scispace - formally typeset
Search or ask a question
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.


Papers
More filters
Journal ArticleDOI
TL;DR: In this article, it was shown that changes in the diet lead to different levels of blood urea, which can be correlated with different rumen-ammonia concentrations; the change in blood-urea concentration follows increases or decreases in rumen ammonia after a delay period of 4-8 hours.
Abstract: 1. It has been shown that under a given feeding regime the concentration of blood urea in the sheep is constant.2. Changes in the diet lead to different levels of blood-urea concentration which can be correlated with different rumen-ammonia concentrations; the change in blood-urea concentration follows increases or decreases in rumen ammonia after a delay period of 4–8 hr.3. Fluctuations in blood-urea concentration in the sheep are not primarily due to changes in the overall nitrogen intake.4. It is suggested that these findings might form the basis of a supplementary test in assessing the value of the protein in a foodstuff for ruminants.

193 citations

Journal ArticleDOI
TL;DR: Only by considering Ce as the true end-HD urea concentration it is possible to minimize the errors arising from the application of a single pool analysis to a two pool system.

192 citations

Journal ArticleDOI
01 May 1998-Proteins
TL;DR: The data support a model in which urea denatures proteins by decreasing the hydrophobic effect and by directly binding to the amide units via hydrogen bonds, and indicate that the enthalpy of amide hydrogen bond formation in water is considerably higher than previously estimated.
Abstract: The effects of urea on protein stability have been studied using a model system in which we have determined the energetics of dissolution of a homologous series of cyclic dipeptides into aqueous urea solutions of varying concentration at 25 degrees C using calorimetry. The data support a model in which urea denatures proteins by decreasing the hydrophobic effect and by directly binding to the amide units via hydrogen bonds. The data indicate also that the enthalpy of amide hydrogen bond formation in water is considerably higher than previously estimated. Previous estimates included the contribution of hydrophobic transfer of the alpha-carbon resulting in an overestimate of the binding between urea and the amide unit of the backbone and an underestimate of the binding enthalpy.

192 citations

Journal ArticleDOI
TL;DR: expression studies in Xenopus oocytes demonstrated that HUT11 mediates a facilitated urea transport that was inhibited, as described in mammalian erythrocytes, by very low concentrations of phloretin, p-chloromercuribenzene sulfonate, and urea analogues.

191 citations

Journal ArticleDOI
TL;DR: A mechanism of action for urease is proposed which involves initially an O-bonded complex between urea and an active-site Ni2+ ion and subsequently anO-bonding carbamato-enzyme intermediate.
Abstract: Acetamide and N-methylurea have been shown for the first time to be substrates for jack bean urease. In the enzymatic hydrolysis of urea, formamide, acetamide, and N-methylurea at pH 7.0 and 38 degrees C, kcat has the values 5870, 85, 0.55, and 0.075 s-1, respectively. The urease-catalyzed hydrolysis of all these substrates involves the active-site nickel ion(s). Enzymatic hydrolysis of the following compounds could not be detected: phenyl formate, p-nitroformanilide, trifluoroacetamide, p-nitrophenyl carbamate, thiourea, and O-methylisouronium ion. In the enzymatic hydrolysis of urea, the pH dependence of kcat between pH 3.4 and 7.8 indicates that at least two prototropic forms are active. Enzymatic hydrolysis of urea in the presence of methanol gave no detectable methyl carbamate. A mechanism of action for urease is proposed which involves initially an O-bonded complex between urea and an active-site Ni2+ ion and subsequently an O-bonded carbamato-enzyme intermediate.

190 citations


Network Information
Related Topics (5)
Amino acid
124.9K papers, 4M citations
86% related
Calcium
78.5K papers, 2.2M citations
85% related
Fatty acid
74.5K papers, 2.2M citations
82% related
Ascorbic acid
93.5K papers, 2.5M citations
80% related
Glutathione
42.5K papers, 1.8M citations
78% related
Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20231,000
20221,982
2021433
2020502
2019589
2018557