Spectral studies with lactoperoxidase and thyroid peroxidase: interconversions between native enzyme, compound II, and compound III.
Spectral studies with lactoperoxidase and thyroid peroxidase: interconversions between native enzyme, compound II, and compound III.
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DOI：
10.1016/0003-9861(88)90309-8
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发表时间：
1988-08
影响因子：
3.9
通讯作者：
H. Kohler;A. Taurog;H. Dunford
中科院分区：
文献类型：
--
作者：
H. Kohler;A. Taurog;H. Dunford
记录乳过氧化物酶和甲状腺过氧化物酶的天然酶、化合物II和化合物III在可见光(650-450 nm)和Soret (450-380 nm)区域的光谱扫描。每种酶的化合物 II (1.7 μm) 是通过添加稍微过量的 H2O2 (6 μm) 来制备的，而化合物 III 则是通过添加大量过量的 H2O2 (200 μm) 来制备。这些化合物形成后，观察到它们在没有外源供体的情况下缓慢地重新转化为天然酶。化合物III返回天然酶的途径涉及作为中间体的化合物II。化合物III向天然酶的重新转化伴随着H 2 O 2 的消失和O 2 的产生，每消失2 mol H 2 O 2 大约形成1 mol O 2 。提出了一个方案来解释这些观察结果，涉及亚铁酶的中间形成。根据该方案，化合物 III 参与有效地将 H2O2 转化为 O2 的反应循环。碘化物显着影响乳过氧化物酶和甲状腺过氧化物酶的天然酶、化合物II和化合物III之间的相互转化。当乳过氧化物酶或甲状腺过氧化物酶用6μmH2O2处理时，低浓度的碘化物(4μm)完全阻断了化合物II的形成。当酶用 200 μmH2O2 处理时，同样低浓度的碘化物完全阻止了化合物 III 的形成，并在很大程度上阻止了在没有碘化物的情况下发生的酶降解。碘化物的这些作用很容易解释为：(i) 化合物 I 将碘化物双电子氧化为次碘酸盐，绕过中间体化合物 II；以及 (ii) 化合物 I 与碘化物反应中形成的次碘酸盐将 H2O2 快速氧化为 O2。
Spectral scans in both the visible (650-450 nm) and the Soret (450-380 nm) regions were recorded for the native enzyme, Compound II, and Compound III of lactoperoxidase and thyroid peroxidase. Compound II for each enzyme (1.7 μm) was prepared by adding a slight excess of H2O2(6 μm), whereas Compound III was prepared by adding a large excess of H2O2(200 μm). After these compounds had been formed it was observed that they were slowly reconverted to the native enzyme in the absence of exogenous donors. The pathway of Compound III back to the native enzyme involved Compound II as an intermediate. Reconversion of Compound III to native enzyme was accompanied by the disappearance of H2O2and generation of O2, with approximately 1 mol of O2formed for each 2 mol of H2O2that disappeared. A scheme is proposed to explain these observations, involving intermediate formation of the ferrous enzyme. According to the scheme, Compound III participates in a reaction cycle that effectively converts H2O2to O2. Iodide markedly affected the interconversions between native enzyme, Compound II, and Compound III for lactoperoxidase and thyroid peroxidase. A low concentration of iodide (4 μm) completely blocked the formation of Compound II when lactoperoxidase or thyroid peroxidase was treated with 6 μmH2O2. When the enzymes were treated with 200 μmH2O2, the same low concentration of iodide completely blocked the formation of Compound III and largely prevented the enzyme degradation that otherwise occurred in the absence of iodide. These effects of iodide are readily explained by (i) the two-electron oxidation of iodide to hypoiodite by Compound I, which bypasses Compound II as an intermediate, and (ii) the rapid oxidation of H2O2to O2by the hypoiodite formed in the reaction between Compound I and iodide.