Topic
Urea
About: Urea is a research topic. Over the lifetime, 21394 publications have been published within this topic receiving 382444 citations. The topic is also known as: carbamide & carbonic acid diamide.
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TL;DR: Teleostean fish species of the family Batrachoididae (toadfishes and midshipmen) possess high titers of all enzymes of the ornithine-urea cycle in their livers, and one species in particular, the gulf toadfish, has been shown to rapidly switch from ammonia excretion to urea synthesis and excretion during a variety of stress conditions.
Abstract: Selected teleostean (bony) fish species of the family Batrachoididae (toadfishes and midshipmen) possess high titers of all enzymes of the ornithine-urea cycle in their livers. These species have proven valuable in understanding the short-term regulation of urea synthesis, urea permeability, and transport across epithelial tissues, and how urea synthesis and excretion have evolved among vertebrates. One species in particular, the gulf toadfish (Opsanus beta), has been shown to rapidly switch from ammonia excretion to urea synthesis and excretion during a variety of stress conditions (including confinement). The transition is accompanied by an upregulation of hepatic glutamine synthetase activity, and a switch to pulsatile urea excretion from the anterior end of the fish. In fact, a single day's excretion can be voided in a period of < 3 h. Hypotheses on the environmental significance of these patterns of urea synthesis and excretion are discussed.
81 citations
TL;DR: The M4-lactate dehydrogenase of the freshwater elasmobranch,Potamotrygon sp.
Abstract: The kinetic properties — apparentKm of pyruvate, pyruvate inhibition pattern, and maximal velocity — of M4 (skeletal muscle) lactate dehydrogenases of marine elasmobranch fishes resemble those of the homologous lactate dehydrogenases of non-elasmobranchs only when physiological concentrations of urea (approximately 400 mM) are present in the assay medium. Urea increases the apparentKm of pyruvate to values typical of other vertebrates (Fig. 2), and reduces pyruvate inhibition to levels seen with other M4-lactate dehydrogenases (Fig. 3). Urea reduces the activation enthalpy of the reaction, and increasesVmax at physiological temperatures (Fig. 4).
81 citations
01 Jan 1955
TL;DR: This investigator added urea which had been labeled with N16 to a diet containing casein, and observed the extent of excretion and the degree of incorporation of the isotope in certain tissue constituents led him to conclude that urea is devoid of any metabolic activity.
81 citations
TL;DR: In this paper, a method for the incorporation of urease into a polypyrrole film by galvanostatic polymerisation on gold-coated plastic films and solid gold electrodes was described.
81 citations
TL;DR: In this paper, two field experiments were conducted during three consecutive years to evaluate influence of urea and ammonium sulfate application on grain yield, soil pH, calcium (Ca), magnesium (Mg) saturation, base saturation, aluminum (Al), and acidity (H + Al) saturation in lowland rice production.
Abstract: Urea and ammonium sulfate are principal nitrogen (N) sources for crop production. Two field experiments were conducted during three consecutive years to evaluate influence of urea and ammonium sulfate application on grain yield, soil pH, calcium (Ca) saturation, magnesium (Mg) saturation, base saturation, aluminum (Al) saturation, and acidity (H + Al) saturation in lowland rice production. Grain yield was significantly influenced by urea as well as ammonium sulfate fertilization. Soil pH linearly decreased with the application of N by ammonium sulfate and urea fertilizers. However, the magnitude of the pH decrease was greater by ammonium sulfate than by urea. The Ca and Mg saturations were decreased at the greater N rates compared to low rates of N by both the fertilizer sources. The Al and acidity saturation increased with increasing N rates by both the fertilizer sources. However, these acidity indices were increased more with the application of ammonium sulfate compared with urea. Rice grain yield had negative associations with pH, Ca saturation, Mg saturation, and base saturation and positive associations with Al and acidity saturation. This indicates that rice plant is tolerant to soil acidity.
81 citations