Itoh N, Izumi Y, Yamada H
J Biol Chem. 1987 Sep 5;262(25):11982-7.
The properties of the nonheme iron of bromoperoxidase from Corallina pilulifera were studied. The enzyme lost its activity when reduced with formamidine-sulfinic acid and recovered it when oxidized by air. Incubation of the enzyme with ferric or ferrous ion-chelating agents indicated that its nonheme iron was ferric. Analyses of circular dichroism and proton NMR spectra suggested that the ferric ion tightly bound to cysteine, histidine, or tyrosine residues of the enzyme. The enzyme catalyzed Br--dependent catalase reactions to yield 1 mol of O2 from 2 mol of H2O2. No O2 evolution was observed when bromination reaction of monochlorodimedone occurred. From these results, together with previous knowledge of this enzyme, it was concluded that it activated bromide anion (Br-) to bromonium cation (Br+) using one molecule of H2O2, and this Br+OH- formed at the active site then decomposed another H2O2 to yield O2 in the absence of halogen acceptors (substrate). When substrate was present in the reaction mixture, it and H2O2 competitively reacted with the reaction intermediate (Br+OH-) to give brominated products.
对海萝溴过氧化物酶的非血红素铁的性质进行了研究。该酶用甲脒亚磺酸还原后失去活性，经空气氧化后恢复活性。用铁离子或亚铁离子螯合剂孵育该酶表明其非血红素铁为三价铁。圆二色性和质子核磁共振谱分析表明，三价铁离子与该酶的半胱氨酸、组氨酸或酪氨酸残基紧密结合。该酶催化依赖溴离子的过氧化氢酶反应，从2摩尔过氧化氢产生1摩尔氧气。当一氯二甲基酮发生溴化反应时，未观察到氧气释放。根据这些结果，结合此前对该酶的了解，得出结论：它利用一分子过氧化氢将溴离子（Br-）激活为溴鎓阳离子（Br+），在没有卤素受体（底物）的情况下，在活性位点形成的这种Br+OH-然后分解另一个过氧化氢以产生氧气。当反应混合物中存在底物时，它与过氧化氢与反应中间体（Br+OH-）发生竞争性反应，生成溴化产物。
