Nitric oxide synthase (NOS) catalyzes the conversion of l-arginine to l-citrulline and the second messenger nitric oxide. Three mechanistic pathways are proposed for the inactivation of neuronal NOS (nNOS) by (S)-2-amino-5-(2-(methylthio)acetimidamido)pentanoic acid (1): sulfide oxidation, oxidative dethiolation, and oxidative demethylation. Four possible intermediates were synthesized. All compounds were assayed with nNOS, their IC50, KI, and kinact values were obtained, and their crystal structures were determined. The identification and characterization of the products formed during inactivation provide evidence for the details of the inactivation mechanism. On the basis of these studies, the most probable mechanism for the inactivation of nNOS involves oxidative demethylation with the resulting thiol coordinating to the cofactor heme iron. Although nNOS is a heme-containing enzyme, this is the first example of a NOS that catalyzes an S-demethylation reaction; the novel mechanism of inactivation described here could be applied to the design of inactivators of other heme-dependent enzymes.

中文翻译：

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(S)-2-Amino-5-(2-(methylthio)acetimidamido)pentanoic Acid 灭活神经元一氧化氮合酶的机制

一氧化氮合酶 (NOS) 催化 L-精氨酸转化为 L-瓜氨酸和第二信使一氧化氮。(S)-2-amino-5-(2-(methylthio)acetimidamido)pentanoic acid (1) 提出了三种用于灭活神经元 NOS (nNOS) 的机制途径：硫化物氧化、氧化脱硫和氧化脱甲基。合成了四种可能的中间体。用nNOS测定所有化合物，获得它们的IC50、KI和kinact值，并确定它们的晶体结构。灭活过程中形成的产物的鉴定和表征为灭活机制的细节提供了证据。在这些研究的基础上，nNOS 失活的最可能机制涉及氧化去甲基化，产生的硫醇与辅因子血红素铁配位。尽管 nNOS 是一种含血红素的酶，但这是催化 S-去甲基化反应的 NOS 的第一个例子；这里描述的灭活的新机制可以应用于其他血红素依赖性酶的灭活剂的设计。