It is theoretically plausible that thiazolium mesomerizes to congeners other than carbene in a low effective dielectric binding site; especially given the energetics and uneven electronegativity of carbene groups. However, such a phenomenon has never been reported. Nine crystal structures of transketolase obtained from Pichia stipitis (TKps) are reported with subatomic resolution, where thiazolium displays an extraordinary ring‐bending effect. The bent thiazolium congeners correlate with non‐Kekulé diradicals because there is no gain or loss of electrons. In conjunction with biophysical and biochemical analyses, it is concluded that ring bending is a result of tautomerization of thiazolium with its non‐ Kekulé diradicals, exclusively in the binding site of TKps. The chemophysical properties of these thiazolium mesomers may account for the great variety of reactivities carried out by thiamine–diphosphate‐containing (ThDP) enzymes. The stability of ThDP in living systems can be regulated by the levels of substrates, and hydration and dehydration, as well as diradical‐mediated oxidative degradation.

中文翻译：

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噻唑对吡氏毕赤酵母转酮酶中非Kekulé自由基的介观作用

从理论上讲，在低有效介电结合位点上，噻唑鎓会异构化为除卡宾外的同类物。特别是考虑到卡宾基团的能量和不均匀的负电性。但是，这种现象从未被报道过。树干毕赤酵母中转酮醇酶的九种晶体结构（TKps）以亚原子分辨率报道，其中噻唑鎓显示出非凡的环弯曲效应。弯曲的噻唑鎓同类物与非Kekulé双自由基相关，因为没有电子的获得或损失。结合生物物理和生化分析，得出的结论是，环弯曲是噻唑与非Kekulé双自由基的互变异构化的结果，仅在TKps的结合位点。这些噻唑鎓类液晶异构体的化学物理性质可能解释了含硫胺素-二磷酸（ThDP）酶的多种反应性。ThDP在生命系统中的稳定性可以通过底物的水平，水合和脱水以及双基介导的氧化降解来调节。