کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
1222567 1494670 2012 9 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
The site-specific basicity of thyroid hormones and their precursors as regulators of their biological functions
موضوعات مرتبط
مهندسی و علوم پایه شیمی شیمی آنالیزی یا شیمی تجزیه
پیش نمایش صفحه اول مقاله
The site-specific basicity of thyroid hormones and their precursors as regulators of their biological functions
چکیده انگلیسی

The complete macro- and microequilibrium analyses of thyroxine, liothyronine, reverse liothyronine and their biological precursors – diiodotyrosine, monoiodotyrosine and tyrosine are presented. Their biosyntheses, receptor- and transport protein-binding are shown to be distinctively dependent on the phenolate basicity. The protonation macroconstants were determined by 1H NMR-pH and/or UV-pH titrations. Microconstants of the minor microspecies were determined by deductive methods, in which O-methylated and carboxymethylated derivatives were synthesized, and the combination of their NMR-pH and UV-pH titration provided the experimental base to evaluate all the microconstants. NMR-pH profiles, macro-, and microscopic protonation schemes, and species-specific diagrams are included.Biosyntheses of the thyroid hormones take place by oxidative coupling of two iodotyrosine residues catalyzed by thyreoperoxidase in thyreoglobulin. On the grounds of our phenolate microconstants of precursors the thyroxine over liothyronine ratio needs to be 9:1 after their biosynthesis in thyroid gland, which is in good agreement with biochemical data. The microconstants show that the phenolates are in proton donor (–OH) form in liothyronine whereas they occur in proton acceptor (–O−) form in thyroxine at the pH of blood. These facts explain several facts that have previously been empirically known: the affinity of liothyronine for the receptor is higher than that of thyroxine, the affinity of thyroxine for the transport proteins is higher than that of liothyronine and the selectivity of thyroxine for the OATP1C1 organic anion transporter is higher than that of liothyronine.


► The protonation macro- and microconstants of thyroid hormones were determined.
► The results were interpreted in terms of biological functions.
► Protonation states of thyroid hormones are crucial for their biochemical functions.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Journal of Pharmaceutical and Biomedical Analysis - Volume 61, 5 March 2012, Pages 156–164
نویسندگان
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