Fetzner S
Mikrobiologie, Fachbereich 7, Carl von Ossietzky Universität Oldenburg, P.O. Box 2503, 26111 Oldenburg, Germany.
Naturwissenschaften. 2000 Feb;87(2):59-69. doi: 10.1007/s001140050011.
Many N-heteroaromatic compounds are utilized by micro-organisms as a source of carbon (and nitrogen) and energy. The aerobic bacterial degradation of these growth substrates frequently involves several hydroxylation steps and subsequent dioxygenolytic cleavage of (di)hydroxy-substituted heteroaromatic intermediates to aliphatic metabolites which finally are channeled into central metabolic pathways. As a rule, the initial bacterial hydroxylation of a N-heteroaromatic compound is catalyzed by a molybdenum hydroxylase, which uses a water molecule as source of the incorporated oxygen. The enzyme's redox-active centers - the active site molybdenum ion coordinated to a distinct pyranopterin cofactor, two different [2Fe2S] centers, and in most cases, flavin adenine dinucleotide - transfer electrons from the N-heterocyclic substrate to an electron acceptor, which for many molybdenum hydroxylases is still unknown. Ring-opening 2,4-dioxygenases involved in the bacterial degradation of quinaldine and 1H-4-oxoquinoline catalyze the cleavage of two carbon-carbon bonds with concomitant formation of carbon monoxide. Since they contain neither a metal center nor an organic cofactor, and since they do not show any sequence similarity to known oxygenases, these unique dioxygenases form a separate enzyme family. Quite surprisingly, however, they appear to be structurally and mechanistically related to enzymes of the alpha/beta hydrolase fold superfamily. Microbial enzymes are a great resource for biotechnological applications. Microbial strains or their enzymes may be used for degradative (bioremediation) or synthetic (biotransformation) purposes. Modern bioremediation or biotransformation strategies may even involve microbial catalysts or strains designed by protein engineering or pathway engineering. Prerequisite for developing such modern tools of biotechnology is a comprehensive understanding of microbial metabolic pathways, of the structure and function of enzymes, and of the molecular mechanisms of biocatalysis.
许多含氮杂环化合物被微生物用作碳（和氮）源及能源。这些生长底物的需氧细菌降解通常涉及多个羟基化步骤，随后是（二）羟基取代的杂环芳烃中间体的双加氧裂解，生成脂肪族代谢物，最终进入中心代谢途径。通常，含氮杂环化合物的初始细菌羟基化由钼羟化酶催化，该酶利用水分子作为掺入氧的来源。该酶的氧化还原活性中心——与独特的吡喃蝶呤辅因子、两个不同的[2Fe2S]中心配位的活性位点钼离子，以及在大多数情况下的黄素腺嘌呤二核苷酸——将电子从含氮杂环底物转移到电子受体，而对于许多钼羟化酶来说，该电子受体仍不清楚。参与喹哪啶和1H - 4 - 氧代喹啉细菌降解的开环2,4 - 双加氧酶催化两条碳 - 碳键的裂解，同时生成一氧化碳。由于它们既不含有金属中心也不含有有机辅因子，并且与已知的加氧酶没有任何序列相似性，这些独特的双加氧酶形成了一个单独的酶家族。然而，非常令人惊讶的是，它们在结构和机制上似乎与α/β水解酶折叠超家族的酶相关。微生物酶是生物技术应用的重要资源。微生物菌株或其酶可用于降解（生物修复）或合成（生物转化）目的。现代生物修复或生物转化策略甚至可能涉及通过蛋白质工程或途径工程设计的微生物催化剂或菌株。开发生物技术这种现代工具的前提是全面了解微生物代谢途径、酶的结构和功能以及生物催化的分子机制。
