scholarly journals Altered enzyme activities and citrulline synthesis in liver mitochondria from ornithine carbamoyltransferase-deficient sparse-furash mice

1989 ◽  
Vol 257 (1) ◽  
pp. 251-257 ◽  
Author(s):  
N S Cohen ◽  
C W Cheung ◽  
L Raijman
Keyword(s):  
Protein Interactions ◽  
Mitochondrial Protein ◽  
Normal Liver ◽  
Liver Mitochondria ◽  
Synthetase Activity ◽  
Single Mutation ◽  
Ornithine Carbamoyltransferase ◽  
Carbamoyl Phosphate Synthetase ◽  
Carbamoyl Phosphate ◽  
Citrulline Synthesis

Male mice carrying the spfash mutation have 5-10% of the normal activity of ornithine carbamoyltransferase, yet are only slightly hyperammonaemic and develop quite well. A study of liver mitochondria from normal and spfash males showed that they differ in important ways. (1) The spfash liver contains about 33% more mitochondrial protein per g than does normal liver. (2) The specific activities of carbamoyl-phosphate synthetase (ammonia) and glutamate dehydrogenase are about 15% lower than normal in mitochondria from spfash mice, whereas those of beta-hydroxybutyrate dehydrogenase and cytochrome oxidase are 22% higher and 30% lower respectively. (3) In the presence of 10 mM-ornithine and the substrates for carbamoyl phosphate synthesis, coupled and uncoupled mitochondria from spfash mice synthesize citrulline at unexpectedly high rates, about 25 and 44 nmol/min per mg respectively. Though these are somewhat lower than the corresponding rates obtained with normal mitochondria, the difference does not arise from the deficiency in ornithine carbamoyltransferase, but from the lower carbamoyl-phosphate synthetase activity of the mutant mitochondria. (4) At lower external [ornithine] (less than 2 mM), a smaller fraction of the carbamoyl phosphate synthesized is converted into citrulline in spfash than in normal mitochondria. These studies show that what appears to be a single mutation brings about major adaptations in the mitochondrial component of liver. In addition, they clarify the role of ornithine transport and of protein-protein interactions in citrulline synthesis in normal mitochondria.

scholarly journals Citrulline synthesis in rat tissues and liver content of carbamoyl phosphate and ornithine

1974 ◽  
Vol 138 (2) ◽  
pp. 225-232 ◽  
Author(s):  
Luisa Raijman
Keyword(s):  
Rat Liver ◽  
Soluble Fraction ◽  
Maximal Activity ◽  
Rat Tissues ◽  
Ornithine Carbamoyltransferase ◽  
Carbamoyl Phosphate Synthetase ◽  
Carbamoyl Phosphate ◽  
Citrulline Synthesis

Rat liver ornithine carbamoyltransferase appears to be located exclusively in the mitochondria; the activity that is found in the soluble fraction is indistinguishable from mitochondrial ornithine carbamoyltransferase by simple kinetic criteria, and seems to result from breakage of mitochondria during homogenization. Of several rat tissues studied, only the liver and the mucosa of small intestine contain significant amounts of ornithine carbamoyltransferase; the activity in intestinal mucosa is less than one thousandth of that in liver. Qualitatively, this distribution coincides with that of carbamoyl phosphate synthetase I and its cofactor, acetylglutamate. The rat liver contents of carbamoyl phosphate and ornithine were 0.1 and 0.15μmol/g wet wt. of tissue respectively. On the basis of these values, it is proposed that in vivo the ornithine carbamoyltransferase activity of liver may be much lower than its maximal activity in vitro might suggest.

scholarly journals CYTOCHEMICAL DEMONSTRATION OF ORNITHINE CARBAMOYLTRANSFERASE ACTIVITY IN LIVER MITOCHONDRIA OF RAT AND MOUSE

1968 ◽  
Vol 16 (3) ◽  
pp. 172-180 ◽  
Author(s):  
AKIRA MIZUTANI
Keyword(s):  
Lead Nitrate ◽  
Liver Mitochondria ◽  
Ornithine Carbamoyltransferase ◽  
Carbamoyl Phosphate ◽  
Acid And Alkaline Phosphatase ◽  
Cytochemical Demonstration ◽  
Brush Borders ◽  
Liver And Kidney ◽  
Cold Acetone ◽  
Tris Maleate

In order to demonstrate ornithine carbamoyltransferase activity cytochemically, thin slices of liver and kidney of rat and mouse were fixed in cold acetone or formol-calcium, and incubated in a medium containing l-ornithine, carbamoyl phosphate, Tris-maleate buffer (pH 7.2), lead nitrate and sucrose. The specific reaction product occurred in the mitochondria of the hepatocytes only, and not in other cells of the liver or kidney. The specificity of the reaction was supported by the following observations. (1) The mitochondrial reaction was not obtained in sections incubated in a medium from which ornithine was omitted. (2) Other amino acids gave no reaction. (3) p-Chloromercuribenzoate suppressed the reaction. (4) The hepatocytes of chick (uricotelic) did not give the reaction. A nonspecific reaction in lysosomes and brush borders is caused probably by acid and alkaline phosphatase activities.

scholarly journals The regulation of carbamoyl phosphate synthase activity in rat liver mitochondria

1976 ◽  
Vol 154 (2) ◽  
pp. 415-421 ◽  
Author(s):  
J D. McGivan ◽  
N M. Bradford ◽  
J Mendes-Mourão
Keyword(s):  
Protein Content ◽  
Nitrogen Source ◽  
Rat Liver ◽  
Liver Mitochondria ◽  
Rat Liver Mitochondria ◽  
Urea Synthesis ◽  
Carbamoyl Phosphate ◽  
Citrulline Synthesis ◽  
Ornithine Transcarbamoylase ◽  
Phosphate Synthase

The rate at which isolated rat liver mitochondria synthesized citrulline with NH4C1 as nitrogen source was markedly dependent on the protein content of the diet. 2. Citrulline synthesis was not rate-limited by substrate concentration, substrate transport or ornithine transcarbamoylase activity under the conditions used. 3. The intramitochondrial content of an activator of carbamoyl phosphate synthase, assumed to be N-acetyl-glutamate, varied markedly with dietary protein content. The variation in the concentration of this activator was sufficient to account for the observed variation in the rates of citrulline synthesis if this synthesis were rate-limited by the activity of carbamoyl phosphate synthase. 4. The rates of urea formation from NH4Cl as nitrogen source in isolated liver cells showed variations in response to diet that closely paralleled the variations in the rates of citrulline synthesis observed in isolated mitochondria. 5. These results are consistent with the postulate that when NH4Cl plus ornithine are present in an excess, the rate of urea synthesis is regulated at the level of carbamoyl phosphate synthase activity.

scholarly journals Altered Nitrogen Balance and Decreased Urea Excretion in Male Rats Fed Cafeteria Diet Are Related to Arginine Availability

2014 ◽  
Vol 2014 ◽  
pp. 1-9 ◽  
Author(s):  
David Sabater ◽  
Silvia Agnelli ◽  
Sofía Arriarán ◽  
José-Antonio Fernández-López ◽  
María del Mar Romero ◽  
...  
Keyword(s):  
Amino Acid ◽  
Urea Cycle ◽  
Cafeteria Diet ◽  
Nitrogen Excretion ◽  
Male Rats ◽  
Synthetase Activity ◽  
Carbamoyl Phosphate Synthetase ◽  
Carbamoyl Phosphate ◽  
Urea Excretion ◽  
Dietary Nitrogen

Hyperlipidic diets limit glucose oxidation and favor amino acid preservation, hampering the elimination of excess dietary nitrogen and the catabolic utilization of amino acids. We analyzed whether reduced urea excretion was a consequence of higherNOx; (nitrite, nitrate, and other derivatives) availability caused by increased nitric oxide production in metabolic syndrome. Rats fed a cafeteria diet for 30 days had a higher intake and accumulation of amino acid nitrogen and lower urea excretion. There were no differences in plasma nitrate or nitrite.NOxand creatinine excretion accounted for only a small part of total nitrogen excretion. Rats fed a cafeteria diet had higher plasma levels of glutamine, serine, threonine, glycine, and ornithine when compared with controls, whereas arginine was lower. Liver carbamoyl-phosphate synthetase I activity was higher in cafeteria diet-fed rats, but arginase I was lower. The high carbamoyl-phosphate synthetase activity and ornithine levels suggest activation of the urea cycle in cafeteria diet-fed rats, but low arginine levels point to a block in the urea cycle between ornithine and arginine, thereby preventing the elimination of excess nitrogen as urea. The ultimate consequence of this paradoxical block in the urea cycle seems to be the limitation of arginine production and/or availability.

scholarly journals Pyrimidine nucleotide biosynthesis in Phaseolus aureus. Enzymic aspects of the control of carbamoyl phosphate synthesis and utilization

1972 ◽  
Vol 129 (3) ◽  
pp. 583-593 ◽  
Author(s):  
B. L. Ong ◽  
J. F. Jackson
Keyword(s):  
Inhibitory Effect ◽  
Aspartate Transcarbamoylase ◽  
Synthetase Activity ◽  
Carbamoyl Phosphate Synthetase ◽  
Phaseolus Aureus ◽  
Carbamoyl Phosphate ◽  
Purine Nucleotides ◽  
Nucleotide Biosynthesis ◽  
Pyrimidine Nucleotide ◽  
Ornithine Transcarbamoylase

1. Carbamoyl phosphate synthetase activity of Phaseolus aureus extracts was assayed by coupling it to the catalytic subunit of Escherichia coli aspartate transcarbamoylase and determining the [14C]carbamoylaspartate so formed. The stability of the activity was improved by the addition of ornithine and dimethyl sulphoxide to the extraction medium. 2. The synthetase activity was found to utilize either glutamine or ammonia as amino donor, the Michaelis constants being 0.17±0.03mm and 6.1±1.0mm respectively. N-Acetylglutamate did not significantly alter the rate with either substrate, and azaserine inhibited the reaction with both amino donors to the same extent. 3. Ornithine was shown to stimulate the activity, and to counteract inhibition by UMP. The purine nucleotides IMP and GMP enhanced carbamoyl phosphate formation, whereas AMP had an inhibitory effect. 4. The Michaelis constant for carbamoyl phosphate was determined in concentrated extracts for both aspartate transcarbamoylase and ornithine transcarbamoylase activities, and was 0.13±0.03mm and 1.58±0.16mm respectively. The ratio of the activities of these two enzymes, determined at near-saturating substrate concentrations, was 1:3 (aspartate transcarbamoylase/ornithine transcarbamoylase). 5. It is concluded that in this plant tissue there is one enzyme, carbamoyl phosphate synthetase, supplying carbamoyl phosphate to both the pyrimidine and arginine pathways, that the pyrimidine pathway claims most of the available carbamoyl phosphate (depending on the concentration of the nucleotide effectors) when this intermediate is present at low concentrations; and that when the carbamoyl phosphate concentration is increased, possibly by ornithine stimulation, a larger proportion can be taken up by the arginine pathway.

Mechanism of arginine protection against ammonia intoxication in the rat

1984 ◽  
Vol 247 (3) ◽  
pp. G290-G295 ◽  
Author(s):  
M. W. Goodman ◽  
L. Zieve ◽  
F. N. Konstantinides ◽  
F. B. Cerra
Keyword(s):  
Orotic Acid ◽  
Ammonia Nitrogen ◽  
Ornithine Carbamoyltransferase ◽  
Blood Ammonia ◽  
Carbamoyl Phosphate Synthetase ◽  
Acid Excretion ◽  
Carbamoyl Phosphate ◽  
Plasma Urea ◽  
Urea Content ◽  
Plasma Urea Concentration

To examine the beneficial effect of arginine on ammonia intoxication, rats were injected intraperitoneally with a single dose of NH4Cl (6.75 mmol/kg) with and without arginine (5.0 mmol/kg) or ornithine (5.0 mmol/kg). Arginine or ornithine reduced the blood ammonia nitrogen at 30 min after NH4Cl injection from 3,288 +/- 800 micrograms/dl (mean +/- SE) to 538 +/- 90 and 575 +/- 34 micrograms/dl, respectively. In rats administered this dose of NH4Cl, arginine or ornithine did not increase further the hepatic carbamoyl-phosphate synthetase (EC 6.3.4.16) activation by N-acetylglutamate beyond the effect of NH4Cl. However, arginine or ornithine did increase the hepatic citrulline and urea content as well as the plasma urea concentration in these NH4Cl-injected rats. In rats injected with four doses of NH4Cl (2.5 mmol/kg), arginine or ornithine pretreatment increased the urea excretion and normalized the orotic acid excretion. These results indicate that arginine mitigates ammonia intoxication in the rat by increasing ornithine carbamoyltransferase activity through increased ornithine availability and not via activation of N-acetylglutamate synthetase. By increasing ornithine carbamoyltransferase activity, ornithine enhances the conversion of ammonia to citrulline and urea.

Urea concentration and ornithine decarboxylase in liver of female rats

1986 ◽  
Vol 250 (4) ◽  
pp. E377-E380
Author(s):  
Y. Hitier ◽  
O. Champigny ◽  
G. Bourdel
Keyword(s):  
Ornithine Decarboxylase ◽  
Virgin Female ◽  
Fold Increase ◽  
Urea Concentration ◽  
Female Rats ◽  
Ornithine Carbamoyltransferase ◽  
Carbamoyl Phosphate Synthetase ◽  
Carbamoyl Phosphate ◽  
Pregnant Rats ◽  
Metabolizing Enzymes

In virgin female rats thioacetamide administration (1 mg/100 g body wt) induced a 16-fold increase in liver ornithine decarboxylase (ODC) activity and a significant decrease (19%) in hepatic urea concentration. The ornithine-metabolizing enzymes, ornithine-oxo-acid aminotransferase and ornithine carbamoyltransferase, were not modified by the treatment; only carbamoyltransferase, were not modified by the treatment; only carbamoyl-phosphate synthetase I activity was significantly reduced. In 19-day pregnant rats DL-alpha-difluoromethylornithine treatment inhibited the expression of enhanced ODC activity occurring normally at this stage of pregnancy. Concomitantly an inhibition of the usual decrease in hepatic urea was observed. This increase of ureagenesis occurred without any increase in liver N-acetylglutamate or ornithine concentrations, which remained as low as in normal pregnant rats.

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