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In microbial nitrogen metabolism, the occurrence of hydrazine as an intermediate is rare. [36] Hydrazine has been proposed as an enzyme-bound intermediate in the nitrogenase reaction. [37] Recently, using detailed molecular analyses and combining complementary methods, Kartal and coworkers published strong evidence supporting the latter mechanism.
Dissimilatory nitrate reduction to ammonium is a two step process, reducing NO 3 − to NO 2 − then NO 2 − to NH 4 +, though the reaction may begin with NO 2 − directly. [1] Each step is mediated by a different enzyme, the first step of dissimilatory nitrate reduction to ammonium is usually mediated by a periplasmic nitrate reductase.
Glutamine synthetase (GS) (EC 6.3.1.2) [3] is an enzyme that plays an essential role in the metabolism of nitrogen by catalyzing the condensation of glutamate and ammonia to form glutamine: Glutamate + ATP + NH 3 → Glutamine + ADP + phosphate Glutamine synthetase catalyzed reaction
Isaac Asimov, the biochemist and science fiction writer, suggested in 1981 that poly-lipids could form a substitute for proteins in a non-polar solvent such as methane. [51] Lakes composed of a mixture of hydrocarbons, including methane and ethane , have been detected on the surface of Titan by the Cassini spacecraft .
Recent results, however, show that HAO does not produce nitrite as a direct product of catalysis. This enzyme instead produces nitric oxide and three electrons. Nitric oxide can then be oxidized by other enzymes (or oxygen) to nitrite. In this paradigm, the electron balance for overall metabolism needs to be reconsidered. [7]
Nitric oxide (nitrogen monoxide) is a molecule and chemical compound with chemical formula of N O. In mammals including humans, nitric oxide is a signaling molecule involved in several physiological and pathological processes. [1] It is a powerful vasodilator with a half-life of a few seconds in the blood.
The vocabulary includes words used in science fiction books, TV and film. A second category rises from discussion and criticism of science fiction, and a third category comes from the subculture of fandom. It describes itself as "the first historical dictionary devoted to science fiction", tracing how science fiction terms have developed over time.
Water is the medium of the oceans, the medium which carries all the substances and elements involved in the marine biogeochemical cycles. Water as found in nature almost always includes dissolved substances, so water has been described as the "universal solvent" for its ability to dissolve so many substances.