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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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Journal ArticleDOI
TL;DR: In this paper, a mixture of SH-containing sulfur amino acids was heated with glucose in the presence and presence of the following potential inhibitors: N-acetyl-L-cysteine, L-cystine, reduced glutathione, sodium bisulfite, and urea.
Abstract: Amino acids interact with carbohydrates to form Maillard browning products. Such reactions reduce the nutritional value of foods containing amino acids and carbohydrates and may lead to the formation of compounds that are mutagenic and clastogenic or chromosome-damaging. A need therefore exists to inhibit these heat-induced interactions. To demonstrate whether SH-containing sulfur amino acids minimize nonenzymatic browning, beta-alanine, N alpha-acetyl-L-lysine, glycylglycine, and a mixture of amino acids were each heated with glucose in the absence and presence of the following potential inhibitors: N-acetyl-L-cysteine, L-cysteine, reduced glutathione, sodium bisulfite, and urea. Inhibition was measured as a function of temperature, time of heating, and concentration of reactants. The extent of browning was estimated by absorbance measurements at 420 nm. Inhibition was independent of the amino group containing reactant. The minimum concentrations for optimum inhibition, in moles of inhibitor per mole of D-glucose, were as follows: sodium bisulfite, 0.02; L-cysteine, 0.05; N-acetyl-L-cysteine, 0.2; reduced glutathione, 0.2; urea, 8. An "index of prevention" (IP) was used to calculate the inhibition at the optimum mole ratio range, where IP = 100 - [molar absorptivity value (MAV) of the amine compound + glucose + inhibitor] X 100/(MAV of the amine compound + glucose). The calculated values were about 90% in all cases. Possible mechanisms of browning prevention are discussed.

99 citations

Journal ArticleDOI
TL;DR: The results stress the necessity of Ni for urease activation and thus for the growth of plants on urea-based media.
Abstract: The effect of Ni supply on growth, N metabolism and leaf urease activity of six plant species (rye, wheat, soybean, rape, zucchini and sunflower) grown on urea-based nutrient solutions was investigated. Activity of urease, which is activated by Ni, was hardly detectable in plants of all six species grown without supplementary Ni. As a consequence Ni-deprived plants accumulated considerable amounts of urea, showed a reduced dry matter production and reduced total N concentrations. The lack of urease activation in low-Ni plants made them metabolically N deficient, which is illustrated by the chlorotic appearance of these plants. The soluble amino acid N concentration was reduced by inadequate Ni supply. The amide concentrations (glutamine, asparagine) were considerably affected in all species. The same applied to the concentrations of the urea cycle intermediates arginine, ornithine, and citrulline. These results stress the necessity of Ni for urease activation and thus for the growth of plants on urea-based media.

99 citations

Journal ArticleDOI
TL;DR: Urea has been used as a protein replacement for ruminants for almost a century as discussed by the authors, and it has been known that ruminant animals have the unique ability to convert nonprotein nitrogen (NPN) to protein.

99 citations

Journal ArticleDOI
TL;DR: Chemicals containing NH 2 in place of NOH, such as urea and urethan (= ethylcarbamate) do not inactivate or mutate transforming DNA at a significant rate, and formaldehyde and its oxidation products, formic acid, performic Acid, and di-hydroxymethyl peroxide do notInactivating DNA alterations.
Abstract: Agents containing a free-NOH group such as hydroxylamine, N-methylhydroxylamine, hydroxyurea, hydroxyurethan, and hydrazines produce H2O2 on exposure to oxygen. All these agents, H2O2 itself, and disuccinyl peroxide, predominantly induce inactivating DNA alterations, whereas their mutagenic effect (per lethal hit) on transformung DNA is small. Chemicals containing NH2 in place of NOH, such as urea and urethan (= ethylcarbamate) do not inactivate DNA. Formaldehyde and its oxidation products, formic acid, performic acid, and di-hydroxymethyl peroxide do not inactivate or mutate transforming DNA at a significant rate.

98 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20231,000
20221,982
2021433
2020502
2019589
2018557