under neutral conditions. Similarly, reconstituting IYD with flavin analogues demonstrates that a change in reduction potential by as much as 132 mV affects k cat by less than 3-fold. Furthermore, k cat/K m does not correlate with reduction potential and indicates that electron transfer is also not rate determining. Catalytic efficiency is most sensitive to the electronic nature of its substrates. Electron-donating substituents on the ortho position of iodotyrosine stimulate catalysis and conversely electron-withdrawing substituents suppress catalysis. Effects on k cat and k cat/K m range from 22- to 100-fold and fit a linear free-energy correlation with a ρ ranging from −2.1 to −2.8 for human and bacterial IYD. These values are consistent with a rate-determining process of stabilizing the electrophilic and nonaromatic intermediate poised for reduction. Future engineering can now focus on efforts to stabilize this electrophilic intermediate over a broad series of phenolic substrates that are targeted for removal from our environment.

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Four-component reactions of 3-amino-1,2,4-triazole or 5-amino-1H-pyrazole-4-carbonitrile with aromatic aldehydes and pyruvic acid or its esters under ultrasonication were studied. Unusual for such a reaction type, a cascade of elementary stages led to the formation of 7-azolylaminotetrahydroazolo[1,5-a]pyrimidines.

Iodotyrosine deiodinase (IYD) is an enzyme that is responsible for recycling iodide from monoiodotyrosine (I‐Tyr) and diiodotyrosine (I2‐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 NH2‐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.