Burner U, Krapfenbauer G, Furtmüller P G, Regelsberger G, Obinger C
Institute of Chemistry, University of Agricultural Sciences, Vienna, Austria.
Redox Rep. 2000;5(4):185-90. doi: 10.1179/135100000101535735.
Myeloperoxidase is very susceptible to reducing radicals because the reduction potential of the ferric/ferrous redox couple is much higher compared with other peroxidases. Semiquinone radicals are known to reduce heme proteins. Therefore, the kinetics and spectra of the reactions of p-hydroquinone, 2,3-dimethylhydroquinone and 2,3,5-trimethylhydroquinone with compounds I and II were investigated using both sequential-mixing stopped-flow techniques and conventional spectrophotometric measurements. At pH 7 and 15 degrees C the rate constants for compound I reacting with p-hydroquinone, 2,3-dimethylhydroquinone and 2,3,5-trimethylhydroquinone were determined to be 5.6+/-0.4 x 10(7) M(-1)s(-1), 1.3+/-0.1 x 10(6) M(-1)s(-1) and 3.1+/-0.3 x 10(6) M(-1)s(-1), respectively. The corresponding reaction rates for compound II reduction were calculated to be 4.5+/-0.3 x 10(6) M(-1)s(-1), 1.9+/-0.1 x 10(5) M(-1)s(-1) and 4.5+/-0.2 x 10(4) M(-1)s(-1), respectively. Semiquinone radicals, produced by compounds I and II in the classical peroxidation cycle, promote compound III (oxymyeloperoxidase) formation. We could monitor formation of ferrous myeloperoxidase as well as its direct transition to compound II by addition of molecular oxygen. Formation of ferrous myeloperoxidase is shown to depend strongly on the reduction potential of the corresponding redox couple benzoquinone/semiquinone. With 2,3-dimethylhydroquinone and 2,3,5-trimethylhydroquinone as substrate, myeloperoxidase is extremely quickly trapped as compound III. These MPO-typical features could have potential in designing specific drugs which inhibit the production of hypochlorous acid and consequently attenuate inflammatory tissue damage.
髓过氧化物酶对还原自由基非常敏感，因为与其他过氧化物酶相比，铁离子/亚铁离子氧化还原对的还原电位要高得多。已知半醌自由基会还原血红素蛋白。因此，使用连续混合停流技术和传统分光光度测量法，研究了对苯二酚、2,3 - 二甲基对苯二酚和2,3,5 - 三甲基对苯二酚与化合物I和II反应的动力学和光谱。在pH 7和15摄氏度下，化合物I与对苯二酚、2,3 - 二甲基对苯二酚和2,3,5 - 三甲基对苯二酚反应的速率常数分别测定为5.6±0.4×10⁷ M⁻¹s⁻¹、1.3±0.1×10⁶ M⁻¹s⁻¹和3.1±0.3×10⁶ M⁻¹s⁻¹。化合物II还原的相应反应速率经计算分别为4.5±0.3×10⁶ M⁻¹s⁻¹、1.9±0.1×10⁵ M⁻¹s⁻¹和4.5±0.2×10⁴ M⁻¹s⁻¹。在经典过氧化循环中由化合物I和II产生的半醌自由基促进了化合物III（氧合髓过氧化物酶）的形成。通过添加分子氧，我们可以监测亚铁髓过氧化物酶的形成及其直接转变为化合物II的过程。结果表明，亚铁髓过氧化物酶的形成强烈依赖于相应氧化还原对苯醌/半醌的还原电位。以2,3 - 二甲基对苯二酚和2,3,5 - 三甲基对苯二酚为底物时，髓过氧化物酶会极快地被捕获为化合物III。这些髓过氧化物酶的典型特征在设计抑制次氯酸产生从而减轻炎症组织损伤的特定药物方面可能具有潜力。
