Publication Date:
1989-01-06
Description:
Elasmobranch fishes, the coelacanth, estivating lungfish, amphibians, and mammals synthesize urea by the ornithine-urea cycle; by comparison, urea synthetic activity is generally insignificant in teleostean fishes. It is reported here that isolated liver cells of two teleost toadfishes, Opsanus beta and Opsansus tau, synthesize urea by the ornithine-urea cycle at substantial rates. Because toadfish excrete ammonia, do not use urea as an osmolyte, and have substantial levels of urease in their digestive systems, urea may serve as a transient nitrogen store, forming the basis of a nitrogen conservation shuttle system between liver and gut as in ruminants and hibernators. Toadfish synthesize urea using enzymes and subcellular distributions similar to those of elasmobranchs: glutamine-dependent carbamoyl phosphate synthethase (CPS III) and mitochondrial arginase. In contrast, mammals have CPS I (ammonia-dependent) and cytosolic arginase. Data on CPS and arginases in other fishes, including lungfishes and the coelacanth, support the hypothesis that the ornithine-urea cycle, a monophyletic trait in the vertebrates, underwent two key changes before the evolution of the extant lungfishes: a switch from CPS III to CPS I and replacement of mitochondrial arginase by a cytosolic equivalent.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Mommsen, T P -- Walsh, P J -- New York, N.Y. -- Science. 1989 Jan 6;243(4887):72-5.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Division of Biology and Living Resources, Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, FL 33149.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/2563172" target="_blank"〉PubMed〈/a〉
Keywords:
Animals
;
Arginase/metabolism
;
*Biological Evolution
;
Carbamoyl-Phosphate Synthase (Ammonia)/metabolism
;
Carbamoyl-Phosphate Synthase (Glutamine-Hydrolyzing)/metabolism
;
Fishes/*metabolism
;
Glutamate-Ammonia Ligase/metabolism
;
Liver/metabolism
;
Species Specificity
;
Urea/*biosynthesis
;
Vertebrates/*metabolism
Print ISSN:
0036-8075
Electronic ISSN:
1095-9203
Topics:
Biology
,
Chemistry and Pharmacology
,
Computer Science
,
Medicine
,
Natural Sciences in General
,
Physics
Permalink
