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.

Dogmas and controversies in the handling of nitrogenous wastes: the effect of feeding and fasting on the excretion of ammonia, urea and other nitrogenous waste products in rainbow trout.

Abstract: SUMMARY Ammonia and urea are the primary forms of nitrogen excretion in teleost fish. There exists, however, a discrepancy between the sum of ammonia plus urea nitrogen and total nitrogen, indicating that `unknown9 nitrogen end products may play an important role in nitrogen metabolism. The current study analysed a wide range of nitrogen end products in both fed and fasted juvenile rainbow trout. Ammonia-N (53–68%) and urea-N (6–10%) were confirmed as the most important forms of nitrogenous waste, but an interesting finding was the considerable excretion of nitrogen as amino acids (4–10%), via the gills, and as protein (3–11%), probably via the body mucus. Use of anal sutures delineated an important role for the gastrointestinal tract in the production of ammonia-N and urea-N in fed fish, but amino acid-N and protein-N output by this route were both negligible. Alternative nitrogen products – trimethylamine, trimethylamine oxide, uric acid, and nitrite + nitrate – were not excreted in detectable quantities. Creatine-N and creatinine-N outputs were detected but contributed only a small fraction to total nitrogen excretion (<1.4%). Despite the wide scope of nitrogenous end products investigated, a considerable proportion (12–20%) of nitrogen excretion remains unknown. Possible alternative end products and methodological considerations are proposed to explain this phenomenon. The findings described above were used to recalculate the nitrogen quotient (NQ=ṀN/ṀO2) on trout that had been either fasted or fed various daily rations (1%, 3% or 5% dry food per unit wet body mass per day). Feeding increased oxygen consumption (ṀO2) and total-N excretion (ṀN). The NQ is often used as a measure of protein utilisation in aerobic metabolism and assumes that all protein (and amino acid) fuels are converted by oxidation to nitrogenous waste products that are excreted. However, the results showed that calculation of the NQ based on total nitrogen excretion may overestimate protein utilisation in aerobic metabolism because of significant excretion of N in the form of proteins and amino acids, whereas the use of summed ammonia-N and urea-N excretion probably underestimates the contribution of protein towards aerobic metabolism. These errors increase as ration increases, because the discrepancy between total-N excretion and ammonia-N + urea-N excretion increases.

Utilization of Urea by Some Marine PHYTOPLANKTERS1

Abstract: Three diatoms from the Sargasso Sea and two diatoms and a haptophyte flagellate from an inshore area near Woods IIolc exhibited similar growth rates on urea, nitrate, and ammonia. A coccolithophore Emiliana (Coccolithus) huxleyi from the Sargasso Sea did not grow on urea. The half-saturation constant (K) for urea determined for one inshore diatom, Stephanopyxis costata ( Skeletonema costatum), was 8.5 pg-atom urea-N liter-l. At the urea concentrations of its habitats, the calculated division rate for this species, growing on urea as the sole nitrogen source, was 2.2 days, similar to that of diatoms growing in inshore habitats. It appears, from data on natural urea concentrations and urea uptake rates by S. costata, that urea can be ,a significant N source for at least one common inshore phytoplankter. According to growth rate studies, at least three inshore and three offshore marine phytoplankton can grow as rapidly on urea as on nitrate or ammonia,

Ethyl Carbamate Formation in Wine: Use of Radioactively Labeled Precursors to Demonstrate the Involvement of Urea

Abstract: The formation of ethyl carbamate was investigated in model solutions and in wines using radioactively labeled urea and monitoring the appearance of that radioactivity in ethyl carbamate. There was a striking temperature dependence for the rate of the reaction as well as a dependence upon urea and ethanol concentrations. The source of urea during fermentation was investigated using radioactively labeled arginine ( guanido - 14 C). Under the conditions used here, arginine was degraded to urea, and some urea was released into the fermentation medium. More urea could be released from the cells when ethanol concentration was elevated, as a consequnce of fortification of the must. There was significant turnover and degradation of arginine in cells incubated in the presence of ethanol, as would occur during commercial fortification of musts. Thus, urea can be formed during vinification and, if released into the medium, will yield ethyl carbamate through reaction with ethanol.