scholarly journals A negative correlation between oxygen uptake and glutathione oxidation in rat liver homogenates

1969 ◽  
Vol 114 (1) ◽  
pp. 5-9 ◽  
Author(s):  
R E Pinto ◽  
W Bartley
Keyword(s):  
Steady State ◽  
Oxygen Uptake ◽  
Rat Liver ◽  
Negative Correlation ◽  
Magnesium Chloride ◽  
Glutathione Oxidation ◽  
Liver Homogenates

GSH added to rat liver homogenates inhibited respiration and increased GSSG formation approximately proportionally to the amount of GSH added; the effect was increased by added magnesium chloride. Added NADPH and citrate decreased GSSG formation and increased respiration; 6·0mm-nicotinamide prevented GSSG formation and increased respiration. There was a negative correlation between GSSG formation and oxygen uptake. It is suggested that the decrease in oxygen uptake is mainly due to GSSG concentration and also that in vivo a GSH–GSSG steady state occurs.

Glucocorticoid effects on respiration and metabolism by rat liver homogenates

1962 ◽  
Vol 202 (2) ◽  
pp. 343-346 ◽  
Author(s):  
Dennis D. Goetsch ◽  
L. E. McDonald
Keyword(s):  
Lactic Acid ◽  
Oxygen Uptake ◽  
Rat Liver ◽  
Inorganic Phosphate ◽  
Chronic Administration ◽  
Glucocorticoid Treatment ◽  
Carbohydrate Utilization ◽  
Protein Levels ◽  
Liver Homogenates ◽  
And Control

The effects of glucocorticoid administration on oxygen uptake, glucose and glycogen disappearance, lactic acid formation, and inorganic phosphate and protein levels in rat liver homogenates have been studied. A single injection of hydrocortisone, prednisolone, or 9 α-fluoroprednisolone 5 hr before sacrifice resulted in a highly significant increase in oxygen uptake by rat liver homogenates, whereas chronic administration of prednisolone daily for 7 days caused a marked inhibition in homogenate respiration. Glycolytic rate did not appear to be affected by single injections since endogenous carbohydrate utilization was similar in liver homogenates prepared from control and treated animals. Incubation of liver homogenates under aerobic conditions disclosed that inorganic phosphate levels were decreased in homogenates from corticoid-treated rats, whereas these levels were similar in treated and control liver homogenates incubated under nitrogen. Under anaerobic conditions, liver homogenates from treated rats accumulated lactic acid more rapidly than untreated liver homogenates. Glucocorticoid treatment did not appear to affect protein disappearance since no differences between protein levels in treated and untreated rat liver homogenates were detected following incubation.

scholarly journals Metabolism of inorganic sulphate in the isolated perfused rat liver. Effect of sulphate concentration on the rate of sulphation by phenol sulphotransferase

1978 ◽  
Vol 176 (3) ◽  
pp. 959-965 ◽  
Author(s):  
Gerard J. Mulder ◽  
Katja Keulemans
Keyword(s):  
Steady State ◽  
Plasma Concentration ◽  
Rat Liver ◽  
Isolated Perfused Rat Liver ◽  
Perfused Rat Liver ◽  
Perfusion Medium ◽  
Physiological Concentration ◽  
Sulphate Concentration ◽  
Inorganic Sulphate

1. The metabolism of inorganic [35S]sulphate (Na235SO4) was studied in the isolated perfused rat liver at three initial concentrations of inorganic sulphate in the perfusion medium (0, 0.65 and 1.30mm), in relation to sulphation and glucuronidation of a phenolic drug, harmol (7-hydroxy-1-methyl-9H-pyrido[3,4-b]indole). 2. [35S]Sulphate rapidly equilibrated with endogenous sulphate in the liver. It was excreted in bile and reached, at the lowest concentration in the perfusion medium, concentrations in bile that were much higher than those in the perfusion medium; at the higher sulphate concentrations, these concentrations were equal. The physiological concentration of inorganic sulphate in the liver, available for sulphation of drugs, is similar to the plasma concentration. 3. At zero initial inorganic sulphate in the perfusion medium, the rate of sulphation was very low and harmol was mainly glucuronidated. At 0.65mm-sulphate glucuronidation was much decreased and considerable sulphation took place, indicating efficient competition of conjugation by sulphation. At 1.30mm-sulphate the sulphation increased still further. 4. The results suggest that an important factor in sulphation is the relatively high Km of synthesis of adenosine 3′-phosphate 5′-sulphatophosphate (the co-substrate of sulphation) for inorganic sulphate, which is of the order of the plasma concentration of inorganic sulphate. The steady-state adenosine 3′-phosphate 5′-sulphatophosphate concentration may determine the rate of sulphate conjugation of drugs in the rat in vivo.

scholarly journals The regulation of extramitochondrial free calcium ion concentration by rat liver mitochondria

1978 ◽  
Vol 176 (2) ◽  
pp. 463-474 ◽  
Author(s):  
David G. Nicholls
Keyword(s):  
Steady State ◽  
Membrane Potential ◽  
Rat Liver ◽  
Liver Mitochondria ◽  
Weak Acid ◽  
Ion Concentration ◽  
Rat Liver Mitochondria ◽  
Free Calcium ◽  
Electrochemical Gradient

The mechanism whereby rat liver mitochondria regulate the extramitochondrial concentration of free Ca2+ was investigated. At 30°C and pH7.0, mitochondria can maintain a steady-state pCa2+0 (the negative logarithm of the free extramitochondrial Ca2+ concentration) of 6.1 (0.8μm). This represents a true steady state, as slight displacements in pCa2+0 away from 6.1 result in net Ca2+ uptake or efflux in order to restore pCa2+0 to its original value. In the absence of added permeant weak acid, the steady-state pCa2+0 is virtually independent of the Ca2+ accumulated in the matrix until 60nmol of Ca2+/mg of protein has been taken up. The steady-state pCa2+0 is also independent of the membrane potential, as long as the latter parameter is above a critical value. When the membrane potential is below this value, pCa2+0 is variable and appears to be governed by thermodynamic equilibration of Ca2+ across a Ca2+ uniport. Permeant weak acids increase, and N-ethylmaleimide decreases, the capacity of mitochondria to buffer pCa2+0 in the region of 6 (1μm-free Ca2+) while accumulating Ca2+. Permeant acids delay the build-up of the transmembrane pH gradient as Ca2+ is accumulated, and consequently delay the fall in membrane potential to values insufficient to maintain a pCa2+0 of 6. The steady-state pCa2+0 is affected by temperature, incubation pH and Mg2+. The activity of the Ca2+ uniport, rather than that of the respiratory chain, is rate-limiting when pCa2+0 is greater than 5.3 (free Ca2+ less than 5μm). When the Ca2+ electrochemical gradient is in excess, the activity of the uniport decreases by 2-fold for every 0.12 increase in pCa2+0 (fall in free Ca2+). At pCa2+0 6.1, the activity of the Ca2+ uniport is kinetically limited to 5nmol of Ca2+/min per mg of protein, even when the Ca2+ electrochemical gradient is large. A steady-state cycling of Ca2+ through independent influx and efflux pathways provides a model which is kinetically and thermodynamically consistent with the present observations, and which predicts an extremely precise regulation of pCa2+0 by liver mitochondria in vivo.

scholarly journals Hepatic Golgi fractions resolved into membrane and content subfractions.

1982 ◽  
Vol 92 (3) ◽  
pp. 822-832 ◽  
Author(s):  
K E Howell ◽  
G E Palade
Keyword(s):  
Electron Microscopy ◽  
Rat Liver ◽  
Enzyme Activities ◽  
Degree Of Contamination ◽  
Golgi Membranes ◽  
Membrane Enzyme ◽  
Biochemical Assays ◽  
The Reformation ◽  
Liver Homogenates

Golgi fractions isolated from rat liver homogenates have been resolved into membrane and content subfractions by treatment with 100 mM Na2CO3 pH 11.3. This procedure permitted extensive extraction of content proteins and lipoproteins, presumably because it caused an alteration of Golgi membranes that minimized the reformation of closed vesicles. The type and degree of contamination of the fractions was assessed by electron microscopy and biochemical assays. The membrane subfraction retained 15% of content proteins and lipids, and these could not be removed by various washing procedures. The content subfraction was contaminated by both membrane fragments and vesicles and accounted for 5 to 10% of the membrane enzyme activities of the original Golgi fraction. The lipid compositions of the subfractions was determined, and the phospholipids of both membrane and content were found to be uniformly labeled with [33P]phosphate administered in vivo.

scholarly journals Stabilization of rat liver tyrosine aminotransferase by tetracycline

1975 ◽  
Vol 150 (3) ◽  
pp. 329-333 ◽  
Author(s):  
R Hannah ◽  
M K Sahib
Keyword(s):  
Rat Liver ◽  
De Novo ◽  
Rabbit Antiserum ◽  
Tyrosine Aminotransferase ◽  
Enzyme Inactivation ◽  
Aminotransferase Activity ◽  
Rapid Inactivation ◽  
Liver Homogenates

Rat liver tyrosine aminotransferase was purified 200-fold and an antiserum raised against it in rabbits. 2. Hepatic tyrosine aminotransferase activity was increased fourfold by tyrosine, twofold by tetracycline, 2.5-fold by cortisone 21-acetate and ninefold by a combination of tyrosine and cortisol administered intraperitoneally to rats. 3. Radioimmunoassay with 14C-labelled tyrosine aminotransferase, in conjunction with rabbit antiserum against the enzyme, revealed that cortisol stimulates the synthesis of the enzyme de novo, but that tetracycline has no such effect. 4. Incubation of rat liver homogenates with purified tyrosine aminotransferase in vitro leads to a rapid inactivation of the enzyme, which tetracycline partially inhibits. 5. The inactivation is brought about by intact lysosomes, and the addition of 10mM-cysteine increases the rate of enzyme inactivation, which is further markedly increased by 10mM-Mg2+ and 10mM-ATP. Here again tetracycline partially inhibits the decay rate, leading to the inference that the increase of tyrosine aminotransferase activity in vivo by tetracycline is brought about by the latter inhibiting the lysosomal catheptic action.

Oxidative phosphorylation and adenosine triphosphatase activity in the liver mitochondria of rats administered with phenylhydrazine and hydroiyzed glucose cycloacetoacetate

1969 ◽  
Vol 47 (3) ◽  
pp. 297-300 ◽  
Author(s):  
T. G. Reddi ◽  
M. C. Nath
Keyword(s):  
Oxygen Uptake ◽  
Oxidative Phosphorylation ◽  
Rat Liver ◽  
Adenosine Triphosphatase ◽  
Liver Mitochondria ◽  
Rat Liver Mitochondria ◽  
Partial Restoration ◽  
Atp Formation

The effect of phenylhydrazine and hydroiyzed product of glucose cycloacetoacetate (GCAh) administration on the activity of adenosine triphosphatase (ATPase) in rat-liver mitochondria has been investigated. The results are discussed in relation to the efficiency of mitochondrial oxidative phosphorylation. Phenylhydrazine was found to increase the ATPase activity both in vitro and in vivo. However, preincubation or treatment with hydrolyzed glucose cycloacetoacetate resulted in an appreciable depression of this phenylhydrazine-enhanced enzyme activity. The liver mitochondria from phenylhydrazine-administered rats showed very little difference in milligrams of total protein, but the homogenates had a high protein content as compared to the preparations from normal rats and rats administered with hydrolyzed glucose cycloacetoacetate. With citrate as the substrate, normal rat-liver mitochondria exhibited a P/O ratio of 3.0. With the same substrate, the liver mitochondria from phenylhydrazine-administered rats lowered the oxygen uptake and ATP formation, thereby resulting in a decreased P/O ratio of 2.4, whereas administration of hydrolyzed glucose cycloacetoacetate prior to phenylhydrazine resulted in a partial restoration in oxygen uptake and ATP formation, and thus yielded a P/O ratio of 2.8.

scholarly journals Is the mechanism of nitroglycerin tolerance associated with aldehyde dehydrogenase activity? A contribution to the ongoing discussion

2019 ◽  
Author(s):  
Anna Bilska-Wilkosz ◽  
Magdalena Kotańska ◽  
Magdalena Górny ◽  
Barbara Filipek ◽  
Małgorzata Iciek
Keyword(s):  
Rat Liver ◽  
Aldehyde Dehydrogenase ◽  
Lipoic Acid ◽  
Total Activity ◽  
Nitrate Tolerance ◽  
Aldh Activity ◽  
Liver Homogenates ◽  
Development Of Tolerance ◽  
Aldehyde Dehydrogenase Activity

The aim of the study presented here was an attempt to answer the question posed in the title: Is the mechanism of nitroglycerin tolerance associated with aldehyde dehydrogenase (ALDH) activity? Here, we investigated the effect of administration (separately or jointly) of lipoic acid (LA), nitroglycerin (GTN), and disulfiram (DSF; an irreversible in vivo inhibitor of all ALDH isozymes (including ALDH2)), on the development of tolerance to GTN. We also assessed the total activity of ALDH in the rat liver homogenates. Our data revealed that not only DSF and GTN inhibited the total ALDH activity in the rat liver, but LA also proved to be an inhibitor of this enzyme. At the same time, the obtained results demonstrated that the GTN tolerance did not develop in GTN, DSF and LA jointly treated rats, but did develop in GTN and DSF jointly treated rats. This means that the ability of LA to prevent GTN tolerance is not associated with the total ALDH activity in the rat liver. In this context, the fact that animals jointly receiving GTN and DSF developed tolerance to GTN, and in animals that in addition to GTN and DSF also received LA such tolerance did not develop, is – in our opinion – a sufficient premise to conclude that the nitrate tolerance certainly is not caused by a decrease in the activity of any of the ALDH isoenzymes present in the rat liver, including ALDH2. However, many questions still await an answer, including the basic one: What is the mechanism of tolerance to nitroglycerin?

scholarly journals New kinetic parameters for rat liver arginase measured at near-physiological steady-state concentrations of arginine and Mn2+

1992 ◽  
Vol 283 (3) ◽  
pp. 653-660 ◽  
Author(s):  
S Maggini ◽  
F B Stoecklin-Tschan ◽  
S Mörikofer-Zwez ◽  
P Walter
Keyword(s):  
Steady State ◽  
Kinetic Parameters ◽  
Rat Liver ◽  
Urea Cycle ◽  
Hill Coefficient ◽  
Regulatory Effect ◽  
Free System ◽  
State Concentration ◽  
Good Agreement

A cytosolic cell-free system from rat liver containing the last three enzymes of the urea cycle, a number of cofactors and the substrates aspartate and citrulline was shown to synthesize urea at near-physiological rates ranging between 0.40 and 1.25 mumol/min per g of liver. This system was used to determine the kinetic parameters for arginase. With saturating amounts of Mn2+ (30 microM), arginine remained at a steady-state concentration of 5-35 microM depending on the aspartate and citrulline supply. Vmax. at micromolar arginine concentrations was between 1.10 and 1.25 mumol/min per g of liver, the K0.5 (arginine) between 6.0 and 6.5 microM and positive co-operativity was observed (Hill coefficient 2). Omission of Mn2+ caused a significant accumulation of arginine during the incubation, suggesting a regulatory effect of arginase. Under these conditions, Vmax. was 1.10-1.65 mumol/min per g of liver and the Km (arginine) increased up to 14.4-21.1 microM. The apparent Ka for Mn2+ in the presence of physiological concentrations of ATP, Mg2+ and arginine was calculated to be maximally 8 microM. Initial-velocity experiments with millimolar arginine concentrations as the direct substrate gave the following results, which are in good agreement with literature data. In the absence of Mn2+, Vmax. was 71.3 mumol/min per g of liver and the Km (arginine) 1.58 mM. With 30 microM-Mn2+, Vmax. was 69.4 mumol/min per g of liver and the Km (arginine) decreased to 0.94 mM. On the basis of our results, we propose the presence of high-affinity and low-affinity sites for arginine on rat liver arginase and postulate that alterations in arginase activity arising from changes in the concentration of arginine and of the cofactor Mn2+ may contribute to the regulation of ureagenesis in vivo.

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