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Jacques Nunez - One of the best experts on this subject based on the ideXlab platform.
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kinetics of thyroglobulin Iodination and thyroid hormone synthesis catalyzed by peroxidases the role of h2o2
FEBS Journal, 2005Co-Authors: Alain Virion, Danièle Deme, J. Pommier, Jacques NunezAbstract:1 When thyroglobulin Iodination by thyroid peroxidase or lactoperoxidase is studied with optimal concentrations of H2O2-generating system, thyroid hormone synthesis (coupling reaction) begins after a constant lag period which is independent of the concentration of iodide, thyroglobulin or enzyme. Increasing the concentration of the H2O2-generating system inhibited the Iodination reaction whereas the length of the lag period was decreased. When thyroglobulin containing iodinated tyrosine residues but no hormone was incubated with increasing concentrations of iodide and limiting amounts of the H2O2-generating system the Iodination reaction was stimulated and the coupling reaction was inhibited. 2 To analyze whether the Iodination and coupling reactions require different enzyme-H2O2 species the Iodination and coupling reactions and the absorbance at 430 nm (compound II) were measured simultaneously with lactoperoxidase. Under these conditions: (a) the coupling reaction occurred only in the presence of sufficient amounts of H2O2 whereas the level of Iodination was the same; (b) an increase in absorbance at 430 nm was observed only when the Iodination reaction leveled off, i.e. just before the beginning of the coupling reaction; (c) during the lag period, i.e. the Iodination step, the only enzyme species seen in the Soret region was the native enzyme; and (d) adding iodinated thyroglobulin containing no hormone to preformed compound II or III resulted in a prompt coupling reaction. These data suggest that the Iodination and coupling reactions are catalyzed by different enzyme-H2O2 species. 3 When thyroid peroxidase or lactoperoxidase were preincubated for varying periods of time in the presence of the H2O2-generating system their activity towards guaiacol decreased progressively: with thyroid peroxidase the Km for guaiacol was increased 10-fold after 5 min of preincubation and 40-fold with lactoperoxidase. The activity of the preincubated enzymes was restored by iodide. Preincubated lactoperoxidase had the Soret spectrum of compound III. Similarly, the rate of Iodination of thyroglobulin was inhibited with the preincubated enzyme, but increasing the iodide concentration restored the iodinating activity. 4 The proposal is made that different enzyme-H2O2 species are the active agents in the catalysis of the Iodination and coupling reaction respectively.
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the role of lactoperoxidase h2o2 compounds in the catalysis of thyroglobulin Iodination and thyroid hormone synthesis
FEBS Journal, 2005Co-Authors: Francoise Courtin, Alain Virion, Jean-luc Michot, Danièle Deme, J. Pommier, Jacques NunezAbstract:Lactoperoxidase catalyzes successively, as thyroid peroxidase, the Iodination of several tyrosyl residues of thyroglobulin and the coupling of some of them to thyroid hormones. We show the following results in this paper. 1 The Iodination reaction is catalyzed by lactoperoxidase compound I whereas lactoperoxidase ‘compound II’ catalyzes the coupling reaction. Lactoperoxidase compound III catalyzes neither reaction. 2 Titration of lactoperoxidase ‘compound II’ by ferrocyanide showed that this enzyme-H2O2 species is two oxidizing equivalents above the native enzyme, and therefore constitutes a second form of lactoperoxidase ‘compound I’. These two forms of lactoperoxidase ‘compound I’ differ probably from one another in the localization of one of the two oxidizing equivalents either on porphyrin ring: π-compound I (compound I), or on the apoprotein: R°-compound 1 (‘compound II’). The difference in specificity between π-compound I and R°-compound I in catalyzing the Iodination and the coupling reaction respectively, might therefore depend differences both in the distribution of the two oxidizing equivalents and in the structure of the substrates. 3 In the presence of free diiodotyrosine, a halophenol which stimulates at very low concentrations the coupling reaction but has no effect on the Iodination reaction, the transfer of electrons between the substrate and lactoperoxidase R°-compound I is nearly stoichiometric: 1 mole of hormone is produced for each mole of lacto-peroxidase R°-compound I. Thus free diiodotyrosine seems to play the role of a very specific co-factor of the coupling reaction. 4 Iodide and SCN− also stimulate the coupling reaction when the H2O2/enzyme ratio used to prepare lactoperoxidase R°-compound I is higher than one. They do so by preventing the accumulation of the inactive derivative of lactoperoxidase, compound III, which is formed in the presence of excess H2O2. Iodide prevents the formation of compound III whereas SCN− very rapidly decomposes compound III back to the native enzyme.
Alain Virion - One of the best experts on this subject based on the ideXlab platform.
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kinetics of thyroglobulin Iodination and thyroid hormone synthesis catalyzed by peroxidases the role of h2o2
FEBS Journal, 2005Co-Authors: Alain Virion, Danièle Deme, J. Pommier, Jacques NunezAbstract:1 When thyroglobulin Iodination by thyroid peroxidase or lactoperoxidase is studied with optimal concentrations of H2O2-generating system, thyroid hormone synthesis (coupling reaction) begins after a constant lag period which is independent of the concentration of iodide, thyroglobulin or enzyme. Increasing the concentration of the H2O2-generating system inhibited the Iodination reaction whereas the length of the lag period was decreased. When thyroglobulin containing iodinated tyrosine residues but no hormone was incubated with increasing concentrations of iodide and limiting amounts of the H2O2-generating system the Iodination reaction was stimulated and the coupling reaction was inhibited. 2 To analyze whether the Iodination and coupling reactions require different enzyme-H2O2 species the Iodination and coupling reactions and the absorbance at 430 nm (compound II) were measured simultaneously with lactoperoxidase. Under these conditions: (a) the coupling reaction occurred only in the presence of sufficient amounts of H2O2 whereas the level of Iodination was the same; (b) an increase in absorbance at 430 nm was observed only when the Iodination reaction leveled off, i.e. just before the beginning of the coupling reaction; (c) during the lag period, i.e. the Iodination step, the only enzyme species seen in the Soret region was the native enzyme; and (d) adding iodinated thyroglobulin containing no hormone to preformed compound II or III resulted in a prompt coupling reaction. These data suggest that the Iodination and coupling reactions are catalyzed by different enzyme-H2O2 species. 3 When thyroid peroxidase or lactoperoxidase were preincubated for varying periods of time in the presence of the H2O2-generating system their activity towards guaiacol decreased progressively: with thyroid peroxidase the Km for guaiacol was increased 10-fold after 5 min of preincubation and 40-fold with lactoperoxidase. The activity of the preincubated enzymes was restored by iodide. Preincubated lactoperoxidase had the Soret spectrum of compound III. Similarly, the rate of Iodination of thyroglobulin was inhibited with the preincubated enzyme, but increasing the iodide concentration restored the iodinating activity. 4 The proposal is made that different enzyme-H2O2 species are the active agents in the catalysis of the Iodination and coupling reaction respectively.
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the role of lactoperoxidase h2o2 compounds in the catalysis of thyroglobulin Iodination and thyroid hormone synthesis
FEBS Journal, 2005Co-Authors: Francoise Courtin, Alain Virion, Jean-luc Michot, Danièle Deme, J. Pommier, Jacques NunezAbstract:Lactoperoxidase catalyzes successively, as thyroid peroxidase, the Iodination of several tyrosyl residues of thyroglobulin and the coupling of some of them to thyroid hormones. We show the following results in this paper. 1 The Iodination reaction is catalyzed by lactoperoxidase compound I whereas lactoperoxidase ‘compound II’ catalyzes the coupling reaction. Lactoperoxidase compound III catalyzes neither reaction. 2 Titration of lactoperoxidase ‘compound II’ by ferrocyanide showed that this enzyme-H2O2 species is two oxidizing equivalents above the native enzyme, and therefore constitutes a second form of lactoperoxidase ‘compound I’. These two forms of lactoperoxidase ‘compound I’ differ probably from one another in the localization of one of the two oxidizing equivalents either on porphyrin ring: π-compound I (compound I), or on the apoprotein: R°-compound 1 (‘compound II’). The difference in specificity between π-compound I and R°-compound I in catalyzing the Iodination and the coupling reaction respectively, might therefore depend differences both in the distribution of the two oxidizing equivalents and in the structure of the substrates. 3 In the presence of free diiodotyrosine, a halophenol which stimulates at very low concentrations the coupling reaction but has no effect on the Iodination reaction, the transfer of electrons between the substrate and lactoperoxidase R°-compound I is nearly stoichiometric: 1 mole of hormone is produced for each mole of lacto-peroxidase R°-compound I. Thus free diiodotyrosine seems to play the role of a very specific co-factor of the coupling reaction. 4 Iodide and SCN− also stimulate the coupling reaction when the H2O2/enzyme ratio used to prepare lactoperoxidase R°-compound I is higher than one. They do so by preventing the accumulation of the inactive derivative of lactoperoxidase, compound III, which is formed in the presence of excess H2O2. Iodide prevents the formation of compound III whereas SCN− very rapidly decomposes compound III back to the native enzyme.
Peng Yu - One of the best experts on this subject based on the ideXlab platform.
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concise synthesis of prenylated and geranylated chalcone natural products by regiospecific Iodination and suzuki coupling reactions
ChemInform, 2014Co-Authors: Haomeng Wang, Kui Lu, Kai Sheng, Peng YuAbstract:Based on the regioselective Iodination of the bis Mom-protected methyl aryl ketones (I) a convenient synthesis of bavachalcone (VIIa) and isoxanthoangelol (VIIb) is developed.
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regioselective Iodination of flavonoids by n iodosuccinimide under neutral conditions
ChemInform, 2014Co-Authors: Kui Lu, Haomeng Wang, Xiaoli Fu, Dewu Quan, Hongxia Ding, Peng YuAbstract:The Iodination can be conveniently directed to either the C-6 or C-8 position by changing the protection pattern at the C-5 OH group.
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concise synthesis of prenylated and geranylated chalcone natural products by regiospecific Iodination and suzuki coupling reactions
Tetrahedron Letters, 2014Co-Authors: Haomeng Wang, Kui Lu, Kai Sheng, Peng YuAbstract:Four natural chalcones bearing prenyl or geranyl groups, i.e., isobavachalcone (1), bavachalcone (2), xanthoangelol (3), and 2′,4′,4-trihydroxy-5′-geranylchalcone (isoxanthoangelol, 4) were synthesized by using a regio-selective Iodination and the Suzuki coupling reaction as key steps. Among them, the first total synthesis of 2′,4′,4-trihydroxy-5′-geranylchalcone was achieved in 36% overall yield. Comparing with the reported methods based on C-alkylation or O-alkylation followed by Claisen rearrangement to introduce the side chain, this new strategy capitalizes on a precious regiochemical control during Iodination. The overall yields for the synthesis of the first three chalcones were improved from 17% to 53%, 12% to 35%, and 28% to 50%, respectively.
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regioselective Iodination of flavonoids by n iodosuccinimide under neutral conditions
Tetrahedron Letters, 2013Co-Authors: Kui Lu, Haomeng Wang, Xiaoli Fu, Dewu Quan, Hongxia Ding, Peng YuAbstract:Abstract Regioselective synthesis of C-6 and C-8 monoiodo flavonoids, which are important intermediates for the synthesis of flavonoid natural products and drug molecules, was achieved by Iodination of suitably alkylated flavonoids with N -iodosuccinimide (NIS) in DMF. The Iodination gives either a C-6 or C-8 iodo flavonoid in high yield, depending on the protection pattern of the C-5 and C-7 OH groups. The mild and neutral conditions render this novel protocol particularly useful for the regioselective Iodination of acid-sensitive substrates.
Danièle Deme - One of the best experts on this subject based on the ideXlab platform.
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kinetics of thyroglobulin Iodination and thyroid hormone synthesis catalyzed by peroxidases the role of h2o2
FEBS Journal, 2005Co-Authors: Alain Virion, Danièle Deme, J. Pommier, Jacques NunezAbstract:1 When thyroglobulin Iodination by thyroid peroxidase or lactoperoxidase is studied with optimal concentrations of H2O2-generating system, thyroid hormone synthesis (coupling reaction) begins after a constant lag period which is independent of the concentration of iodide, thyroglobulin or enzyme. Increasing the concentration of the H2O2-generating system inhibited the Iodination reaction whereas the length of the lag period was decreased. When thyroglobulin containing iodinated tyrosine residues but no hormone was incubated with increasing concentrations of iodide and limiting amounts of the H2O2-generating system the Iodination reaction was stimulated and the coupling reaction was inhibited. 2 To analyze whether the Iodination and coupling reactions require different enzyme-H2O2 species the Iodination and coupling reactions and the absorbance at 430 nm (compound II) were measured simultaneously with lactoperoxidase. Under these conditions: (a) the coupling reaction occurred only in the presence of sufficient amounts of H2O2 whereas the level of Iodination was the same; (b) an increase in absorbance at 430 nm was observed only when the Iodination reaction leveled off, i.e. just before the beginning of the coupling reaction; (c) during the lag period, i.e. the Iodination step, the only enzyme species seen in the Soret region was the native enzyme; and (d) adding iodinated thyroglobulin containing no hormone to preformed compound II or III resulted in a prompt coupling reaction. These data suggest that the Iodination and coupling reactions are catalyzed by different enzyme-H2O2 species. 3 When thyroid peroxidase or lactoperoxidase were preincubated for varying periods of time in the presence of the H2O2-generating system their activity towards guaiacol decreased progressively: with thyroid peroxidase the Km for guaiacol was increased 10-fold after 5 min of preincubation and 40-fold with lactoperoxidase. The activity of the preincubated enzymes was restored by iodide. Preincubated lactoperoxidase had the Soret spectrum of compound III. Similarly, the rate of Iodination of thyroglobulin was inhibited with the preincubated enzyme, but increasing the iodide concentration restored the iodinating activity. 4 The proposal is made that different enzyme-H2O2 species are the active agents in the catalysis of the Iodination and coupling reaction respectively.
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the role of lactoperoxidase h2o2 compounds in the catalysis of thyroglobulin Iodination and thyroid hormone synthesis
FEBS Journal, 2005Co-Authors: Francoise Courtin, Alain Virion, Jean-luc Michot, Danièle Deme, J. Pommier, Jacques NunezAbstract:Lactoperoxidase catalyzes successively, as thyroid peroxidase, the Iodination of several tyrosyl residues of thyroglobulin and the coupling of some of them to thyroid hormones. We show the following results in this paper. 1 The Iodination reaction is catalyzed by lactoperoxidase compound I whereas lactoperoxidase ‘compound II’ catalyzes the coupling reaction. Lactoperoxidase compound III catalyzes neither reaction. 2 Titration of lactoperoxidase ‘compound II’ by ferrocyanide showed that this enzyme-H2O2 species is two oxidizing equivalents above the native enzyme, and therefore constitutes a second form of lactoperoxidase ‘compound I’. These two forms of lactoperoxidase ‘compound I’ differ probably from one another in the localization of one of the two oxidizing equivalents either on porphyrin ring: π-compound I (compound I), or on the apoprotein: R°-compound 1 (‘compound II’). The difference in specificity between π-compound I and R°-compound I in catalyzing the Iodination and the coupling reaction respectively, might therefore depend differences both in the distribution of the two oxidizing equivalents and in the structure of the substrates. 3 In the presence of free diiodotyrosine, a halophenol which stimulates at very low concentrations the coupling reaction but has no effect on the Iodination reaction, the transfer of electrons between the substrate and lactoperoxidase R°-compound I is nearly stoichiometric: 1 mole of hormone is produced for each mole of lacto-peroxidase R°-compound I. Thus free diiodotyrosine seems to play the role of a very specific co-factor of the coupling reaction. 4 Iodide and SCN− also stimulate the coupling reaction when the H2O2/enzyme ratio used to prepare lactoperoxidase R°-compound I is higher than one. They do so by preventing the accumulation of the inactive derivative of lactoperoxidase, compound III, which is formed in the presence of excess H2O2. Iodide prevents the formation of compound III whereas SCN− very rapidly decomposes compound III back to the native enzyme.
J. Pommier - One of the best experts on this subject based on the ideXlab platform.
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kinetics of thyroglobulin Iodination and thyroid hormone synthesis catalyzed by peroxidases the role of h2o2
FEBS Journal, 2005Co-Authors: Alain Virion, Danièle Deme, J. Pommier, Jacques NunezAbstract:1 When thyroglobulin Iodination by thyroid peroxidase or lactoperoxidase is studied with optimal concentrations of H2O2-generating system, thyroid hormone synthesis (coupling reaction) begins after a constant lag period which is independent of the concentration of iodide, thyroglobulin or enzyme. Increasing the concentration of the H2O2-generating system inhibited the Iodination reaction whereas the length of the lag period was decreased. When thyroglobulin containing iodinated tyrosine residues but no hormone was incubated with increasing concentrations of iodide and limiting amounts of the H2O2-generating system the Iodination reaction was stimulated and the coupling reaction was inhibited. 2 To analyze whether the Iodination and coupling reactions require different enzyme-H2O2 species the Iodination and coupling reactions and the absorbance at 430 nm (compound II) were measured simultaneously with lactoperoxidase. Under these conditions: (a) the coupling reaction occurred only in the presence of sufficient amounts of H2O2 whereas the level of Iodination was the same; (b) an increase in absorbance at 430 nm was observed only when the Iodination reaction leveled off, i.e. just before the beginning of the coupling reaction; (c) during the lag period, i.e. the Iodination step, the only enzyme species seen in the Soret region was the native enzyme; and (d) adding iodinated thyroglobulin containing no hormone to preformed compound II or III resulted in a prompt coupling reaction. These data suggest that the Iodination and coupling reactions are catalyzed by different enzyme-H2O2 species. 3 When thyroid peroxidase or lactoperoxidase were preincubated for varying periods of time in the presence of the H2O2-generating system their activity towards guaiacol decreased progressively: with thyroid peroxidase the Km for guaiacol was increased 10-fold after 5 min of preincubation and 40-fold with lactoperoxidase. The activity of the preincubated enzymes was restored by iodide. Preincubated lactoperoxidase had the Soret spectrum of compound III. Similarly, the rate of Iodination of thyroglobulin was inhibited with the preincubated enzyme, but increasing the iodide concentration restored the iodinating activity. 4 The proposal is made that different enzyme-H2O2 species are the active agents in the catalysis of the Iodination and coupling reaction respectively.
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the role of lactoperoxidase h2o2 compounds in the catalysis of thyroglobulin Iodination and thyroid hormone synthesis
FEBS Journal, 2005Co-Authors: Francoise Courtin, Alain Virion, Jean-luc Michot, Danièle Deme, J. Pommier, Jacques NunezAbstract:Lactoperoxidase catalyzes successively, as thyroid peroxidase, the Iodination of several tyrosyl residues of thyroglobulin and the coupling of some of them to thyroid hormones. We show the following results in this paper. 1 The Iodination reaction is catalyzed by lactoperoxidase compound I whereas lactoperoxidase ‘compound II’ catalyzes the coupling reaction. Lactoperoxidase compound III catalyzes neither reaction. 2 Titration of lactoperoxidase ‘compound II’ by ferrocyanide showed that this enzyme-H2O2 species is two oxidizing equivalents above the native enzyme, and therefore constitutes a second form of lactoperoxidase ‘compound I’. These two forms of lactoperoxidase ‘compound I’ differ probably from one another in the localization of one of the two oxidizing equivalents either on porphyrin ring: π-compound I (compound I), or on the apoprotein: R°-compound 1 (‘compound II’). The difference in specificity between π-compound I and R°-compound I in catalyzing the Iodination and the coupling reaction respectively, might therefore depend differences both in the distribution of the two oxidizing equivalents and in the structure of the substrates. 3 In the presence of free diiodotyrosine, a halophenol which stimulates at very low concentrations the coupling reaction but has no effect on the Iodination reaction, the transfer of electrons between the substrate and lactoperoxidase R°-compound I is nearly stoichiometric: 1 mole of hormone is produced for each mole of lacto-peroxidase R°-compound I. Thus free diiodotyrosine seems to play the role of a very specific co-factor of the coupling reaction. 4 Iodide and SCN− also stimulate the coupling reaction when the H2O2/enzyme ratio used to prepare lactoperoxidase R°-compound I is higher than one. They do so by preventing the accumulation of the inactive derivative of lactoperoxidase, compound III, which is formed in the presence of excess H2O2. Iodide prevents the formation of compound III whereas SCN− very rapidly decomposes compound III back to the native enzyme.