Laboratoire de Chimie et Biochimie Pharmacologiques et Toxicologiques, UMR 8601 CNRS, Université Paris Descartes, 45 rue des Saints Pères, 75270 Paris Cedex 06, France.
Arch Biochem Biophys. 2010 Oct 1;502(1):74-80. doi: 10.1016/j.abb.2010.07.002. Epub 2010 Jul 6.
Tris(p-carboxyltetrathiaaryl)methyl radicals (TAM*) are good EPR probes for measurement of dioxygen concentration in biological systems and for EPR imaging. It has been previously reported that these radicals are efficiently oxidized by superoxide, O2*(-), or alkylperoxyl radicals, ROO*, and by liver microsomes via an oxidative decarboxylation mechanism leading to the corresponding quinone-methides (QM). This article shows that peroxidases, such as horseradish peroxidase (HRP), lactoperoxidase (LPO) and prostaglandin synthase (PGHS), and other hemeproteins, such as methemoglobin (metHb), metmyoglobin (metMb) and catalase, also efficiently catalyze the oxidation of TAM* radicals to QM by H2O2 or alkylhydroperoxides. These reactions involve the intermediate formation of the corresponding cations TAM(+) that have also been cleanly generated by K2Ir(IV)Cl6 and characterized by UV-Visible spectroscopy and mass spectrometry, and through their reactions with ascorbate or H2O2. Labelling experiments on HRP-catalyzed oxidation of TAM* to QM using H2(18)O or (18)O2 in the presence of glucose and glucose oxidase (GOX) showed that the oxygen atom incorporated into QM came both from O2 and from H2O. Mechanisms for these reactions in agreement with those data were proposed. Oxidative decarboxylation of TAM* to QM is a new reaction catalyzed by peroxidases. Such reactions should be considered when using TAM* as EPR oximetry probes in vivo or in vitro in complex biological media.
三（对羧基苯）甲基自由基（TAM*）是测量生物体系中氧浓度和进行电子顺磁共振成像的良好 EPR 探针。此前有报道称，这些自由基可被超氧自由基（O2*(-)）、烷过氧自由基（ROO*）以及通过氧化脱羧机制由肝微粒体有效地氧化，导致相应的醌-亚甲基（QM）。本文表明，过氧化物酶，如辣根过氧化物酶（HRP）、乳过氧化物酶（LPO）和前列腺素合酶（PGHS），以及其他血红素蛋白，如高铁血红蛋白（metHb）、高铁肌红蛋白（metMb）和过氧化氢酶，也能有效地催化 TAM* 自由基被 H2O2 或烷基过氧化物氧化为 QM。这些反应涉及到相应的阳离子 TAM(+)的中间形成，TAM(+)也已通过 K2Ir(IV)Cl6 被干净地生成，并通过紫外-可见光谱和质谱法以及通过与抗坏血酸或 H2O2 的反应进行了表征。在葡萄糖和葡萄糖氧化酶（GOX）存在下，使用 H2(18)O 或 (18)O2 对 HRP 催化 TAM氧化为 QM 的标记实验表明，掺入 QM 的氧原子既来自 O2，也来自 H2O。提出了与这些数据相符的这些反应的机制。TAM氧化脱羧生成 QM 是过氧化物酶催化的新反应。在复杂的生物介质中体内或体外将 TAM*用作 EPR 血氧探针时，应考虑这些反应。
