| carbon-nitrogen lyases | <enzyme> Enzymes that catalyze the cleavage of a carbon-nitrogen bond by means other than hydrolysis or oxidation. Subclasses are the ammonia-lyases, the amidine-lyases, the amine-lyases, and other carbon-nitrogen lyases. Registry number: EC 4.3 (12 Dec 1998) |
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| genes, nitrogen fixation | Regulatory and structural genes present in certain bacteria, algae and fungi that control the conversion of atmospheric nitrogen into biologically usable compounds; include nif structural genes (e.g., nifd, nifh) for nitrogenase and nitrate reductase as well as regulator genes nifa, nifb, ntra, ntrb, ntrc. Some are responsible for regulating transcription of genes involved in the assimilation of poor nitrogen sources in enteric bacteria. (12 Dec 1998) |
| rest nitrogen | The nitrogen content of other than protein bodies; e.g., about one-half the nonprotein nitrogen in the blood is contained in urea. Synonym: rest nitrogen. (05 Mar 2000) |
| heavy nitrogen | The less common stable nitrogen isotope, making up 0.37% of natural nitrogen. Synonym: heavy nitrogen. (05 Mar 2000) |
| nitrogen | <chemistry> A colourless nonmetallic element, tasteless and odorless, comprising four fifths of the atmosphere by volume. It is chemically very inert in the free state, and as such is incapable of supporting life (hence the name azote still used by French chemists); but it forms many important compounds, as ammonia, nitric acid, the cyanides, etc, and is a constituent of all organised living tissues, animal or vegetable. Symbol N. Atomic weight 14. It was formerly regarded as a permanent noncondensible gas, but was liquefied in 1877 by Cailletet of Paris, and Pictet of Geneva. Origin: L. Nitrum natron + -gen: cf. F. Nitrogene. See Niter. Source: Websters Dictionary (01 Mar 1998) |
| nitrogen-13 | A cyclotron-produced, positron-emitting radioisotope of nitrogen with a half-life of 9.97 minutes; used in protein metabolism studies and in positron-emission tomography. (05 Mar 2000) |
| nitrogen-14 | The common nitrogen isotope, making up 99.63% of natural nitrogen. (05 Mar 2000) |
| nitrogen-15 | The less common stable nitrogen isotope, making up 0.37% of natural nitrogen. Synonym: heavy nitrogen. (05 Mar 2000) |
| nitrogen balance | The difference between the total nitrogen intake by an organism and its total nitrogen loss. A normal, healthy adult has a zero nitrogen balance, Nin Nout (i.e., a positive nitrogen balance. (05 Mar 2000) |
| nitrogen compounds | Inorganic compounds that contain nitrogen as an integral part of the molecule. (12 Dec 1998) |
| nitrogen cycle | <biochemistry> The global cycle of moving various forms of nitrogen through the air, water, soil, plants, animals of the planet. See: nitrogen fixation. (09 Oct 1997) |
| nitrogen dioxide | <chemical> Nitrogen oxide (no2). A highly poisonous gas. Exposure produces inflammation of lungs that may only cause slight pain or pass unnoticed, but resulting oedema several days later may cause death. It is a major atmospheric pollutant that is able to absorb uv light that does not reach the earth's surface. Pharmacological action: oxidants, photochemical, poisons. Chemical name: Nitrogen oxide (NO2) (12 Dec 1998) |
| nitrogen distribution | Determination of the distribution of nitrogen in the urine among the various constituents. Synonym: nitrogen distribution. (05 Mar 2000) |
| nitrogen equivalent | The nitrogen content of protein; used in calculating the protein breakdown in the body from the nitrogen excreted in the urine, 1 g of nitrogen considered as having originated in 6.25 g of protein catabolised. (05 Mar 2000) |
| nitrogen fixation | <biochemistry> The incorporation of atmospheric nitrogen into ammonia by various bacteria, catalysed by nitrogenase. This is an essential stage in the nitrogen cycle and is the ultimate source of all nitrogen in living organisms. In the sea, the main nitrogen fixers are Cyanobacteria. There are several free living bacteria in soil that fix nitrogen including species of Azotobacter, Clostridium and Klebsiella. Rhizobium only fixes nitrogen when in symbiotic association, in root nodules, with leguminous plants. The oxygen sensitive nitrogenase is protected by plant produced leghaemoglobin and the plant obtains fixed nitrogen from the bacteria. See: Frankia. (18 Nov 1997) |