Chen G X, Asada K
Research Institute for Food Science, Kyoto University, Japan.
J Biol Chem. 1990 Feb 15;265(5):2775-81.
Guaiacol peroxidase from spinach catalyzes the oxidation of p-aminophenol to produce the aminophenoxy radical as the primary product which is converted further into a stable oxidation product with an absorption peak at 470 nm. The p-aminophenol radicals oxidize ascorbate (AsA) to produce monodehydroascorbate radicals. Kinetic analysis indicates that p-aminophenol radicals also oxidize monodehydroascorbate to dehydroascorbate. Incubation of AsA peroxidase from tea leaves and hydrogen peroxide with p-aminophenol, p-cresol, hydroxyurea, or hydroxylamine results in the inactivation of the enzyme. No inactivation of the enzyme was found upon incubation of the enzyme with these compounds either in the absence of hydrogen peroxide or with the stable oxidized products of these compounds. The enzyme was protected from inactivation by the inclusion of AsA in the incubation mixture. The radicals of p-aminophenol and hydroxyurea were produced by AsA peroxidase as detected by their ESR signals. These signals disappeared upon the addition of AsA, and the signal characteristic of monodehydroascorbate was found. Thus, AsA peroxidase is inactivated by the radicals of p-aminophenol, p-cresol, hydroxyurea, and hydroxylamine which are produced by the peroxidase reaction, and it is protected from inactivation by AsA via the scavenging of the radicals. Thus, these compounds are the suicide inhibitors for AsA peroxidase. Isozyme II of AsA peroxidase, which is localized in chloroplasts, is more sensitive to these compounds than isozyme I. In contrast to AsA peroxidase, guaiacol peroxidase was not affected by these various compounds, even though each was oxidized by it and the corresponding radicals were produced.
菠菜中的愈创木酚过氧化物酶催化对氨基苯酚氧化，生成氨基苯氧基自由基作为主要产物，该自由基进一步转化为在470 nm处有吸收峰的稳定氧化产物。对氨基苯酚自由基氧化抗坏血酸（AsA）生成单脱氢抗坏血酸自由基。动力学分析表明，对氨基苯酚自由基也能将单脱氢抗坏血酸氧化为脱氢抗坏血酸。将茶叶中的AsA过氧化物酶与过氧化氢、对氨基苯酚、对甲酚、羟基脲或羟胺一起孵育，会导致该酶失活。在没有过氧化氢的情况下，或者与这些化合物的稳定氧化产物一起孵育时，未发现该酶失活。在孵育混合物中加入AsA可保护该酶不被失活。通过电子自旋共振信号检测到，AsA过氧化物酶产生了对氨基苯酚和羟基脲的自由基。加入AsA后，这些信号消失，并发现了单脱氢抗坏血酸的信号特征。因此，AsA过氧化物酶会被过氧化物酶反应产生的对氨基苯酚、对甲酚、羟基脲和羟胺的自由基失活，而AsA通过清除这些自由基保护其不被失活。因此，这些化合物是AsA过氧化物酶的自杀性抑制剂。定位于叶绿体中的AsA过氧化物酶同工酶II比同工酶I对这些化合物更敏感。与AsA过氧化物酶不同，愈创木酚过氧化物酶不受这些各种化合物的影响，尽管每种化合物都会被它氧化并产生相应的自由基。
