ヒト耳下腺唾液のIodide Peroxidaseに関する研究

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タイトル別名
  • Studies on Iodide Peroxidase in Human Parotid Saliva
  • ヒト ジカセン ダエキ ノ Iodide Peroxidase ニカンスルケン
  • Iodination of Tyrosine Mediated by Salivary Iodide Peroxidase
  • 唾液Iodide PeroxidaseのTyrosineへのIodination

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Recently we demonstrated the presence of iodide peroxidase (SPO) activity in human parotid and sublingual-submaxillary saliva, and indicated that the iodide-H2O2-SPO system contributes to antibacterial activity of the saliva. The purpose of this paper is to evaluate the ability of SPO to catalyze both the oxidation of iodide and iodination of tyrosine.<BR>SPO was purified from 13 liters of human parotid saliva by procedures of DEAE-cellulose column chromatography, CM-cellulose column chromatography, gel filtration on Sephadex G-200 and ammonium sulfate fractionation. The purified enzyme had a ratio of absorbancy (412nm/280nm) of 0.89. For spectral analysis of iodide oxidation, the reaction mixture contained potassium iodide (KI), H2O2 and purified SPO in acetate buffer, pH3.6. The reaction was started by adding H2O2. Absorption maxima were observed at 290, 350 and 460nm. It is well known the absorbance at 290 and 350nm are attributable, to I3- and I2 absorbance at 460nm. When an excess of peroxide was added to the reaction mixture, the 290- and 350- nm absorbance disappeared and an increase in the absorbance at 460nm was observed, indicating that SPO catalyzed the total oxidation of I- converted to I2.<BR>SPO catalysis of iodination was also studied using L-tyrosine as substrate. When peroxide was added to the reaction mixture containing KI, L-tyrosine and SPO in acetate buffer, pH 3.6, an increase in absorbance at 290nm which was attributable to monoiodotyrosine was observed. Similar results were obtained in the case in which KI in the reaction mixture was replaced with I2. As SPO was deleted from the mixture, the increase in absorbance was very slight at pH3.6.<BR>From these spectral experiments, SPO was shown to catalyze both oxidation of iodide and iodination of tyrosine. Lactoperoxidase and horseradish peroxidase were also subjected to spectal analysis for comparison with SPO. The turnover numbers of SPO for iodide oxidation and for iodination of tyrosine were both greater than those of lactoperoxidase and of horseradish peroxidase.

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