Physiology, biochemistry, and specific inhibitors of CH4, NH4+, and CO oxidation by methanotrophs and nitrifiers
Physiology, biochemistry, and specific inhibitors of CH4, NH4+, and CO oxidation by methanotrophs and nitrifiers
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DOI：
10.1128/mr.53.1.68-84.1989
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发表时间：
1989-03
期刊：
影响因子：
--
通讯作者：
C. Bédard;R. Knowles
中科院分区：
文献类型：
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作者：
C. Bédard;R. Knowles
氨氧化菌（硝化菌科）和甲烷氧化菌（甲基球菌科）将CO和CH 4氧化为CO2，将NH 4+氧化为NO2-。然而，这两组生物体在各种环境中对CO、CH 4和NH 4+代谢的相对贡献尚不清楚。在氨氧化剂中，氨单加氧酶，负责将NH 4+转化为NH 2 OH的酶，也催化CH 4氧化为CH 3OH。氨单加氧酶也介导CH 3OH转化为CO2和细胞碳，但其途径尚不清楚。至少有一种氨氧化剂，海洋亚硝化球菌，表现出类似甲烷氧化菌的甲烷氧化Km。然而，氨氧化器中记录的甲烷氧化的最高速率仍然比甲烷氧化菌中的速率低五倍，并且氨氧化器显然不能在甲烷上生长。甲烷氧化菌通过甲烷单加氧酶将NH 4+氧化为NH 2 OH，通过甲烷单加氧酶将NH 4+氧化为NH 2 OH，通过NH 2 OH氧化酶将NH 2 OH氧化为NO2-，这可能类似于氨氧化剂中发现的酶。NH 4+氧化的最大速率显著低于氨氧化器，并且对NH 4+的亲和力通常低于氨氧化器。NH 4+显然不支持甲烷氧化菌的生长。氨单加氧酶和甲烷单加氧酶都将CO氧化为CO2，但CO不能支持氨氧化菌或甲烷氧化菌的生长。这些生物体对CO的亲和力与其生长底物的亲和力相当，并且通常高于一氧化碳细菌中的亲和力。甲烷氧化菌的甲烷单加氧酶以两种形式存在：可溶形式和颗粒形式。对可溶性形式进行了充分表征，并且似乎与颗粒物无关。氨单加氧酶和颗粒状甲烷单加氧酶有许多相似之处。两种酶都含有铜，并且是膜结合的。它们氧化各种无机和有机化合物，并且它们的抑制剂概况相似。被认为是特定的氨氧化剂的抑制剂已被用于硝化作用的环境研究。然而，几乎所有发现抑制氨氧化剂的化合物也抑制甲烷氧化菌，并且大多数抑制剂作用于单加氧酶。许多可能发挥其作用螯合铜，这是必不可少的一些单加氧酶的正常运作。缺乏对这两组细菌中的一组或另一组具有特异性的抑制剂阻碍了确定它们在自然界中的相对作用。
Ammonia oxidizers (family Nitrobacteraceae) and methanotrophs (family Methylococcaceae) oxidize CO and CH4 to CO2 and NH4+ to NO2-. However, the relative contributions of the two groups of organisms to the metabolism of CO, CH4, and NH4+ in various environments are not known. In the ammonia oxidizers, ammonia monooxygenase, the enzyme responsible for the conversion of NH4+ to NH2OH, also catalyzes the oxidation of CH4 to CH3OH. Ammonia monooxygenase also mediates the transformation of CH3OH to CO2 and cell carbon, but the pathway by which this is done is not known. At least one species of ammonia oxidizer, Nitrosococcus oceanus, exhibits a Km for CH4 oxidation similar to that of methanotrophs. However, the highest rate of CH4 oxidation recorded in an ammonia oxidizer is still five times lower than rates in methanotrophs, and ammonia oxidizers are apparently unable to grow on CH4. Methanotrophs oxidize NH4+ to NH2OH via methane monooxygenase and NH4+ to NH2OH via methane monooxygenase and NH2OH to NO2- via an NH2OH oxidase which may resemble the enzyme found in ammonia oxidizers. Maximum rates of NH4+ oxidation are considerably lower than in ammonia oxidizers, and the affinity for NH4+ is generally lower than in ammonia oxidizers. NH4+ does not apparently support growth in methanotrophs. Both ammonia monooxygenase and methane monooxygenase oxidize CO to CO2, but CO cannot support growth in either ammonia oxidizers or methanotrophs. These organisms have affinities for CO which are comparable to those for their growth substrates and often higher than those in carboxydobacteria. The methane monooxygenases of methanotrophs exist in two forms: a soluble form and a particulate form. The soluble form is well characterized and appears unrelated to the particulate. Ammonia monooxygenase and the particulate methane monooxygenase share a number of similarities. Both enzymes contain copper and are membrane bound. They oxidize a variety of inorganic and organic compounds, and their inhibitor profiles are similar. Inhibitors thought to be specific to ammonia oxidizers have been used in environmental studies of nitrification. However, almost all of the numerous compounds found to inhibit ammonia oxidizers also inhibit methanotrophs, and most of the inhibitors act upon the monooxygenases. Many probably exert their effect by chelating copper, which is essential to the proper functioning of some monooxygenases. The lack of inhibitors specific for one or the other of the two groups of bacteria hampers the determination of their relative roles in nature.