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: A group of Xenopus laevis were found which had been naturally aestivating in the mud near a dried-up pool, and on return to water, these animals did not gain weight, but excreted large amounts of urea.
94 citations
TL;DR: The rate of hydrolysis of urea in soil over a wide range of concentrations, up to 10 moles N per dm3 soil solution, found in fertilizer practice, was examined in Begbroke sandy loam adjusted to different pH values as discussed by the authors.
Abstract: SUMMARY
The rate of hydrolysis of urea in soil over the wide range of concentrations, up to 10 moles N per dm3 soil solution, found in fertilizer practice, was examined in Begbroke sandy loam adjusted to different pH values.
On rewetting air-dry soil, urease activity increased rapidly, reached a maximum within the first 24 h and then decreased slowly to level off after about 4 days. Pretreatment of the soil with urea or ammonium had no effect on the urease activity.
Urease activity increased with substrate concentration, reached an optimum value and then decreased with rising urea concentration. The results could be explained by substrate inhibition at higher urea concentrations, and the data are well described by a modified Michaelis-Menten equation involving three parameters, Vmax, Km and Ki where Ki is an inhibition constant. Km decreased linearily with rise in pH whereas Ki increased slightly between pH 4.9 and 7.0 and steeply between 7.0 and 8.4. Vmax increased with rise in pH, reached a maximum value at pH 6.0 and then declined at higher pHs.
There was a further reaction, reaching a maximum rate at a urea concentration of about 0.2 molar N in the soil solution, that followed Michaelis-Menten kinetics. Km for this high affinity reaction increased up to pH 7.2 and then decreased at higher pH values; Vmax increased up to pH 6.8 and then decreased. The contribution of the high affinity reaction was small except at low concentrations of urea.
94 citations
TL;DR: Li et al. as mentioned in this paper investigated the effects of urea-N application rates and Limus® (a new urease inhibitor consisting of 75% N-(n-butyl) thiophosphoric triamide (NBPT) and 25% N(n-propyl) THIophosphric triamide(NPPT)) in winter wheat.
94 citations
TL;DR: It is demonstrated that a scenario based on the formation of a urea/ammonium formate/water (UAFW) eutectic solution leads to an increase in phosphorylation when compared to urea alone for phosphate sources of varying solubility, suggesting that the prebiotic concentrations of urea in a geologically plausible evaporitic environment could solve the problem of organic phosphorylated on a prebiotics Earth.
Abstract: The poor reactivity of insoluble phosphates, such as apatite-group minerals, has been a long-appreciated obstacle for proposed models of prebiotic organophosphate formation. This obstacle presents a significant challenge to the nascent development of an RNA world and other models for the origins of life on Earth. Herein, we demonstrate that a scenario based on the formation of a urea/ammonium formate/water (UAFW) eutectic solution leads to an increase in phosphorylation when compared to urea alone for phosphate sources of varying solubility. In addition, under evaporative conditions and in the presence of MgSO4 , the UAFW eutectic mobilizes the phosphate sequestered in water-insoluble hydroxyapatite, giving rise to a marked increase in phosphorylation. These results suggest that the prebiotic concentrations of urea in a geologically plausible evaporitic environment could solve the problem of organic phosphorylation on a prebiotic Earth.
94 citations
TL;DR: Results indicate that UT3 functions as a urea/water channel utilizing a common aqueous pathway and the water transporting function and low urea reflection coefficient of UT3 in vasa recta may be important for the formation of a concentrated urine by countercurrent exchange in the kidney.
94 citations