Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.5.1.5 (urease)
 7,257 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Hydrolysis of arginine into urea and ornithine (Orn) was observed to take place in several segments of the rat nephron including cortical and medullary pars recta of the proximal tubule (PST) and collecting duct (CD). This work was now extended to the adult mouse and rabbit. Representative nephron segments, obtained by microdissection of collagenase-treated kidneys, were incubated with L-[guanido-14C]arginine (216 microM). Addition of urease produced 14CO2 + 2 NH3 from the newly formed urea released in the incubate. 14CO2 was trapped in KOH and counted. In both species, as well as in the rat, the PST was the site of the highest urea + Orn production, with an intensity increasing from cortex to medulla. For other nephron segments, the pattern was not similar in all species. Significant production of urea + Orn was observed in the proximal convoluted tubule and the medullary thick ascending limb in the rabbit, but not in the CD of either the rabbit or the mouse. The functional significance of this urea + Orn production remains unclear. The total amount of urea generated intrarenally by this reaction does not seem sufficient to play a significant role in the urinary concentrating mechanism. It may be assumed that Orn could be further metabolized to polyamines and play a role in maintaining cell integrity and function in the PST, especially in its medullary part, exposed to hypertonicity and poor oxygen supply.
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PMID:Localization of urea and ornithine production along mouse and rabbit nephrons: functional significance. 144 76

Arginine production was measured in isolated rat nephron segments. Segments were incubated with 0.3 mM aspartate and 0.1 mM L-[ureido-14C]-citrulline in a sealed chamber. Arginase and urease were added to the medium to hydrolyze arginine and to release 14CO2, which was trapped in KOH and counted. Arginine synthesis was found only in the proximal tubule, with decreasing intensity from proximal convoluted (PCT) to proximal straight tubule (PST). Results were as follows (in fmol.min-1.mm tubule length-1): PCT, 122 +/- 15; cortical PST, 71 +/- 6; outer medullary PST, 41 +/- 4; all other segments, less than 6. Arginine synthesis changed almost proportionally with precursor concentration of less than or equal to 0.4 mM. We had shown previously that PST but not PCT was able to hydrolyze arginine into urea and ornithine. In this study arginine was further hydrolyzed in cortical (40%) and medullary (64%) PST but not in PCT. These observations suggest that the arginine formed in PCT contributes to the maintenance of the whole body arginine pool, whereas most of the arginine formed in PST might contribute, by its conversion to urea, to the process of urine concentration.
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PMID:Localization of arginine synthesis along rat nephron. 226 Jun 85

Accelerated rates of ammonia production by the renal proximal tubule constitute an important adaptation to chronic renal injury. Although serving to maintain net acid excretion, this augmented production of ammonia per nephron results in increased renal cortical levels of ammonia and contributes to progressive renal injury. Ammonia fosters progressive injury via its ability to modify the third component of complement and initiate alternative complement pathway activity. This interaction of ammonia with complement incites inflammation in models of nonimmune chronic renal disease in the rat and may contribute to tissue injury in pyelonephritis involving urease-positive organisms. The long recognized in vivo association between increased renal ammoniagenesis, renal growth, and progressive injury in several models of renal disease has been advanced by the recent demonstration of ammonia as a direct stimulus to growth of renal tubular epithelium in culture. Additionally, evidence from studies of acute ischemic renal injury suggests a contributory role for ammonia in mediating tissue injury in this model. Elevated renal levels of ammonia, therefore, contribute to tubulointerstitial injury primarily through the proinflammatory and growth-promoting properties of ammonia.
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PMID:Role of ammonia in tubulointerstitial injury. 228 94

In the rat kidney, arginine (Arg) synthesis is restricted to the proximal tubule with a decreasing intensity from its convoluted (PCT) to its straight part (PST). The present study was designed to investigate the pattern of Arg synthesis along the nephron in other mammals, the mouse and rabbit. Microdissected representative nephron segments were incubated with 0.1 mM L-[ureido-14C]citrulline in a sealed chamber. Addition of arginase and urease to the incubation medium led to the hydrolysis of Arg into ornithine, NH3, and 14CO2. The latter was trapped in KOH and counted (results are in fmol Arg.min-1.mm tubular length-1). As in the rat, the main site of Arg synthesis in both species was found to be the PCT (mouse, 191; and rabbit, 57). A lower production was observed in rabbit and mouse PST and in rabbit distal segments. Along the PCT (from 1st to 4th mm after the glomerulus), a steep decrease is observed in mouse (595 and 37, respectively) but not in rabbit (57 and 23). The fate of the newly synthesized Arg probably depends on its site of production. Intracellular arginase activity is known to be present in the cortical (C) and medullary (OS) PST, in both mouse and rabbit. In rabbit only, arginase activity is also found in the PCT. We observed that a large part of Arg was further hydrolyzed into urea and ornithine in CPST and OSPST of mouse (66 and 80%, respectively) and rabbit (40 and 70%) but not in rabbit PCT (8%). Thus Arg produced by PCT in both species is probably released in the cortical blood, whereas Arg produced in PST may serve locally to produce urea and ornithine, and the latter could be used for polyamine synthesis.
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PMID:Arginine synthesis in mouse and rabbit nephron: localization and functional significance. 832 90