Human salivary peroxidase-catalyzed oxidation of nitrite and nitration of salivary components 4-hydroxyphenylacetic acid and proteins

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• 作者：Takahama ; Umeo ; Hirota ; Sachiko ; Nishioka ; Takahiro ; Oniki ; Takayuki
• 关键词：DTNB ; 5 ; 5&prime ; -dithio-bis(2-nitrobenzoic acid) ; HPA ; 4-hydroxyphenylacetic acid ; NO₂HPA ; 4-hydroxy-3-nitrophenylacetic acid ; SPX ; salivary peroxidase ; TNB ; 5-thio-2-nitrobenzoic acid ; Human saliva ; 4-Hydroxyphenylacetic acid ; Nitration ; Nitri
• 刊名：Archives of Oral Biology
• 出版年：2003
• 期刊代码：25_00039969
• 类别：med
• 出版时间：October, 2003
• 卷：48
• 期：10
• 页码：679-690
• 文件大小：273 K

摘要

Human saliva contains high activities of peroxidase and high concentrations of nitrite (about 0.2mM in average). If H₂O₂ is provided by bacteria and leukocytes in the oral cavity, peroxidase-dependent formation of reactive nitrogen species, which can nitrate phenolics like 4-hydroxyphenylacetic acid (HPA) and tyrosine residues in salivary proteins, is possible. H₂O₂-dependent oxidation of nitrite and H₂O₂-dependent nitration of HPA were observed in dialyzed saliva and by partially purified salivary peroxidase (SPX). The nitration was inhibited by a physiological electron donor to salivary peroxidase, SCN⁻. When concentrations of H₂O₂ and nitrite were increased, nitration of HPA was also observed in control (non-dialyzed) saliva. In addition, H₂O₂-dependent nitration of tyrosine residues in salivary proteins was observed in dialyzed saliva as an increase in absorbance around 420nm at pH 7.2. Kinetic studies of the increase in absorbance indicated that sulfhydryl groups in salivary proteins as well as glutathione, ascorbate, urate and SCN⁻ could inhibit the nitration. Since the nitration of proteins can lead to impairment of their functions, it is discussed how the oral cavity is protected from the damages caused by reactive nitrogen species under normal conditions and also discussed that reactive nitrogen species generated by the H₂O₂/nitrite/peroxidase system can participate in the host defence mechanism in the oral cavity.