Urea, a non-protein nitrogen for dairy cows, is rapidly hydrolyzed to ammonia by urease produced by ureolytic bacteria in the rumen, and the ammonia is used as nitrogen for rumen bacterial growth. However, there is limited knowledge with regard to the ureolytic bacteria community in the rumen. To explore the ruminal ureolytic bacterial community, urea, or acetohydroxamic acid (AHA, an inhibitor...

We perform molecular dynamics simulations of narrow single-walled carbon nanotubes (SWNTs) in aqueous urea to investigate the structure and dynamical behavior of urea molecules inside the SWNT. Even at low urea concentrations (e.g., 0.5 M), we have observed spontaneous and continuous filling of SWNT with a one-dimensional urea wire (leaving very few water molecules inside the SWNT). The urea wi...

Shangraw, Robert E., and Farook Jahoor. Effect of liver disease and transplantation on urea synthesis in humans: relationship to acid-base status. Am. J. Physiol. 276 (Gastrointest. Liver Physiol. 39): G1145–G1152, 1999.—It has been suggested that hepatic urea synthesis, which consumes HCO3 , plays an important role in acid-base homeostasis. This study measured urea synthesis rate (Ra urea) dir...

Urea in renal medullas is sufficiently high to perturb macromolecules, yet the cells survive and function. The counteracting osmolytes hypothesis holds that methylamines, such as glycine betaine (betaine) and glycerophosphocholine (GPC) in renal medullas, stabilize macromolecules and oppose the effects of urea. Although betaine counteracts effects of urea on macromolecules in vitro and protects...

Urea-induced protein denaturation is widely used to study protein folding and stability; however, the molecular mechanism and driving forces of this process are not yet fully understood. In particular, it is unclear whether either hydrophobic or polar interactions between urea molecules and residues at the protein surface drive denaturation. To address this question, here, many molecular dynami...

The absorption, translocation, and assimilation of urea, nitrate, and ammonium in tomato plants within 24 h after N labeled compounds were applied at four different growth stages: seedling, ̄owering, fruiting, and harvesting. The absorption of urea-N was only 25% of NO3-N at seedling stage, but it was up to about 80% of NO3-N at the subsequent growth stages. The translocation of urea-N was limit...

Urea is the major nitrogen form supplied as fertilizer in agricultural plant production but also an important nitrogen metabolite in plants. We report the cloning and functional characterization of AtDUR3, a high-affinity urea transporter in plants. AtDUR3 contains 14 putative transmembrane-spanning domains and represents an individual member in Arabidopsis that belongs to a superfamily of sodi...

Urea is the principal end-product of nitrogen metabolism in mammals and is excreted almost entirely through the kidney. Studies by Shannon (1, 2) in the dog and by Chasis and Smith (3, 4) in man have shown that the renal clearance of urea is less than the inulin or creatinine clearance at all rates of urine flow, and that the clearance of urea increases as the urine flow rises. These observatio...

To explain the large, opposite effects of urea and glycine betaine (GB) on stability of folded proteins and protein complexes, we quantify and interpret preferential interactions of urea with 45 model compounds displaying protein functional groups and compare with a previous analysis of GB. This information is needed to use urea as a probe of coupled folding in protein processes and to tune mol...

Urea in biological fluids has been determined by a variety of direct and indirect procedures. Some indirect methods depend on the hydrolysis of urea with the enzyme urease to form ammonia, with subsequent quantitation of the ammonia by nesslerization (1-4). Undesirable features of these indirect methods are the use of relatively unstable reagents and loss of ammonia during the procedure. Direct...