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.

System and method for measuring blood urea nitrogen, blood osmolarity, plasma free hemoglobin and tissue water content

Abstract: Systems and methods are provided for noninvasively measuring the levels of urea, blood osmolarity (or Na + ), plasma free hemoglobin and tissue water content in a patient's blood or tissue. Light of selected wavelengths is passed through blood or body tissue and the transmitted or reflected light is detected and the detected signals can be electronically compared and manipulated to provide the non-invasive, continuous and quantitative display of a patient's blood urea, blood osmolarity (or Na + ), plasma free hemoglobin and tissue water content.

The gastric biology of Helicobacter pylori.

Abstract: ▪ Abstract Helicobacter pylori is a neutralophilic, gram-negative, ureolytic organism that is able to colonize the human stomach but does not survive in a defined medium with a pH <4.0 unless urea is present. In order to live in the gastric environment, it has developed a repertoire of acid resistance mechanisms that can be classified into time-independent, acute, and chronic responses. Time-independent acid resistance depends on the structure of the organism's inner and outer membrane proteins that have a high isoelectric point, thereby reducing their proton permeability. Acute acid resistance depends on the constitutive synthesis of a neutral pH optimum urease that is an oligomeric Ni2+-containing heterodimer of UreA and UreB subunits. Gastric juice urea is able to rapidly access intrabacterial urease when the periplasmic pH falls below ∼6.2 owing to pH-gating of a urea channel, UreI. This results in the formation of NH3, which then neutralizes the bacterial periplasm to provide a pH of ∼6.2 and an inne...

Aqueous urea solution destabilizes Aβ16–22 oligomers

Abstract: We use long multiple trajectories generated by molecular dynamics simulations to probe the stability of oligomers of Aβ16–22 (KLVFFAE) peptides in aqueous urea solution. High concentration of urea promotes the formation of β-strand structures in Aβ16–22 monomers, whereas in water they adopt largely compact random coil structures. The tripeptide system, which forms stable antiparallel β-sheet structure in water, is destabilized in urea solution. The enhancement of β-strand content in the monomers and the disruption of oligomeric structure occur largely by direct interaction of urea with the peptide backbone. Our simulations suggest that the oligomer unbinding dynamics is determined by two opposing effects, namely, by the increased propensity of monomers to form β-strands and the rapid disruption of the oligomers. The qualitative conclusions are affirmed by using two urea models. Because the proposed destabilization mechanism depends largely on hydrogen bond formation between urea and the peptide backbone, we predict that high urea concentration will destabilize oligomers of other amyloidogenic peptides as well.

Comparative biochemistry of urea synthesis. 3. Activities of urea-cycle enzymes in various higher and lower vertebrates.

Abstract: 4. The ratio of potassium to sodium decreased significantly with advancing age in kidney and heart tissue. 5. Nine tissues were analysed from a further five LK and five HK aged ewes. The skeletal muscle, liver, spleen and kidney (expressed on a fatand blood-free basis) of the aged HK ewes tended to have higher concentrations of potassium (1.5, 2*2, 3-6 and 1-9% respectively) and lower concentrations of sodium (10-7, 12 3, 9 2 and 4 8% respectively) than those of the aged LK ewes. 6. Rumen epithelium from LK sheep had a significantly lower potassium concentration (19.5%) than that from HK animals. 7. The fat content of the skeletal muscle of aged LK sheep was significantly higher (17 g. of fat/kg. wet wt. or about 48%) than that of aged HK'sheep but this difference was not found in a group of lambs of the same breed.

Maize Yield as Affected by Organic Inputs and Urea in the West African Moist Savanna

Abstract: Nutrient depletion is a major constraint to crop production for moist savanna soils, and inputs of nutrients are required to overcome this constraint. The impact of sole and combined applications of organic inputs (Ols) [fresh tree prunings, Pueraria phaseoloides (Roxb.) Benth. residues, and manure] and urea [(NH 2 ) 2 CO] on maize (Zea mays L.) performance was investigated at four sites in West Africa. Interactions between Ols and urea resulting in added benefits from their mixed rather than sole application were quantified, and likely causes were evaluated. Maize in the mixed treatments, receiving 45 kg ha -1 urea N and 45 kg ha -1 N as Ols, produced 1.6 and 3.7 Mg ha -1 grain in Sekou and Glidji, respectively. Based on the yields from sole application of either Ols or urea, added benefits from the mixture were 0.49 Mg ha -1 grain (P < 0.001) in Sekou and 0.58 Mg ha -1 (P < 0.15) in Glidji. These benefits were generated during grain filling, which was characterized by drought, and they were likely caused by improved soil water conditions with mixed applications compared with sole applications. Nitrogen recovery from urea was higher in the combined treatments (44% in Sekou and 32% in Glidji) relative to the sole urea treatments (22% in Sekou and 15% in Glidji). Positive interactions between Ols and urea occurred at two of four sites and were likely caused by improved soil water conditions after applying Ols. Organic inputs can alleviate constraints to crop growth other than N depletion and, as such, improve the use efficiency of N fertilizer.