| 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) |
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| 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) |
| nitrogen group | Five trivalent or quinquivalent elements whose hydrogen compounds are basic and whose oxyacids vary from monobasic to tetrabasic: nitrogen, phosphorus, arsenic, antimony, and bismuth. (05 Mar 2000) |
| nitrogen isotopes | Stable nitrogen atoms that have the same atomic number as the element nitrogen, but differ in atomic weight. N-15 is a stable nitrogen isotope. (12 Dec 1998) |
| nitrogen lag | The length of time after the ingestion of a given protein before the amount of nitrogen equal to that in the protein has been excreted in the urine. (05 Mar 2000) |
| nitrogen monoxide | <chemical> Nitrogen oxide (n2o). A colourless, odourless gas that is used as an anaesthetic and analgesic. High concentrations cause a narcotic effect and may replace oxygen, causing death by asphyxia. It is also used as a food aerosol in the preparation of whipping cream. Pharmacological action: aerosol propellants, analgesics, non-narcotic, anaesthetics, inhalation. Chemical name: Nitrogen oxide (N2O) (12 Dec 1998) |
| nitrogen mustard compounds | <chemical> A group of alkylating agents derived from mustard gas, with the sulfur replaced by nitrogen. They were formerly used as toxicants and vesicants, but now function as antineoplastic agent. These compounds are also powerful mutagens, teratogens, immunosuppressants, and carcinogens. Pharmacological action: antineoplastic agent, alkylating, carcinogens, mutagens, teratogens. (12 Dec 1998) |
| nitrogen mustards | <pharmacology> A series of tertiary amine compounds having vesicant properties similar to those of mustard gas. They have the general formula RN(CH2CH2Cl)2. They can alkylate compounds such as DNA and are used as the basis of cytostatic drugs for cancer chemotherapy. (18 Nov 1997) |
| nitrogen narcosis | Narcosis produced by nitrogenous materials such as occurs in certain forms of uraemia and hepatic coma, the stuporous condition characterised by disorientation and by loss of judgment and skill, attributed to an increased partial pressure of nitrogen in the inspired air of deepsea divers during underwater operations. Commonly referred to as "rapture of the deep." (05 Mar 2000) |
| nitrogen oxides | Inorganic oxides that contain nitrogen. (12 Dec 1998) |
| nitrogen partition | Determination of the distribution of nitrogen in the urine among the various constituents. Synonym: nitrogen distribution. (05 Mar 2000) |
| nitrogen radioisotopes | Unstable isotopes of nitrogen that decay or disintegrate emitting radiation. N atoms with atomic weights 12, 13, 16, 17, and 18 are radioactive nitrogen isotopes. (12 Dec 1998) |
| nonprotein 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) |
| undetermined nitrogen | The nitrogen of blood, urine, etc., other than urea, uric acid, amino acids, etc., that can be directly estimated; in blood it amounts to about 25 mg per 100 ml. Urea nitrogen, the portion of nitrogen in a biological sample, such as blood or urine, that derives from its content of urea. See: blood urea nitrogen. (05 Mar 2000) |
| urinary nitrogen | Nitrogen excreted as urea, amino acids, uric acid, etc., in the urine; 1 g of urinary nitrogen indicates the breakdown in the body of 6.25 g of protein. See: nitrogen equivalent. (05 Mar 2000) |