Inhibition of Thyroid Peroxidase (TPO) and Lactoperoxidase (LPO) by Goitrin and Ricinine
The plant toxins, goitrin and ricinine, inhibit TPO and LPO. Goitrin (0.3 mM) completely inhibits the peroxidase-catalyzed oxidation of iodide and is nine times more potent than ricinine. Both toxins also inhibit the peroxidase-catalyzed oxidation of guaiacol, although less efficiently than iodide oxidation. Goitrin is oxidized by H2O2 in the presence, but not in the absence, of peroxidase, whereas ricinine is not oxidized. Iodide stimulates (twofold) the rate of goitrin oxidation. Spectra obtained with mixtures of LPO, H2O2, and goitrin indicate that LPOoxid oxidizes goitrin and is converted back to native LPO. Thus, both LPOoxid and LPO-Ioxid oxidize goitrin but LPO-Ioxid is more effective. Because of their well known toxicity, neither of these toxins derived from Brassicae plants (goitrin) and castor beans (ricinine) is considered a serious dietary problem.
KeywordsGlucose Oxidase Castor Bean Potassium Iodide Thyroid Peroxidase Plant Toxin
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