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At least 19 recordsLinked to original sources
PubMed1978

Cofactor role of iodide in peroxidase antimicrobial action against Escherichia coli.

The mechanism of antimicrobial activity of the peroxidase-hydrogen peroxide (H(2)O(2))-iodide (I(-)) system was investigated. Inhibition of respiration and loss of viability of Escherichia coli were used as measures of antimicrobial activity. Because the bacteria destroyed H(2)O(2), peroxidase antimicrobial action depended on the competition for H(2)O(2) between the bacteria and the peroxidase. Utilization of H(2)O(2) by the peroxidase was favored by (i) increasing either the peroxidase or the I(-) concentration, so as to increase the rate of oxidation of I(-), (ii) lowering the temperature to lower the rate of destruction of H(2)O(2) by the bacteria, and (iii) adding H(2)O(2) in small increments so as to avoid a large excess of H(2)O(2) relative to I(-). When utilization of H(2)O(2) by the peroxidase system was favored, the peroxidase system and iodine (I(2)) were equivalent. That is, antimicrobial action per mole of H(2)O(2) equaled that per mole of I(2). Also, identical antimicrobial action was obtained either by incubating the bacteria directly with the peroxidase system or by preincubating the peroxidase system so as to form I(2) and then adding the bacteria. On the other hand, peroxidase antimicrobial action could be obtained at low I(-) concentrations. These I(-) concentrations were lower than the concentration of I(2) that was required for antimicrobial action. It is proposed that peroxidase-catalyzed oxidation of I(-) yields I(2), which reacts with bacterial components to yield the oxidized components and I(-). The I(-) that is released can be reoxidized and participate again in the oxidation of bacterial components. In this way, I(-) acts as a cofactor in the peroxidase-catalyzed oxidation of bacterial components.

Coenzymes↗
PubMedDate not supplied

[Histochemical characteristics of some oxidation-reduction hydrolytic enzymes in different forms of goiter].

Histochemical study of some enzymatic systems was conducted in various form of goiter. A study was made of the thyroid gland tissue obtained during the operation in 96 patients. Euthyrosis was accompanied by a decrease in the succinic dehydrogenase, cytochromoxidase, iodide peroxidase, acid and alkaline phosphatase activity. As to thyrotoxic goiter - it displayed an increase in the activity of these enzymes and desquamation of the follicular epithelium; the rejected cells possessed a high acid phosphatase activity. In comparison with thyrotoxic goiter, Askinazi's cell count was increased in the euthyroid macrofollicular nodular and diffuse goiter.

Acid Phosphatase↗
PubMed1979

Peroxidase activity and iodide uptake in hormone-responsive and hormone-independent GR mouse mammary tumors.

Transplanted mammary tumors growing in the inbred GR/AFib mouse were assayed for peroxidase activity and ability to concentrate injected 125I. Both tumor peroxidase activity and iodide uptake were about ten times greater in the hormone-resonsive (HR) tumors than in the hormone-independent tumors. However, although peroxidases are known for their ability to participate in the iodination of proteins, over 90% of the radioactive iodine found in the tumors was shown to be free iodide. This finding suggests that these two parameters may be independent of each other, but both are higher in HR tumors.

Adenocarcinoma↗
PubMed1979

Thiourea and cyanamide as inhibitors of thyroid peroxidase: the role of iodide.

Thiourea, methylmercaptoimidazole, propylthiouracil, and thiouracil are all potent inhibitors of thyroid peroxidase (TPO)-catalyzed iodination. Unlike the cyclic thioureylenes, thiourea at 5 mM has no effect on guaiacol oxidation. If iodide is added to guaiacol assays containing thiourea, enzyme activity is lost. The latter observation may be explained as follows. In the presence of iodide, the iodinating species [TPO.Ioxid], oxidizes thiourea to formamidine disulfide. This product decomposes to cyanamide at neutral pH. We have shown cyanamide to be an inhibitor of the peroxidative and iodinating functions of TPO. Studies in rats demonstrate that doses of thiourea which completely inhibit in vivo protein-bound iodine formation have no irreversible effect on TPO, as measured by guaiacol peroxidation after removal of the thyroids. The major in vivo action of cyanamide is similar to that of thiourea. The data suggest that the primary in vivo and in vitro mode of action of thiourea is the reversible Ioxid-trapping mechanism. The anomalous inhibition of guaiacol peroxidation seen in the presence of thiourea plus iodide derives from the formation of formamide disulfide, followed by its nonenzymic decomposition to cyanamide.

Animals↗
PubMed1978

Oxidation of Escherichia coli sulfhydryl components by the peroxidase-hydrogen peroxide-iodide antimicrobial system.

The chemical modification of bacterial components was studied following incubation of Escherichia coli with the peroxidase-hydrogen peroxide (H(2)O(2))-iodide (I(-)) antimicrobial system or with iodine (I(2)). The oxidation of cell sulfhydryls and the iodination of cell components were measured. Both the peroxidase system and I(2) oxidized sulfhydryls. When the I(-) concentration in the peroxidase system was greater than 100 muM, the peroxidase system and I(2) were equivalent. That is, sulfhydryl oxidation or killing per mole of H(2)O(2) equaled that per mole of I(2). These results were consistent with peroxidase-catalyzed oxidation of I(-) to yield 1 mol of I(2) per mol of H(2)O(2). Sulfhydryls were oxidized to yield sulfenic acids and free I(-). With I(-) concentrations in the range of 10 to 100 muM, the amount of sulfhydryls oxidized by the peroxidase system could exceed the amount of I(-). Because the oxidation of sulfhydryls to sulfenic acids did not consume I(-), one I(-) ion could participate in the oxidation of many sulfhydryls. With I(-) concentrations lower than 10 muM, complete oxidation of sulfhydryls was not obtained. Incorporation of I(-) into iodinated derivatives of bacterial components partly depleted the system of I(-) and limited the formation of I(2). These results indicated that antimicrobial activity was due to peroxidase-catalyzed oxidation of I(-) to I(2), followed by I(2) oxidation of cell components. There was a direct relationship between sulfhydryl oxidation and antimicrobial action. Although iodination of bacterial components accompanied sulfhydryl oxidation, the amount of I(-) incorporation was not directly related to antimicrobial action. Also, incorporation of I(-) interfered with antimicrobial action at low I(-) concentrations.

Escherichia coli↗
PubMed1977

Biosynthesis of thyroid hormone: basic and clinical aspects.

Thyroid hormone formation requires the coincident presence of peroxidase, H2O2, iodide, and acceptor protein at one anatomic locus in the cell. The peroxidase enzyme appears to be a protoporphyrin lX containing heme protein, with binding sites for both iodide and tyrosine. It is probable that both iodide and tyrosine are oxidized to free radical forms which unite to form iodotyrosine. The peroxidase is also involved through an uncertain mechanism in iodotyrosine coupling and probably in oxidation of sulfhydryl bonds in thyroglobulin. H2O2 may be supplied by microsomal NADPH-cytochrome c reductase or NADH-cytochrome b5 reductase. Other possible intracellular H2OI generating systems include monoamine oxidase and xanthine oxidase. The usual acceptor for iodide is thyroglobulin, which is currently believed to be iodinated within apical secretory vesicles at the cell border just prior to liberation into the colloid, or possibly after liberation into the colloid. Other soluble an insoluble proteins are also iodinated within the gland. The peroxidase is present in numerous cellular structures, but iodination activity occurs primarily, if not only, at the apical cell border. The controls of iodination are imperfectly known. Thyrotrophin modulation of iodide uptake, H2O2 generation, thyroglobulin synthesis, and peroxidase enzyme level obviously are the main regulations. Many of these actions are thought to involve mediation of adenyl cyclase and subsequent activation of intracellular phosphokinases. Antithyroid drugs of the thiocarbamide group are competitive inhibitors of iodination under some circumstances, but if much iodide is present, they react with the oxidized iodine intermediate and are irreversibly inactivated themselves. Clinical problems involving defective peroxidase function are among the most frequent hereditary defects of thyroid hormone formation. Recognized abnormalities include deficient peroxidase, abnormality in binding of the peroxidase apoprotein to its prosthetic group, and other less well-identified abnormalities in peroxidase structure and function. Peroxidase is typically elevated in thyroid tissue from patients with hyperthyroidism sometimes deficient in cold thyroid nodules, and frequently diminished in tissue from patients with Hashimoto's thyroiditis.

Animals↗
PubMed1977

Spatial requirement for coupling of iodotyrosine residues to form thyroid hormones.

A linear random copolymer of tyrosine and lysine and two synthetic oligopeptides containing two tyrosine residues in addition to lysine residues give thyroid hormone (thyroxine and triodothyronine) residues in good yield upon enzymatic iodination with thyroid peroxidase. These synthetic peptides may serve as simple models for thyroglobulin, the protein in which biosynthesis of the thyroid hormone takes place. For the formation of significant amounts of hormone, such model compounds must contain at least two properly spaced tyrosine residues.

Iodide Peroxidase↗
PubMed1979

Antithyroid and antiperoxidase activity of tropolone and 3-hydroxy-4-pyrone.

Tropolone (TR) and 3-hydroxy-4-pyrone were investigated for antithyroid activity following the finding that the 2-hydroxy-oxo pyridine, 3-hydroxy-4(1H)-pyridone (DHP, I), is goitrogenic. Both compounds inhibited the thyroidal uptake of radioiodine in rats and resembled the thioamide drugs in inhibiting the organic binding of iodine by the thyroid gland rather than the trapping of iodide, but were weaker binding inhibitors than 6-methyl-2-thiouracil (MeTU). Both compounds also inhibited the iodination of bovine serum albumin and thyroglobulin, catalyzed by thyroidperoxidase (TPO), lactoperoxidase (LPO), chloroperoxidase (CPO) and horseradish peroxidase (HPO) in vitro. The inhibitory effect of TR but not that of 3-hydroxy-4-pyrone was antagonized by ferrous ions. When fed to mice at levels of intake expected to produce goitre both compounds were toxic and caused severe liver damage. Thyroid enlargement was not observed in any of these feeiding experiments, but the thyroids of mice fed 0.1% TR showed moderate hyperplasia. It was concluded that both compounds are weakly goitrogenic. Hyperactivity was observed in the mice fed TR which may be associated with inhibition of catechol methyl transferase (COMT).

Animals↗
PubMed1979

Rapid conversion of carbimazole to methimazole in serum; evidence for an enzymatic mechanism.

Carbimazole (CBZ) is one of the major drugs currently used for the treatment of Graves' disease. It is a carbethoxy derivative of methimazole (MMI), originally developed in the hope of obtaining a longer acting drug than methimazole. In the present study we have demonstrated that carbimazole is rapidly converted to methimazole in vitro by serum from rats and humans, and we have obtained evidence that this conversion is enzymatic. Experiments with [35S] CBZ in rats showed that the drug is so rapidly transformed to MMI after i.v. injection (within 3 min) that very little of the unchanged drug would be expected to reach the thyroid gland. The antithyroid action of CBZ in rats, therefore, can be ascribed entirely to the MMI to which it is rapidly converted. Although no experiments were performed with human subjects in vivo, the very rapid conversion of CBZ to MMI by human serum in vitro suggests that the antithyroid action of CBZ in humans can also be attributed to MMI. The original expectation of a longer acting drug has, therefore, not been met by CBZ. On the basis of the studies reported here there appears to be no advantage in using CBZ in preference to MMI for the treatment of Graves' disease. Although the in vivo action of CBZ must be attributed to its rapid conversion to MMI, the drug does possess inherent antithyroid activity. This was shown in the present study by the finding that CBZ is as potent as MMI in blocking thyroid peroxidase-catalysed iodination of thyroglobulin.

Animals↗