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Hepatic and extrahepatic distribution of ornithine urea cycle enzymes in holocephalan elephant fish (Callorhinchus milii)


Takagi, W and Kajimura, M and Bell, JD and Toop, T and Donald, JA and Hyodo, S, Hepatic and extrahepatic distribution of ornithine urea cycle enzymes in holocephalan elephant fish (Callorhinchus milii), Comparative Biochemistry and Physiology - B Biochemistry and Molecular Biology, 161, (4) pp. 331-340. ISSN 1096-4959 (2012) [Refereed Article]

DOI: doi:10.1016/j.cbpb.2011.12.006


Cartilaginous fish comprise two subclasses, the Holocephali (chimaeras) and Elasmobranchii (sharks, skates and rays). Little is known about osmoregulatory mechanisms in holocephalan fishes except that they conduct urea-based osmoregulation, as in elasmobranchs. In the present study, we examined the ornithine urea cycle (OUC) enzymes that play a role in urea biosynthesis in the holocephalan elephant fish, Callorhinchus milii (cm). We obtained a single mRNA encoding carbamoyl phosphate synthetase III (cmCPSIII) and ornithine transcarbamylase (cmOTC), and two mRNAs encoding glutamine synthetases (cmGSs) and two arginases (cmARGs), respectively. The two cmGSs were structurally and functionally separated into two types: brain/liver/kidney-type cmGS1 and muscle-type cmGS2. Furthermore, two alternatively spliced transcripts with different sizes were found for cm. gs1 gene. The longer transcript has a putative mitochondrial targeting signal (MTS) and was predominantly expressed in the liver and kidney. MTS was not found in the short form of cmGS1 and cmGS2. A high mRNA expression and enzyme activities were found in the liver and muscle. Furthermore, in various tissues examined, mRNA levels of all the enzymes except cmCPSIII were significantly increased after hatching. The data show that the liver is the important organ for urea biosynthesis in elephant fish, but, extrahepatic tissues such as the kidney and muscle may also contribute to the urea production. In addition to the role of the extrahepatic tissues and nitrogen metabolism, the molecular and functional characteristics of multiple isoforms of GSs and ARGs are discussed. © 2011 Elsevier Inc.

Item Details

Item Type:Refereed Article
Keywords:Cartilaginous fish; Elephant fish; Extrahepatic tissues; Ornithine urea cycle enzymes; Urea synthesis; arginase; carbamoyl phosphate synthase; enzyme; glutamate ammonia ligase; messenger RNA; ornithine; ornithine carbamoyltransferase; urea; article
Research Division:Agricultural, Veterinary and Food Sciences
Research Group:Fisheries sciences
Research Field:Fish physiology and genetics
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the biological sciences
UTAS Author:Bell, JD (Dr Justin Bell)
ID Code:82460
Year Published:2012
Web of Science® Times Cited:13
Deposited By:Sustainable Marine Research Collaboration
Deposited On:2013-02-04
Last Modified:2013-06-06

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