2,5-Dihydroxypridine dioxygenase (NicX) catalyzes an aromatic N-heterocylic ring opening. We renew reaction mechanisms of NicX and discover a competitive dioxetane pathway. Although the initial steps involve single-electron transfer from 2,5-hydroxypyridine (DHP) to dioxygen in both the lactone and dioxetane pathways, the ring-opening potential energy surface of the dioxetane pathway was calculated to be more favored. Energetic span (δE) of the lactone pathway was calculated to be 16.2 kcal/mol for the aromatic ring-opening step, higher by 9.4 kcal/mol than that of the dioxetane pathway. Moreover, the reactivity and pre-reaction state analyses suggest that DHP prefers a monoanionic form, or a neutral form upon proton shuttling of H105, rather than a dianionic form. Our results indicate that the 2-His-1-carboxylate-1-serine iron enzyme catalyzes the N-heterocylic aromatic ring opening via the preferential dioxetane pathway, affording a missing piece in the understanding of non-heme iron-enzyme chemistry.

2,5-二羟基吡啶双加氧酶 (NicX) 催化芳香N-杂环开环。我们更新了 NicX 的反应机制并发现了竞争性二氧杂环丁烷途径。尽管最初的步骤涉及在内酯和二氧杂环丁烷途径中从 2,5-羟基吡啶 (DHP) 到双氧的单电子转移，但经计算，二氧杂环丁烷途径的开环势能面更受青睐。经计算，芳族开环步骤的内酯途径的能量跨度 (δE) 为 16.2 kcal/mol，比二氧杂环丁烷途径高 9.4 kcal/mol。此外，反应性和反应前状态分析表明，DHP 在 H105 的质子穿梭时更喜欢单阴离子形式或中性形式，而不是双阴离子形式。我们的结果表明 2-His-1-carboxylate-1-serine 铁酶催化N-通过优先二氧杂环丁烷途径打开的杂环芳香环，为理解非血红素铁酶化学提供了一个缺失的部分。