| Abstract from DBPedia | Nitrogen fixation is a chemical process by which molecular nitrogen (N2), with a strong triple covalent bond, in the air is converted into ammonia (NH3) or related nitrogenous compounds, typically in soil or aquatic systems but also in industry. Atmospheric nitrogen is molecular dinitrogen, a relatively nonreactive molecule that is metabolically useless to all but a few microorganisms. Biological nitrogen fixation or diazotrophy is an important microbials mediated process that converts dinitrogen (N2) gas to ammonia (NH3) using the nitrogenase protein complex (Nif). Nitrogen fixation is essential to life because fixed inorganic nitrogen compounds are required for the biosynthesis of all nitrogen-containing organic compounds, such as amino acids and proteins, nucleoside triphosphates and nucleic acids. As part of the nitrogen cycle, it is essential for agriculture and the manufacture of fertilizer. It is also, indirectly, relevant to the manufacture of all nitrogen chemical compounds, which includes some explosives, pharmaceuticals, and dyes. Nitrogen fixation is carried out naturally in soil by microorganisms termed diazotrophs that include bacteria, such as Azotobacter, and archaea. Some nitrogen-fixing bacteria have symbiotic relationships with plant groups, especially legumes. Looser non-symbiotic relationships between diazotrophs and plants are often referred to as associative, as seen in nitrogen fixation on rice roots. Nitrogen fixation occurs between some termites and fungi. It occurs naturally in the air by means of NOx production by lightning. All biological reactions involving the process of nitrogen fixation are catalyzed by enzymes called nitrogenases. These enzymes contain iron, often with a second metal, usually molybdenum but sometimes vanadium.窒素固定（ちっそこてい）とは、空気中に多量に存在する安定な（不活性）窒素分子を、反応性の高い他の窒素化合物（アンモニア、硝酸塩、二酸化窒素など）に変換するプロセスをいう。 自然界での窒素固定は、いくつかの真正細菌（細菌、放線菌、藍藻、ある種の嫌気性細菌など）と一部の古細菌（メタン菌など）によって行われる。これらの微生物には、種特異的に他の植物や、動物（シロアリなど）と共生関係を形成しているものもある。また、雷の放電や太陽からの紫外線、山火事や火力発電所、内燃機関での燃焼により、窒素ガスの酸化によって窒素酸化物が生成され、これらが雨水に溶けることで、土壌に固定される。 これとは逆に窒素化合物を分子状窒素として大気中へ放散させる作用または工程は脱窒と呼ばれ、窒素固定と合わさることで窒素循環が成立している。 また、アンモニア合成を代表として人工的に窒素分子を他の窒素化合物に変換する手法も幾つか開発されており、工業的に非常に重要な位置を占めている。 (Source: http://dbpedia.org/resource/Nitrogen_fixation) |
