Potential Energy Surface for Anaerobic Oxidation of Methane via Fumarate Addition
Potential Energy Surface for Anaerobic Oxidation of Methane via Fumarate Addition
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DOI：
10.1021/es3009503
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发表时间：
2012-08-07
影响因子：
11.4
通讯作者：
Nanny, Mark A.
中科院分区：
文献类型：
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作者：
Beasley, Keisha K.;Nanny, Mark A.
微生物介导的甲烷厌氧氧化(AOM)是全球甲烷循环中的一个重要汇，但其氧化机制和微生物还不完全清楚。利用量子化学计算，研究了富马酸与甲烷的加成反应，以确定这是否可能是AOM的一种能量上可行的机理。建立了初始反应的势能面(PES)，结果表明反应是放热的，计算的总能量变化在-9.8~-11.2千卡/摩尔之间。甲烷与富马酸的加成反应在反应物表面的最高点，在反应物上方25.0-25.3千卡/摩尔。在所考虑的富马酸盐的三种可能的分子构型中，对甲烷加成反应的空间位阻最小的一种产生最大的能量增益。虽然11.2千卡/摩尔可以在能量有限的条件下支持生长，但酶是否能调节25千卡/摩尔的能量障碍尚不清楚。这些计算的能量提供了可能是经历富马酸加成反应最不活跃的底物之一的值，使甲烷成为定义由含有甘氨酸基的酶激活的反应中生长的能量障碍和最低能量要求的限制的模型底物。
Microbially mediated anaerobic oxidation of methane (AOM) is an important sink in the global methane cycle, but the mechanism and microorganisms responsible for this oxidation are not fully known. Using quantum chemical calculations, fumarate addition to methane was examined to determine if it could be an energetically feasible mechanism for AOM. A potential energy surface (PES) for the initial reaction was created and the results suggest the reaction is exothermic, with a calculated overall energy change between -9.8 and -11.2 kcal/mol. The addition of methane to fumarate is calculated to be the highest point on the surface, 25.0-25.3 kcal/mol above the reactants. Of the three possible molecular configurations of fumarate considered, the one that presents the least steric obstacles to the addition reaction with methane yields the greatest energy gain. While 11.2 kcal/mol may support growth under energy limited conditions it is unknown if enzymes can mediate an energetic barrier of 25 kcal/mol. These calculated energies provide values for what could be one of the least reactive substrates to undergo fumarate addition, making methane a model substrate in defining the limits of energy barriers and minimal energy requirements for growth in reactions activated by glycyl radical-containing enzymes.