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  • 1
    Electronic Resource
    Electronic Resource
    Variation in urea excretion in the gulf toadfishOpsanus beta (1990)
    Springer
    Marine biology 106 (1990), S. 323-328 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Under long-term (24 h) control measurements, significant urea was excreted (15 to 90% of excreted nitrogen) byOpsanus beta (Goode and Bean) collected in 1989 from Biscayne Bay, Florida, USA. Urea excretion rates and plasma urea concentrations were not affected by antibiotic treatments which decreased intestinal microbe populations. These results suggest that nitrogen recycling by gut microbe urease is probably not significant in this species. Urea excretion rates increased significantly following 8 h of air-exposure and in response to high levels of NH4Cl. These results suggest that urea is synthesized and excreted by the toadfish primarily in situations that limit ammonia excretion. Thus, the ornithineurea cycle in the toadfish liver primarily maintains low concentrations of ammonia within the fish. High levels of variability in urea excretion rates and variation in response to air-exposure suggest that urea synthetic rates are affected by immediate past environmental conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01344308
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Hydrolytic enzymes in the two North Sea ctenophores Pleurobrachia pileus and Beroe gracilis (1984)
    Springer
    Marine biology 81 (1984), S. 123-130 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Hydrolytic enzyme activities were determined in tissue extracts of the two North Sea ctenophores Pleurobrachia pileus and Beroe gracilis. The following activities were measured in field samples and characterized according to their mean specific activities and their pH optima: protease, aminopeptidase, amylase, N-acetylglucosaminidase, β-glucosidase, chitinase, carboxylesterase, phosphatase. Many of the enzyme activities are correlated, indicating their control by the same factors (i.e. nutritional conditions). Differences found between the phosphatase activities and the apparent lack of the chitinolytic system in B. gracilis reflect the differences in body composition and food specialization in both ctenophores, respectively. The low amylase and β-glucosidase activities in both ctenophores agree with the low carbohydrate content of their prey. In spite of high carboxylesterase activities, no lipolytic activity was detected in either of the ctenophores. In a laboratory feeding experiment with P. pileus, the enzyme activities increased but did not reach the activities found in the field samples. In B. gracilis, seasonal variations of some enzyme activities are discussed in relation to the seasonal abundance of its prey, P. pileus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00393110
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Urea excretion as a strategy for survival in a fish living in a very alkaline environment (1989)
    [s.l.] : Nature Publishing Group
    Nature 337 (1989), S. 165-166 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Ammonia excretion by rainbow trout is impaired under alka-line conditions (/?H 〉 9.5) (refs 8,9). Trout are incapable of increasing urea production in the face of elevated ammonia levels, even via uricolysis3 and die when exposed to extremely alkaline conditions. The teleost, Oreochromis ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/337165a0
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Biochemical and environmental perspectives on nitrogen metabolism in fishes (1992)
    Springer
    Cellular and molecular life sciences 48 (1992), S. 583-593 
    Details
    ISSN: 1420-9071
    Keywords: Alanine ; ammonia ; argininolysis ; detoxification ; excretion ; glutamine ; ornithine-urea cycle ; teleost fish ; toxicity ; transport ; urea ; uricolysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Catabolism of nitrogen-containing substances makes a major contribution to the oxidative metabolism in teleostean fishes. In this review, we focus on aspects of the formation, transport, detoxification and excretion of the two most important nitrogenous products of fishes: ammonia (NH3 plus NH 4 + ) and urea. While NH 4 + makes up the bulk of nitrogenous waste, it is in equilibrium with the highly toxic NH3. Ammonia is generated in the liver and excreted through branchial, surface and renal routes. Innocuous urea is derived through hepatic uricolysis or argininolysis and voided through kidney, gill, skin or faeces. Under conditions hampering the release of ammonia, such as exposure to exogenous ammonia, water limitation, or alkaline conditions, some teleosts detoxify ammonia through synthesis of urea by the ornithine-urea cycle in liver. Ammonia and possibly alanine are the prevalent vehicles of internal nitrogen transport. Glutamine is immaterial to interorgan nitrogen transport in fishes, but plays a transient role in the detoxification of ammonia by brain glutamine synthetase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01920243
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    Paper (German National Licenses)
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