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外文期刊>The biochemical journal
>Deiodination of l-thyroxine and its activity on the oxidation in vitro of reduced nicotinamide–adenine dinucleotide by peroxidase plus hydrogen peroxide
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Deiodination of l-thyroxine and its activity on the oxidation in vitro of reduced nicotinamide–adenine dinucleotide by peroxidase plus hydrogen peroxide
pWhen l-thyroxine activates the oxidation of NADH by peroxidase+Hsub2/subOsub2/sub, little removal of phenolic-ring iodine atoms becomes apparent until most of the NADH has been oxidized, after which it increases markedly. This extensive deiodination is accompanied by loss of the ability of thyroxine to catalyse the oxidation of NADH by peroxidase+Hsub2/subOsub2/sub. The slight deiodination observed before the appearance of extensive deiodination is somewhat higher when the effect of thyroxine on NADH oxidation is greater, and lower when thyroxine has exerted a slighter effect. ICN (but not Isub2/sub or thyronine) catalyses NADH oxidation, in both the presence and the absence of peroxidase+Hsub2/subOsub2/sub: thyroxine+peroxidase+Hsub2/subOsub2/sub are thus comparable with ICN alone in their effects on NADH oxidation. The obvious conclusion from the above observation, namely that the active moiety is the halogen liberated from thyroxine (or ICN) is, however, not directly supported by some of the results obtained by measuring the degree of deiodination of thyroxine in the system. In an attempt to reconcile some apparently contradictory conclusions, it is suggested that, when thyroxine activates oxidation of NADH by peroxidase+Hsub2/subOsub2/sub, the diphenyl ether structure is undergoing cyclic deiodination and iodination. This would be accompanied by the maintenance in the reaction medium of an oxidized form of iodine, similar to that liberated by ICN, which would be the actual active moiety, until the NADH concentration becomes so low that the diphenyl ether structure is ruptured oxidatively. An alternative explanation is that thyroxine is oxidized to a form that either oxidizes NADH or loses iodine in competing reactions./p
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机译：>当l-甲状腺素通过过氧化物酶+ H 2 O 2 激活NADH的氧化作用时，直到大部分NADH具有被氧化，然后显着增加。这种广泛的脱碘作用伴随着甲状腺素催化过氧化物酶+ H 2 O 2 催化NADH氧化的能力的丧失。当甲状腺素对NADH的氧化作用较大时，在出现广泛的脱碘作用之前观察到的轻微脱碘作用较高，而当甲状腺素发挥较小作用时，观察到的轻微脱碘作用较低。在存在和不存在过氧化物酶+ H 2 O 2 的情况下，ICN（而不是I 2 或甲状腺素）催化NADH氧化：甲状腺素因此，+过氧化物酶+ H 2 O 2 与单独的ICN在对NADH氧化的影响方面具有可比性。从上述观察得出的显而易见的结论，即活性部分是从甲状腺素（或ICN）中释放出来的卤素，然而，通过测量系统中甲状腺素的去碘化程度获得的一些结果并不能直接支持这一点。为了调和一些明显矛盾的结论，建议当甲状腺素通过过氧化物酶+ H 2 O 2 激活NADH的氧化时，二苯醚结构呈环状碘化和碘化。这将伴随着反应介质中碘的氧化形式的维持，类似于由ICN释放的碘，它将是实际的活性部分，直到NADH浓度变得如此之低以致二苯醚结构被氧化破坏。另一种解释是甲状腺素被氧化成在竞争性反应中氧化NADH或失去碘的形式。
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