Korytowski W, Sarna T, Kalyanaraman B, Sealy R C
Biochim Biophys Acta. 1987 Jun 22;924(3):383-92. doi: 10.1016/0304-4165(87)90152-8.
The oxidation of four catechol(amine)s by tyrosinase has been studied by electron spin resonance and optical methods. Rates of oxygen consumption and of dopaquinone and dopachrome formation during the oxidation of dopa have been measured, and compared with rates of dopasemiquinone production measured using spin-stabilization procedures. In the presence of spin-stabilizing metal ions, production of semiquinone is approximately quantitative. Time-dependent ESR spectra obtained from dopa and dopamine show a slow regeneration of semiquinone, suggesting that a semiquinone precursor is slowly reformed. In contrast, time-dependent spectra for 4-methylcatechol and N-acetyldopamine show decay of the primary semiquinone together with buildup of a secondary semiquinone apparently derived from the corresponding 6-hydroxy-catechol(amine). Thus, catecholamines that give rise to a cyclizable quinone show a pattern of behavior that differs from those that produce a non-cyclizable quinone. These results are discussed in terms of their possible significance to melanogenesis and the toxicity of catechol(amine)s, which has been attributed to production of semiquinones and/or other oxygen radicals.
通过电子自旋共振和光学方法研究了酪氨酸酶对四种儿茶酚（胺）的氧化作用。测定了多巴氧化过程中的耗氧速率以及多巴醌和多巴色素的形成速率，并与使用自旋稳定程序测得的多巴半醌生成速率进行了比较。在存在自旋稳定金属离子的情况下，半醌的生成量大致是定量的。从多巴和多巴胺获得的随时间变化的电子自旋共振光谱显示半醌的再生缓慢，这表明半醌前体正在缓慢重新形成。相比之下，4-甲基儿茶酚和N-乙酰多巴胺的随时间变化的光谱显示初级半醌的衰减以及显然源自相应6-羟基儿茶酚（胺）的次级半醌的积累。因此，产生可环化醌的儿茶酚胺表现出与产生不可环化醌的儿茶酚胺不同的行为模式。根据这些结果对黑素生成和儿茶酚（胺）毒性的可能意义进行了讨论，儿茶酚（胺）的毒性归因于半醌和/或其他氧自由基的产生。
