Ammonia
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Nitrogen Fixation
Looser non-symbiotic relationships (called associations) occur between diazotrophs and plants such as rice where nitrogen fixation takes place on the roots. The overall reaction for the conversion to ammonia enabled by the nitrogenase enzyme may be written: This can be seen to be an energy-intensive process by the requirement of 16 of the energy-rich ATP molecules. The conversion of N2 into ammonia occurs at a metal cluster called FeMoco, an abbreviation for the iron-molybdenum cofactor. The mechanism proceeds via a series of protonation and reduction steps wherein the FeMoco active site hydrogenates the N2 substrate. Some plants that contribute to nitrogen fixation are members of the legume family: kudzu, clover, soybean, alfalfa, lupin and peanut. They contain the symbiotic rhizobia bacteria within nodules in their root systems. These nodules limit exposure to oxygen, which rapidly decomposes the nitrogenase enzymes. Nitrogen fixation can occur in decomposing wood by diazotrophic bacterial communities. This can enrich the nitrogen content of the wood, enabling deadwood decomposition by fungi. A large amount of nitrogen fixation occurs in the oceans, perhaps half. The cyanobacteria in the seas are a major source of such production of nitrates. |
Index Reference Nitrogen fixation wiki Denton, Miracle of the Cell Chap 6 | ||
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