Indolethylamine N-methyltransferase (INMT) is a transmethylation enzyme that utilizes the methyl donor S-adenosyl-L-methionine to transfer methyl groups to amino groups of small molecule acceptor compounds. INMT is best known for its role in the biosynthesis of N,N-Dimethyltryptamine (DMT), a psychedelic compound found in mammalian brain and other tissues. In mammals, biosynthesis of DMT is thought to occur via the double methylation of tryptamine, where INMT first catalyzes the biosynthesis of N-methyltryptamine (NMT) and then DMT. However, it is unknown whether INMT is necessary for the biosynthesis of endogenous DMT. To test this, we generated a novel INMT-knockout rat model and studied tryptamine methylation using radiometric enzyme assays, thin-layer chromatography, and ultra-high-performance liquid chromatography tandem mass spectrometry. We also studied tryptamine methylation in recombinant rat, rabbit, and human INMT. We report that brain and lung tissues from both wild type and INMT-knockout rats show equal levels of tryptamine-dependent activity, but that the enzymatic products are neither NMT nor DMT. In addition, rat INMT was not sufficient for NMT or DMT biosynthesis. These results suggest an alternative enzymatic pathway for DMT biosynthesis in rats. This work motivates the investigation of novel pathways for endogenous DMT biosynthesis in mammals.

吲哚乙胺N-甲基转移酶 (INMT) 是一种转甲基化酶，利用甲基供体S-腺苷-L-甲硫氨酸将甲基转移到小分子受体化合物的氨基上。INMT 因其在N,N-二甲基色胺 (DMT)生物合成中的作用而闻名，DMT 是一种在哺乳动物大脑和其他组织中发现的迷幻化合物。在哺乳动物中，DMT 的生物合成被认为是通过色胺的双甲基化发生的，其中 INMT 首先催化N-甲基色胺 (NMT) 的生物合成，然后催化 DMT。然而，INMT对于内源性DMT的生物合成是否是必需的尚不清楚。为了测试这一点，我们构建了一种新型 INMT 敲除大鼠模型，并使用放射性酶测定、薄层色谱和超高效液相色谱串联质谱研究了色胺甲基化。我们还研究了重组大鼠、兔和人 INMT 中的色胺甲基化。我们报告说，野生型和 INMT 敲除大鼠的脑和肺组织显示出相同水平的色胺依赖性活性，但酶产物既不是 NMT 也不是 DMT。此外，大鼠 INMT 不足以进行 NMT 或 DMT 生物合成。这些结果表明大鼠体内 DMT 生物合成存在另一种酶促途径。这项工作激发了对哺乳动物内源性 DMT 生物合成新途径的研究。