Metodiewa D, Reszka K, Dunford H B
Department of Chemistry, University of Alberta, Edmonton, Canada.
Arch Biochem Biophys. 1989 Nov 1;274(2):601-8. doi: 10.1016/0003-9861(89)90475-x.
The reactions of native lactoperoxidase and its compound II with two substituted catechols have been investigated by ESR spin stabilization and spin trapping and by rapid scan and conventional spectrophotometric techniques. The catechols are Dopa methyl ester (dihydroxyphenylalanine methyl ester) and 6-hydroxy-Dopa (trihydroxyphenylalanine). o-Semiquinone radicals are formed in the anaerobic reaction of Dopa methyl ester with hydrogen peroxide catalyzed by native lactoperoxidase. The comparable anaerobic reaction of 6-hydroxy-Dopa appears to produce hydroxyl radicals in an unusual reaction. Compound II is reduced back to native lactoperoxidase by both catechols. The reaction between Dopa methyl ester and compound II undergoes an oscillation. The results on the overall lactoperoxidase cycle indicate two successive one-electron reductions of the peroxidase intermediates back to the native enzyme. The resulting free radical formation of o- and p-semiquinones and subsequent formation of stable quinones and Dopachromes is dependent upon the stereochemical arrangement of the catechol hydroxyl groups.
通过电子自旋共振（ESR）自旋稳定和自旋捕获以及快速扫描和传统分光光度技术，研究了天然乳过氧化物酶及其化合物II与两种取代儿茶酚的反应。这两种儿茶酚分别是多巴甲酯（二羟基苯丙氨酸甲酯）和6-羟基多巴（三羟基苯丙氨酸）。在天然乳过氧化物酶催化的多巴甲酯与过氧化氢的厌氧反应中形成邻半醌自由基。6-羟基多巴的类似厌氧反应似乎在一个不寻常的反应中产生羟基自由基。两种儿茶酚都能将化合物II还原回天然乳过氧化物酶。多巴甲酯与化合物II之间的反应会发生振荡。关于整个乳过氧化物酶循环的结果表明，过氧化物酶中间体连续两次单电子还原回到天然酶。由此产生的邻醌和对醌自由基的形成以及随后稳定醌和多巴色素的形成取决于儿茶酚羟基的立体化学排列。
