Abstract 2-Mercapto-3-methyl-1-butanol (2M3MB) imparts an onion-like off-flavor to beer and is known to be formed from 2,3-epoxy-3-methylbutanal (EMB), which is generated in the reaction of iso-alpha acids with oxygen during the hot aeration of brewer's wort. Our previous results revealed that 2-mercapto-3-hydroxy-3-methylbutanal (2M3H3MB), formed from EMB by a nonenzymatic reaction with hydrogen sulfide, serves as the intermediate to 2M3MB. However, little is known regarding the 2M3H3MB to 2M3MB conversion process. In the present study, preparative column chromatography coupled with an enzyme assay revealed that two enzymes of Saccharomyces pastorianus, Old Yellow Enzyme 2 (Oye2p) and alcohol dehydrogenase 6 (Adh6p), are involved in the conversion process. An in vitro reaction containing these enzymes purified from recombinant Escherichia coli cells converted 2M3H3MB to 2M3MB. Furthermore, a yeast mutant with deletion of the genes encoding these two enzymes dramatically decreased 2M3MB formation. Our series of studies has therefore revealed the overall mechanism of 2M3MB formation starting from EMB through 2M3MB.

中文翻译：

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阐明啤酒中 2-Mercapto-3-Methyl-1-Butanol 的形成机制。第二部分：酵母中关键酶的鉴定

摘要 2-Mercapto-3-methyl-1-butanol (2M3MB) 赋予啤酒类似洋葱的异味，并且已知由 2,3-epoxy-3-methylbutanal (EMB) 形成，EMB 在在啤酒麦芽汁的热曝气过程中异α酸与氧气的反应。我们之前的结果表明，EMB 通过与硫化氢的非酶促反应形成的 2-mercapto-3-hydroxy-3-methylbutanal (2M3H3MB) 作为 2M3MB 的中间体。但是，对于 2M3H3MB 到 2M3MB 的转换过程知之甚少。在本研究中，制备柱色谱结合酶分析表明，酵母菌的两种酶，老黄酶 2 (Oye2p) 和醇脱氢酶 6 (Adh6p) 参与了转化过程。含有从重组大肠杆菌细胞中纯化的这些酶的体外反应将 2M3H3MB 转化为 2M3MB。此外，缺失编码这两种酶的基因的酵母突变体显着降低了 2M3MB 的形成。因此，我们的系列研究揭示了从 EMB 到 2M3MB 形成 2M3MB 的整体机制。