scholarly journals Inhibition of carbamoyl-phosphate synthase (ammonia) by Tris and Hepes. Effect on Ka for N-acetylglutamate

1987 ◽  
Vol 243 (1) ◽  
pp. 273-276 ◽  
Author(s):  
P Lund ◽  
D Wiggins
Keyword(s):  
Rat Liver ◽  
Phosphate Buffer ◽  
Active Enzyme ◽  
Urea Synthesis ◽  
Carbamoyl Phosphate ◽  
A Value ◽  
Phosphate Synthase

The apparent Ka for N-acetylglutamate of rat liver carbamoyl-phosphate synthase is 11 microM in phosphate buffer, a value 10-fold lower than reported in other buffer systems. Tris and Hepes inhibit competitively with N-acetylglutamate. The proportion of carbamoyl-phosphate synthase in the active enzyme-acetylglutamate complex in vivo may be higher than previous calculations suggest, which re-opens the question of the involvement of N-acetylglutamate in the regulation of urea synthesis.

Autophagy of mitochondria in rat liver assessed by immunogold procedures.

1988 ◽  
Vol 36 (11) ◽  
pp. 1433-1440 ◽  
Author(s):  
E Knecht ◽  
A Martinez-Ramón ◽  
S Grisolia
Keyword(s):  
Glutamate Dehydrogenase ◽  
Rat Liver ◽  
Polyclonal Antibodies ◽  
Carbamoyl Phosphate ◽  
Autophagic Vacuoles ◽  
The Difference ◽  
In Vivo Administration ◽  
Phosphate Synthase

Glutamate dehydrogenase and carbamoyl phosphate synthase-I were localized in rat liver by immunogold procedures, using monoclonal and polyclonal antibodies. As expected, there was extensive labeling in mitochondria. Label was also found in lysosomal autophagic vacuoles. When autophagy was stimulated by in vivo administration of the anti-microtubular agent vinblastine we found that: (a) carbamoyl phosphate synthase-I and glutamate dehydrogenase could be found in mitochondria within autophagic vacuoles; (b) the carbamoyl phosphate synthase-I and glutamate dehydrogenase content of the mitochondria sequestered into autophagic vacuoles is the same as that of the nearby "free" mitochondria; and (c) in the whole liver, autophagic vacuoles contain c. 1.5 times more glutamate dehydrogenase than carbamoyl phosphate synthase-I, in contrast to mitochondria which have c. three times more carbamoyl phosphate synthase-I than glutamate dehydrogenase. The latter finding could explain, at least partially, the difference in half-lives of these enzymes.

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 The molecular weights of two forms of carbamoyl phosphate synthase from rat liver

1972 ◽  
Vol 127 (3) ◽  
pp. 503-508 ◽  
Author(s):  
R. Virden
Keyword(s):  
Molecular Weight ◽  
Concentration Dependence ◽  
Rat Liver ◽  
Chemical Equilibrium ◽  
High Speed ◽  
Carbamoyl Phosphate ◽  
Molecular Weights ◽  
A Value ◽  
Equilibrium Sedimentation ◽  
Phosphate Synthase

1. N-Acetylglutamate-dependent carbamoyl phosphate synthase from rat liver was centrifuged in sucrose density gradients. The concentration-dependence of s was consistent with a chemical equilibrium existing between the 11S and 7.5S forms of the enzyme. 2. Under conditions favouring the 11S form, the properties of the enzyme in ultra-short-column equilibrium experiments suggest a molecular weight of 316000±42000 for the 11S form. 3. Under conditions favouring the 7.5S form, high-speed equilibrium-sedimentation measurements gave a value of 160000±10000 as the molecular weight of the 7.5S form of the enzyme.

Regulation of urea synthesis by acid-base balance in vivo: role of NH3 concentration

1987 ◽  
Vol 252 (2) ◽  
pp. F221-F225 ◽  
Author(s):  
S. Cheema-Dhadli ◽  
R. L. Jungas ◽  
M. L. Halperin
Keyword(s):  
Ammonium Concentration ◽  
Urea Synthesis ◽  
Carbamoyl Phosphate ◽  
Acid Base Balance ◽  
Acid Base ◽  
Fixed Rate ◽  
Rate Limiting Step ◽  
Base Balance

The purpose of this study was to clarify how changes in acid-base balance influence the rate of urea synthesis in vivo. Since ureagenesis was increased by an ammonium infusion into rats, regulation seemed to be a function of the blood ammonium concentration. The rate of urea synthesis was constant at a fixed rate of ammonium infusion and independent of the conjugate base infused, chloride or bicarbonate. The steady-state blood ammonium concentration was higher in the rats that developed metabolic acidosis. Thus it appeared that regulation was not directly mediated by this ammonium concentration per se. The rate of urea synthesis was also independent of the blood pH. Accordingly, the rate of urea synthesis was examined as a function of the plasma NH3 concentration. The rate of ureagenesis was found to be directly proportional to the plasma NH3 concentration. Assuming that plasma NH3 levels reflect those in mitochondria, the NH3 concentration yielding half-maximal rates of urea synthesis (close to 2 microM) was in the same range as Km for the rate-limiting step in ureagenesis, carbamoyl phosphate synthetase (EC 6.3.4.16). These results suggest that, at a constant ammonium concentration, the decreased rate of ureagenesis caused by a pH fall in vitro could reflect an acidosis-induced decline in the concentration of true substrate (NH3) for this pathway.

scholarly journals Measurement of protein turnover in rat liver. Analysis of the complex curve for decay of label in a mixture of proteins

1976 ◽  
Vol 156 (3) ◽  
pp. 657-663 ◽  
Author(s):  
P J Garlick ◽  
J C Waterlow ◽  
R W Swick
Keyword(s):  
Rat Liver ◽  
Turnover Rate ◽  
Decay Curve ◽  
Specific Radioactivity ◽  
Liver Protein ◽  
Turnover Rates ◽  
A Value ◽  
Maximum Value ◽  
Single Exponential

The curve for decay of 14C in rat liver protein labelled by injection of NaH14CO3 was analysed to obtain the average turnover rate of mixed liver protein. Three different methods of analysis were used. (1) Unlike decay curves from homogeneous proteins, the curve did not fit a single exponential, but a good fit was obtained with three exponentials. By assuming that the mixture contained three major components with different turnover rates, the calculated value for the average turnover rate (k) was close to 40% per day. (2) k was also calculated from the area under the decay curve, a method which makes no assumptions about the number of proteins in the mixture. This method also gave a value close to 40% per day. (3) It was shown empirically, both by simulation of decay of label in model mixtures of protein and with the decay curve measured in vivo, that k can be calculated from the time taken for the specific radioactivity to fall to 10% of its maximum value. This is an advantage, since the other two methods require the decay curve to be measured over a much longer period of time.

scholarly journals Studies on the activation of rat liver pyruvate dehydrogenase and 2-oxoglutarate dehydrogenase by adrenaline and glucagon. Role of increases in intramitochondrial Ca2+ concentration

1985 ◽  
Vol 231 (3) ◽  
pp. 597-608 ◽  
Author(s):  
J G McCormack
Keyword(s):  
Rat Liver ◽  
Pyruvate Dehydrogenase ◽  
Liver Mitochondria ◽  
Active Enzyme ◽  
Female Rats ◽  
Rat Liver Mitochondria ◽  
Na Ions ◽  
Oxoglutarate Dehydrogenase

The administration in vivo of either adrenaline or glucagon alone resulted in increases of about 2-fold in the amounts of active, non-phosphorylated, pyruvate dehydrogenase in the livers of fed male or female rats, whereas when administered together increases of about 4-fold were obtained. Ca2+-dependent increases in the amount of active enzyme of up to about 5-fold could be achieved in isolated rat liver mitochondria by incubating them with increasing extramitochondrial [Ca2+]; from this, two conditions of Ca loading were chosen which caused increases in active enzyme similar to those with the hormone treatments given above. The increases in enzyme activity owing to these Ca loads persisted through the ‘re-isolation’ of mitochondria and their incubation in Na+-free KCl-based media containing EGTA. Differences from values obtained with unloaded controls could be diminished by adding Na+ ions to cause the egress of Ca2+ from the mitochondria, or enough extramitochondrial Ca2+ to saturate the enzyme in its Ca2+-dependent activation; the effects of Na+ could be blocked by diltiazem, an inhibitor of mitochondrial Na+/Ca2+ exchange. The re-isolated, Ca-preloaded, mitochondria also exhibited enhanced activities of 2-oxoglutarate dehydrogenase when assayed at non-saturating [2-oxoglutarate] by two different methods; effects of Na+, Ca2+ or diltiazem on the persistent activations of this enzyme were similar to those for pyruvate dehydrogenase. Na+ caused a marked depletion, which could be blocked by diltiazem, of the 45Ca content of re-isolated mitochondria which had pre-loaded with Ca, containing 45Ca, to the same degrees as above. The activities of pyruvate dehydrogenase and 2-oxoglutarate dehydrogenase in incubated liver mitochondria prepared from rats subjected to the hormone treatments given above were found to behave in a very similar manner to those exhibited in the re-isolated, Ca-preloaded, mitochondria. It is concluded that these hormones each bring about the activations of these rat liver enzymes by causing increases in intramitochondrial [Ca2+], and that their effects, as such, are additive.

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.

Sign in / Sign up

Export Citation Format

Share Document