| Urea formation in rat, bovine, and human lens. | |
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MedLine Citation:
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PMID: 6662205 Owner: NLM Status: MEDLINE |
Abstract/OtherAbstract:
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Lenses produce both ammonia and urea, and a previous report suggested that bovine lenses contain a complete urea cycle capable of synthesizing urea from bicarbonate and ammonia. To determine whether lenses produce urea by a complete urea cycle or by arginase alone, intact lenses were cultured with [guanido-14C]-arginine or [14C]-bicarbonate. The [14C]-urea was volatilized to [14C]-CO2 by urease and collected in KOH. The cultured rat, bovine and human lenses produced [14C]-urea from [14C]-arginine; therefore lens arginase activity was also examined in homogenates of rat and human lenses. Rat lens homogenates had constant arginase activity for at least 2 hr at 37 degrees C, and activity increased linearly with the concentration of lens homogenate. Rat lens arginase had an apparent Vmax of approximately 13 nmol/hr/mg lens wet weight in lens homogenates and produced 4-6 nmol urea/hr/mg at 25 mM arginine. Human lens homogenates produced 1-5 nmol/hr/mg. In contrast, neither bovine nor rat lenses cultured with [14C]-bicarbonate produced detectable [14C]-urea, although label was incorporated into unidentified nonvolatile products. These products were shown by ion exchange chromatography and enzymatic assay to contain no detectable arginine or urea. It was concluded that although arginase activity is present, neither rat nor bovine lenses contain significant urea cycle activity. However, it is possible that arginase serves as a source of lens ornithine. |
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Authors:
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H M Jernigan |
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Publication Detail:
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Type: In Vitro; Journal Article; Research Support, U.S. Gov't, P.H.S. |
Journal Detail:
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Title: Experimental eye research Volume: 37 ISSN: 0014-4835 ISO Abbreviation: Exp. Eye Res. Publication Date: 1983 Dec |
Date Detail:
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Created Date: 1984-03-23 Completed Date: 1984-03-23 Revised Date: 2007-11-14 |
Medline Journal Info:
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Nlm Unique ID: 0370707 Medline TA: Exp Eye Res Country: ENGLAND |
Other Details:
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Languages: eng Pagination: 551-8 Citation Subset: IM |
Export Citation:
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APA/MLA Format Download EndNote Download BibTex |
| MeSH Terms | |
Descriptor/Qualifier:
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Adult Aged Animals Arginase / metabolism Arginine / metabolism Bicarbonates / metabolism Carbon Radioisotopes / diagnostic use Cattle Cells, Cultured Humans Lens, Crystalline / enzymology, metabolism* Middle Aged Rats Urea / biosynthesis* |
| Grant Support | |
ID/Acronym/Agency:
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EY 02665/EY/NEI NIH HHS |
| Chemical | |
Reg. No./Substance:
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0/Bicarbonates; 0/Carbon Radioisotopes; 57-13-6/Urea; 74-79-3/Arginine; EC 3.5.3.1/Arginase |
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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