Enzymes involved in the anaerobic oxidation of n-alkanes: from methane to long-chain paraffins.
Enzymes involved in the anaerobic oxidation of n-alkanes: from methane to long-chain paraffins.
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DOI：
10.3389/fmicb.2013.00089
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发表时间：
2013
影响因子：
5.2
通讯作者：
Callaghan AV
中科院分区：
文献类型：
--
作者：
Callaghan AV
厌氧微生物在甲烷和非甲烷烷烃的生物地球化学循环中起着关键作用。迄今为止，似乎至少有三种提议的厌氧甲烷氧化（AOM）机制。第一种途径是由古细菌厌氧甲烷氧化剂和硫酸盐还原菌（SRB）通过“反向甲烷生成”联合介导，并由甲基辅酶M还原酶的同源物催化。第二种途径也是由厌氧甲烷氧化剂和SRB介导的，其中古细菌成员催化甲烷氧化和硫酸盐还原，零价硫是关键中间体。第三种AOM机制是一种亚硝酸盐依赖的“有氧内”途径，描述了反硝化细菌“候选甲基细菌”。“假设AOM是通过亚硝酸盐还原为一氧化氮，然后两个一氧化氮分子转化为二氮和分子氧来进行的。”后者可用于通过颗粒甲烷单加氧酶使甲烷功能化。对于非甲烷烷烃，似乎也有新的活化机制。描述得最好的途径是通过假定的甘酰基自由基酶，烷基琥珀酸合酶（也称为甲基烷基琥珀酸合酶），在富马酸的双键上加成非甲烷烷烃，形成烷基取代琥珀酸盐。其他提出的机制包括通过乙苯脱氢酶样酶的厌氧羟基化作用和类似于“甲基irabilis oxyfera”的“有氧”反硝化途径。
Anaerobic microorganisms play key roles in the biogeochemical cycling of methane and non-methane alkanes. To date, there appear to be at least three proposed mechanisms of anaerobic methane oxidation (AOM). The first pathway is mediated by consortia of archaeal anaerobic methane oxidizers and sulfate-reducing bacteria (SRB) via “reverse methanogenesis” and is catalyzed by a homolog of methyl-coenzyme M reductase. The second pathway is also mediated by anaerobic methane oxidizers and SRB, wherein the archaeal members catalyze both methane oxidation and sulfate reduction and zero-valent sulfur is a key intermediate. The third AOM mechanism is a nitrite-dependent, “intra-aerobic” pathway described for the denitrifying bacterium, ‘Candidatus Methylomirabilis oxyfera.’ It is hypothesized that AOM proceeds via reduction of nitrite to nitric oxide, followed by the conversion of two nitric oxide molecules to dinitrogen and molecular oxygen. The latter can be used to functionalize the methane via a particulate methane monooxygenase. With respect to non-methane alkanes, there also appear to be novel mechanisms of activation. The most well-described pathway is the addition of non-methane alkanes across the double bond of fumarate to form alkyl-substituted succinates via the putative glycyl radical enzyme, alkylsuccinate synthase (also known as methylalkylsuccinate synthase). Other proposed mechanisms include anaerobic hydroxylation via ethylbenzene dehydrogenase-like enzymes and an “intra-aerobic” denitrification pathway similar to that described for ‘Methylomirabilis oxyfera.’
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