Biosynthesis Studies of Branched-Chain Amino Acids by Methanogenic Bacteria

乙酰羟基酸合成酶(AHAS)是支链氨基酸生物合成途径中的关键调节酶。由于这些氨基酸约占活组织中蛋白质干重的25%，这一途径在许多微生物和植物中具有定量意义。产甲烷的古细菌甲烷球菌的AHAs正在用标准技术提纯，并测定其化学和物理性质。这种酶的基因(S)正在克隆中，并开始测序。这项研究解决了一些主要问题。古细菌中的合成代谢酶与真细菌和真核生物的酶同源吗？古细菌AHAs是否与分解代谢途径中发现的任何丙酮酸利用酶同源，包括来自大肠杆菌的丙酮酸氧化酶？来自不同来源的AHASs中的黄素和除草剂结合位点是否保守？产甲烷菌是一个重要的经济类群属于第三大生命王国，古细菌。它们催化有机物厌氧分解的最后一步，其中95%的燃烧能量保存在形成的甲烷中。复杂的生物聚合物可以转化为甲烷，甲烷是一种已经得到广泛使用的清洁燃料。因此，该发酵在废物处理中具有很大的开发潜力。此外，甲烷是大气中第二丰富的含碳气体。在过去的几百年里，它的浓度一直在增加，可能会导致温室效应和全球变暖。因此，这些微生物与我们这个星球的主要全球进程密切相关。这些关于产甲烷菌生理和调控的研究将有助于将其开发为有用的目的，并有助于衡量环境做法。

Acetohydroxy acid synthase (AHAS) is a key regulatory enzyme in the pathway of branched-chain amino acid biosynthesis. Because these amino acids constitute about 25% of the dry weight of protein in living tissue, this pathway is of quantitative significance in many microorganisms and plants. The AHAS from a methane-producing archaebacterium, Methanococcus aeolicus, is being purified by standard techniques, and its chemical and physical properties determined. The gene(s) for this enzyme is being cloned and DNA sequencing begun. A number of major questions are addressed by this research. Are anabolic enzymes in archaebacteria homologous to the eubacterial and eucaryotic enzymes? Is the archaebacterial AHAS homologous to any pyruvate-utilizing enzymes found in catabolic pathways including the pyruvate oxidase from Escherichia coli? Are the flavin and herbicide binding sites conserved in AHASs from diverse origins?%%% Methanogenic bacteria are an economically important group belonging to the third major kingdom of life, the archaebacteria. They catalyze the last step in the anaerobic decomposition of organic matter where 95% of the combustion energy is conserved in the methane formed. Complex biological polymers can be converted to methane, a clean fuel already in wide use. Therefore, there is great potential for exploitation of this fermentation in waste treatment. Furthermore, methane is the second most abundant carbon- containing gas in the atmosphere. Its concentration has been increasing for the last several hundred years and may contribute to the greenhouse effect and global warming. Thus these microorganisms are intimately associated with major global processes of our planet. These studies on methanogen physiology and regulation will facilitate their exploitation for useful purposes and help gauge environmental practices.***//