Nakamura M, Yamazaki I, Ohtaki S
Biophysics Division, Hokkaido University.
J Biochem. 1990 Nov;108(5):804-10. doi: 10.1093/oxfordjournals.jbchem.a123284.
Iodothyronines induced catalatic (H2O2-decomposing) activity of thyroid peroxidase and lactoperoxidase, the effect increasing in the order of thyroxine (T4) greater than triiodothyronine (T3) greater than diiodothyronine (T2). The iodothyronines served as electron donors in the peroxidase reactions, and during the reactions the catalytic intermediate of thyroid peroxidase was confirmed to be Compound II for T4 and Compound I for T3 and T2 and from the Soret absorption spectra obtained by stopped-flow measurements. Rate constants for the reactions between T4 and Compound II, T3 and Compound I, and T2 and Compound I were estimated at 1.9 x 10(5), 1.3 x 10(6), and 7.1 x 10(5) M-1.s-1, respectively. Unlike the case of thyroid peroxidase, the catalytic intermediate of lactoperoxidase observed during the oxidation of iodothyronines was invariably Compound II. From these and other data it was concluded that thyroid peroxidase catalyzed one-electron oxidation of T4 and two-electron oxidations of T2 and T3 while lactoperoxidase catalyzed exclusively one-electron oxidation of the iodothyronines. Iodide was released during the enzymatic oxidation of iodothyronines, irrespective of the mechanism of one-electron and two-electron oxidations. The amount of released iodide increased in the order of T4 greater than T3 greater than T2. The iodothyronines-induced catalatic activity of these peroxidases was ascribable to the release of iodide, but it was also found that the iodide-enhanced catalatic activity was stimulated by iodothyronines. In this case the effect of iodothyronines was greater in the order of T2 greater than T3 greater than T4, which was consistent with the order of iodothyronine activation for the iodinium cation transfer from enzyme to acceptor.
甲状腺原氨酸可诱导甲状腺过氧化物酶和乳过氧化物酶的过氧化氢酶（分解H2O2）活性，其效应按甲状腺素（T4）大于三碘甲状腺原氨酸（T3）大于二碘甲状腺原氨酸（T2）的顺序增强。甲状腺原氨酸在过氧化物酶反应中作为电子供体，并且在反应过程中，通过停流测量获得的Soret吸收光谱证实，甲状腺过氧化物酶的催化中间体对于T4是化合物II，对于T3和T2是化合物I。T4与化合物II、T3与化合物I以及T2与化合物I之间反应的速率常数分别估计为1.9×10⁵、1.3×10⁶和7.1×10⁵ M⁻¹·s⁻¹。与甲状腺过氧化物酶的情况不同，在甲状腺原氨酸氧化过程中观察到的乳过氧化物酶的催化中间体始终是化合物II。根据这些及其他数据得出结论，甲状腺过氧化物酶催化T4的单电子氧化以及T2和T3的双电子氧化，而乳过氧化物酶仅催化甲状腺原氨酸的单电子氧化。在甲状腺原氨酸的酶促氧化过程中会释放碘离子，无论单电子和双电子氧化的机制如何。释放的碘离子量按T4大于T3大于T2的顺序增加。这些过氧化物酶的甲状腺原氨酸诱导的过氧化氢酶活性归因于碘离子的释放，但还发现碘离子增强的过氧化氢酶活性受到甲状腺原氨酸的刺激。在这种情况下，甲状腺原氨酸的效应按T2大于T3大于T4的顺序更大，这与碘原阳离子从酶转移到受体的甲状腺原氨酸活化顺序一致。
