scholarly journals Urea synthesis in the African lungfish Protopterus dolloi - hepatic carbamoyl phosphate synthetase III and glutamine synthetase are upregulated by 6 days of aerial exposure

2003 ◽  
Vol 206 (20) ◽  
pp. 3615-3624 ◽  
Author(s):  
S. F. Chew
Keyword(s):  
Glutamine Synthetase ◽  
Urea Synthesis ◽  
Carbamoyl Phosphate Synthetase ◽  
Aerial Exposure ◽  
Carbamoyl Phosphate ◽  
African Lungfish ◽  
Protopterus Dolloi

scholarly journals Glutamine-dependent carbamoyl-phosphate synthetase and other enzyme activities related to the pyrimidine pathway in spleen of Squalus acanthias (spiny dogfish)

1989 ◽  
Vol 261 (2) ◽  
pp. 523-529 ◽  
Author(s):  
P M Anderson
Keyword(s):  
Glutamine Synthetase ◽  
Enzyme Activities ◽  
Squalus Acanthias ◽  
Spiny Dogfish ◽  
Urea Synthesis ◽  
Carbamoyl Phosphate Synthetase ◽  
Carbamoyl Phosphate ◽  
Pyrimidine Nucleotide ◽  
Aspartate Carbamoyltransferase ◽  
Pyrimidine Pathway

The first two steps of urea synthesis in liver of marine elasmobranchs involve formation of glutamine from ammonia and of carbamoyl phosphate from glutamine, catalysed by glutamine synthetase and carbamoyl-phosphate synthetase, respectively [Anderson & Casey (1984) J. Biol. Chem. 259, 456-462]; both of these enzymes are localized exclusively in the mitochondrial matrix. The objective of this study was to establish the enzymology of carbamoyl phosphate formation and utilization for pyrimidine nucleotide biosynthesis in Squalus acanthias (spiny dogfish), a representative elasmobranch. Aspartate carbamoyltransferase could not be detected in liver of dogfish. Spleen extracts, however, had glutamine-dependent carbamoyl-phosphate synthetase, aspartate carbamoyltransferase, dihydro-orotase, and glutamine synthetase activities, all localized in the cytosol; dihydro-orotate dehydrogenase, orotate phosphoribosyltransferase, and orotidine-5′-decarboxylase activities were also present. Except for glutamine synthetase, the levels of all activities were very low. The carbamoyl-phosphate synthetase activity is inhibited by UTP and is activated by 5-phosphoribosyl 1-pyrophosphate. The first three enzyme activities of the pyrimidine pathway were eluted in distinctly different positions during gel filtration chromatography under a number of different conditions; although complete proteolysis of inter-domain regions of a multifunctional complex during extraction cannot be excluded, the evidence suggests that in dogfish, in contrast to mammalian species, these three enzymes of the pyrimidine pathway exist as individual polypeptide chains. These results: (1) establish that dogfish express two different glutamine-dependent carbamoyl-phosphate synthetase activities, (2) confirm the report [Smith, Ritter & Campbell (1987) J. Biol. Chem. 262, 198-202] that dogfish express two different glutamine synthetases, and (3) provide indirect evidence that glutamine may not be available in liver for biosynthetic reactions other than urea formation.

Subcellular localization and biochemical properties of the enzymes of carbamoyl phosphate and urea synthesis in the batrachoidid fishes Opsanus beta, Opsanus tau and Porichthys notatus

1995 ◽  
Vol 198 (3) ◽  
pp. 755-766 ◽  
Author(s):  
P Walsh
Keyword(s):  
Glutamine Synthetase ◽  
Subcellular Localization ◽  
Biochemical Properties ◽  
Nitrogen Excretion ◽  
Urea Synthesis ◽  
Carbamoyl Phosphate ◽  
Opsanus Beta ◽  
Opsanus Tau ◽  
Porichthys Notatus ◽  
The Family

The subcellular localization and biochemical properties of the enzymes of carbamoyl phosphate and urea synthesis were examined in three representatives of fishes of the family Batrachoididae, the gulf toadfish (Opsanus beta), the oyster toadfish (Opsanus tau) and the plainfin midshipman (Porichthys notatus). The primary objective of the study was to compare the biochemical characteristics of these fishes, which represent a range between ammoniotelism and ureotelism (O. beta being facultatively ureotelic), with previous patterns observed for an ammoniotelic teleost (Micropterus salmoides, the largemouth bass) and an obligate ureogenic elasmobranch (Squalus acanthias, the dogfish shark). The present study documents the expression of mitochondrial carbamoyl phosphate synthetase (CPSase) III and cytosolic CPSase II (and its associated enzymes of pyrimidine synthesis, dihydro-orotase and aspartate carbamoyltransferase) in the livers of all three batrachoidid species. Both mitochondrial and cytosolic activities of arginase were present in the livers of all three species, as were cytosolic glutamine synthetase and argininosuccinate synthetase and lyase. However, O. beta also showed mitochondrial glutamine synthetase activity and higher total hepatic levels of glutamine synthetase than either O. tau or P. notatus. Taken together, these observations confirm that the arrangement of these enzymes in the batrachoidid fishes has greater similarity to that of M. salmoides than to that of S. acanthias. However, differences within the family appear to coincide with the different nitrogen excretion strategies. O. tau and P. notatus are primarily ammoniotelic and most closely resemble the ammoniotelic M. salmoides, whereas ureotelism in O. beta is correlated with the presence of a mitochondrial glutamine synthetase and the ability to induce higher total glutamine synthetase activities than O. tau or P. notatus. Additionally, isolated mitochondria from O. beta were able to generate citrulline from glutamine, whereas those from O. tau were not. Also in contrast to S. acanthias, glutamine synthetase activities in the mitochondria of O. beta are consistently lower than those of CPSase III. This and other kinetic observations lend support to the hypothesis that glutamine synthetase may be an important regulatory control point in determining rates of ureogenesis in O. beta.

scholarly journals Inhibition of ureagenesis by valproate in rat hepatocytes. Role of N-acetylglutamate and acetyl-CoA

1983 ◽  
Vol 216 (1) ◽  
pp. 233-236 ◽  
Author(s):  
F X Coude ◽  
G Grimber ◽  
P Parvy ◽  
D Rabier ◽  
F Petit
Keyword(s):  
Rat Hepatocytes ◽  
Urea Synthesis ◽  
Carbamoyl Phosphate Synthetase ◽  
Carbamoyl Phosphate ◽  
Acetyl Coa ◽  
Isolated Rat Hepatocytes ◽  
Cellular Concentration ◽  
Acetylglutamate Synthase ◽  
Ornithine Transcarbamoylase

Valproate (0.5-5 mM) strongly inhibited urea synthesis in isolated rat hepatocytes incubated with 10 mM-alanine and 3 mM-ornithine. Valproate at the same concentrations markedly decreased concentrations of N-acetylglutamate, an essential activator of carbamoyl-phosphate synthetase I (EC 6.3.4.16), in parallel with the inhibition of urea synthesis by valproate. This compound also lowered the cellular concentration of acetyl-CoA, a substrate of N-acetylglutamate synthase (EC 2.3.1.1); glutamate, aspartate and citrulline were similarly decreased. Valproate in a dose up to 2 mM did not significantly affect the cellular concentration of ATP and had no direct effect on N-acetylglutamate synthesis, carbamoyl-phosphate synthetase I and ornithine transcarbamoylase (EC 2.1.3.3) activities.

scholarly journals Induction of carbamoyl phosphate synthetase III and glutamine synthetase mRNA during confinement stress in gulf toadfish (Opsanus beta)

2000 ◽  
Vol 203 (2) ◽  
pp. 311-320 ◽  
Author(s):  
H. Kong ◽  
N. Kahatapitiya ◽  
K. Kingsley ◽  
W.L. Salo ◽  
P.M. Anderson ◽  
...  
Keyword(s):  
Glutamine Synthetase ◽  
Waste Product ◽  
Mrna Levels ◽  
Urea Synthesis ◽  
Carbamoyl Phosphate ◽  
Confinement Stress ◽  
Actin Mrna ◽  
Mrna Analysis ◽  
Ribonuclease Protection ◽  
Gulf Toadfish

Gulf toadfish (Opsanus β) rapidly switch to excretion of urea as their main nitrogenous waste product under several laboratory conditions, including confinement to small volumes of water. Prior evidence suggested that the activities of two key enzymes of urea synthesis exhibited potentially different modes of upregulation during this switch, with carbamoyl phosphate synthethase III (CPSase III) activated allosterically by N-acetylglutamate, and glutamine synthetase (GSase) activated by increases in the concentration of protein. The present study was undertaken to examine additional aspects of the regulation of these enzymes. The sequence for O. beta CPSase III cDNA was obtained, and it was found to be similar to that of other piscine CPSases. The sequence also allowed us to develop riboprobes for CPSase III mRNA analysis using ribonuclease protection assays (RPAs). CPSase III mRNA was expressed in liver, muscle, kidney and intestine, in agreement with prior enzymatic measurements. Levels of CPSase III mRNA increased five- to tenfold (relative to beta-actin mRNA) in liver (but not muscle) following 48 h of confinement stress. Measured by western analysis using an antibody to chicken GSase, confined O. beta GSase protein concentrations increased eightfold over control levels, in agreement with prior and present measurements of increases in GSase activity. Furthermore, RPAs of GSase mRNA levels demonstrated an increase of fivefold during confinement.

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