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At least 973 records · Page 54Linked to original sources
PubMed1997

Effects of different carbon fluxes on G1 phase duration, cyclin expression, and reserve carbohydrate metabolism in Saccharomyces cerevisiae.

By controlled addition of galactose to synchronized galactose-limited Saccharomyces cerevisiae cultures, the growth rate could be regulated while external conditions were kept constant. By using this method, the G1 phase duration was modulated and expression of cell cycle-regulated genes was investigated. The expression of the cyclin genes CLN1 and CLN2 was always induced just before bud emergence, indicating that this event marks the decision to pass Start. Thus, G1 phase elongation was not due to a slower accumulation of the CLN1 and CLN2 mRNA levels. Only small differences in CLN3 expression levels were observed. The maximal SWI4 expression preceded maximal CLN1 and CLN2 expression under all conditions, as expected for a transcriptional activator. But whereas SWI4 was expressed at about 10 to 20 min, before CLN1 and CLN2 expression at high growth rates, this time increased to about 300 min below a particular consumption rate at which the G1 phase strongly elongated. In the slower-growing cultures, also an increase in SWI6 expression was observed in the G1 phase. The increase in G1 phase duration below a particular consumption rate was accompanied by a strong increase in the reserve carbohydrate levels. These carbohydrates were metabolized again before bud emergence, indicating that below this consumption rate, a transient increase in ATP flux is required for progression through the cell cycle. Since Start occurred at different cell sizes under different growth conditions, it is not just a certain cell size that triggers passage through Start.

Carbohydrate Metabolism↗
PubMed1997

Nitrogenase activity and regeneration of the cellular ATP pool in Azotobacter vinelandii adapted to different oxygen concentrations.

The in vivo activity of nitrogenase under aerobiosis was studied with diazotrophic chemostat cultures of Azotobacter vinelandii grown under glucose- or phosphate-limited conditions at different dilution rates (Ds, representing the growth rate mu) and different dissolved oxygen concentrations. Under steady-state conditions, the concentration as well as the cellular level of ATP increased in glucose-limited cultures when D was increased. Irrespective of the type of growth limitation or the dissolved oxygen concentration, the steady-state concentrations of ATP and of dinitrogen fixed by nitrogenase increased in direct proportion to each other. Specific rates of dinitrogen fixation as well as of the regeneration of the cellular ATP pool were compared with specific rates of cellular respiration. With glucose-limited cultures, the rate of regeneration of the ATP pool and the rate of respiration varied in direct proportion to each other. This relationship, however, was dependent on the dissolved oxygen concentration. As compared to the phosphate-sufficient control, phosphate-limited cultures exhibited the same nitrogenase activity but significantly increased respiratory activities. Rates of ATP regeneration and of cellular respiration of phosphate-limited cultures did not fit into the relationship characteristic of glucose-limited cultures. However, a linear relationship between the rates of dinitrogen fixation and ATP regeneration was identified irrespective of the type of growth limitation and the dissolved oxygen concentration. The results suggest that the ATP supply rather than cellular oxygen consumption is of primary importance in keeping nitrogenase activity in aerobic cultures of A. vinelandii.

Adenosine Triphosphate↗
PubMed1997

Kinetics of creatine kinase in an experimental model of low phosphocreatine and ATP in the normoxic heart.

To study the dependence of the forward flux of creatine kinase (CK) on its substrates and products we designed an acute normoxic model of steady-state depletion of phosphocreatine (PCr) and adenylate in the isovolumic acetate-perfused rat heart. Various concentrations of PCr and ATP were induced by prior perfusion with 2 deoxy-D-glucose in the presence of insulin. The apparent rate constant (k(f)) and the forward CK flux were measured under metabolic and contractile steady state by progressive saturation-transfer 31P nuclear magnetic resonance (NMR). At high adenylate content CK flux was constant for a twofold reduction in PCr concentration ([PCr]); CK flux was 6.3 +/- 0.6 mM/s (vs. 6.5 +/- 0.2 mM/s in control) because of a doubling of k(f). Although, at the lowest ATP concentration and [PCr], CK flux was reduced by 50%, it nevertheless always remained higher than ATP synthesis estimated by parallel oxygen consumption measurement. NMR-measured flux was compared with the flux computed under the hypothesis of CK equilibrium. CK flux could not be fully predicted by the concentrations of CK metabolites. This is discussed in terms of metabolite and CK isozyme compartmentation.

Adenosine Triphosphate↗
PubMed1982

Effects of ischemia on metabolite concentrations in dog renal cortex.

To investigate the effects of ischemia on renal metabolites, sequential slices of renal cortex were removed during 5 min of renal artery occlusion and for 5 min after release of occlusion. ATP concentrations rapidly fell during ischemia and rose during the postischemic period. Based on the rate of decline of ATP concentrations, the rate of ATP production was estimated to be 0.5 mumol ATP/g/min. This is considerably less than the rate of ATP production estimated from renal O2 consumption. During ischemia, AMP concentrations rose, confirming the activity of adenylate kinase. The control lactate/pyruvate ratio suggested that dog kidney cytosol is more reduced than the cytosol of rat liver and kidney. During ischemia, the lactate concentrations and the lactate/pyruvate ratio of dog renal cortex increased as expected, and fell after restoration of blood flow. beta-Hydroxybutyrate concentrations are considerably lower than those previously reported for rat liver and kidney. The beta-hydroxybutyrate/acetoacetate ratio was not measurable during ischemia. However, the mitochondrial redox state, calculated from the glutamate/alpha-ketoglutarate . NH+4 ratio, was similar to previous reports and this ratio appropriately changed during the ischemic and post-ischemic period.

3-Hydroxybutyric Acid↗
PubMed1982

On the mechanism of ischemia-induced mitochondrial dysfunction.

This study was designed to clarify the mechanism of ischemia-induced mitochondrial dysfunction. Anesthetized 24 dogs were divided into 4 groups, which were premedicated with saline for the controls, lipid emulsion 1 ml/kg, DL-carnitine 300 mg/kg or DL-propionylcarnitine 100 mg/kg. Myocardial mitochondria were prepared from both ischemic and non-ischemic areas after 30 min of coronary ligation and their functions, the levels of acyl-CoA and free L-carnitine were measured. In the control group, acyl-CoA level in ischemic mitochondria increased significantly compared with that in non-ischemic mitochondria. Administration of lipid emulsion further increased acyl-CoA level in ischemic mitochondria, but premedication with carnitine or propionylcarnitine prevented the elevation of acyl-CoA level by increasing free L-carnitine level in mitochondria. Ischemic mitochondrial function was disturbed in the control group and premedication with lipid accelerated the dysfunction, while premedication with carnitine or propionylcarnitine reduced the dysfunction. There was a clear reciprocal correlation (r = -0.98) between acyl-CoA level and mitochondrial function. These results indicate that accumulation of acyl-CoA is one of the important factors in ischemia-induced mitochondrial dysfunction.

Acyl Coenzyme A↗
PubMed2003

The role of uncoupling protein 2 in the development of type 2 diabetes.

Uncoupling proteins (UCP) are carriers expressed in the mitochondrial inner membrane that uncouple oxygen consumption by the respiratory chain from ATP synthesis. UCP2 is a member of the multigenic UCP family that is expressed in a wide range of tissues and organs. Possible functions of UCP2 include control of ATP synthesis, regulation of fatty acid metabolism and control of reactive oxygen species production. UCP2 expression in tissues involved in lipid and energy metabolism and mapping of the gene to a region linked to obesity and hyperinsulinemia prompted studies on the involvement of UCP2 in metabolic disorders, and especially in type 2 diabetes. In human adipose tissue and skeletal muscle, UCP2 expression is increased during fasting. The carrier was shown to be under the control of fatty acids and thyroid hormones in vivo. An upregulation has been observed in the liver during high-fat feeding and obesity. However, data in UCP2 gene knockout mice do not support a role for UCP2 in steatohepatitis. The most compelling metabolic role of UCP2 comes from studies in pancreatic beta cells. Overexpression in isolated pancreatic islets results in decreased ATP content and blunted glucose-stimulated insulin secretion. UCP2-deficient mice show an increased ATP level and an enhanced insulin secretion. Lack of UCP2 dramatically improves insulin secretion and decreases hyperglycemia in leptin-deficient mice. The role of UCP2 in the control of insulin secretion constitutes, to date, the most pertinent path to investigate in a therapeutic perspective.

Animals↗
PubMed1976

Autoregulatory shift from fructolysis to lactate gluconeogenisis in rat hepatocyte suspensions. The problem of metabolic zonation of liver parenchyma.

Hepatocytes were isolated from fed rats with glucose and insulin and freom fasted rats with glucagon in all media in an attempt to obtain cells which might be fixed preferentially in either the glycolytic or gluconeogenic state. When tested enzymatically, both "fed" and fasted" cells catalyzed glucose formation from lactate (gluconeogenesis) and lactate formation from fructose (fructolysis); lactate formation from glucose may have occurred in "fed" cells. Thus it was impossible, at least in the C3 part of the metabolic pathways between triosephosphate and pyruvate, to fix the hepatocytes in either metabolic state. The shift from glycolysis to gluconeogenesis could be investigated for the C3 part in "fasted" cells with fructose as the glycolytic and lactate as the gluconeogenic substrate. Lactate was first formed from fructose and later reutilized to a large extent. This reconsumption was blocked by the gluconeogenesis inhibitor quinolinate, both when tested enzymatically and radiochemically. Thus fructolysis was shifted to lactate gluconeogenesis. This shift at the assumed phosphoenolpyruvate/pyruvate cycle was autoregulatory, i.e. dependent on substrates and independent of circulating horomes. Maximal velocities and half saturating concentrations were determined for fructose and for lactate as substrates. The kinetic data obtained, especially the sigmoidal pattern of fructolysis, could nicely explain phenomenologically the rather sudden slow-down of lactate production and the shift to lactate consumption. The levels of the metabolites ATP, ADP, AMP, fructose bisphosphate and alanine, which control the enzymes of the assumed phosphoenolypyruvate/pyruvate cycle, were determined in the cytosol and in the mitochondria before and after the shift from fructose glycolysis to lactate gluconeogenesis. The changes observed could not explain the shift. Experiments with [14C] fructose plus unlabelled lactate and reciprocally, with unlabelled fructose plus [14C] lactate, clearly reveled that within the C3 part, glycolysis and gluconeogenesis were catalyzed simultaneously. The simultaneity of and the shift between fructolysis and gluconeogenesis by the liver cell suspension can best be explained by assuming two metabolically different types of hepatocytes rather than one type of hepatocyte with metabolically equal or different cell compartment. In vivo, the different types of hepatocytes would form a gluconeogenic and a glycolytic zone within the liver parenchyma. Since, under normal conditions, the size of these metabolic zones should remain unaltered, the shift from net glycolysis to net gluconeogenesis would be dependent primarily on substrate concentrations (autoregulation).

Adenine Nucleotides↗
PubMed1999

Role of the ADP/ATP and aspartate/glutamate antiporters in the uncoupling effect of fatty acids, lauryl sulfate, and 2, 4-dinitrophenol in liver mitochondria.

Study of the uncoupling effect of various saturated fatty acids (from caprylic to palmitic) revealed that the glutamate recoupling effect was more pronounced in the case of short chain fatty acids, whereas recoupling of mitochondria by carboxyatractylate was more effective in the case of long chain fatty acids. The overall recoupling effect, however, did not depend on the fatty acid chain length. Besides carboxyatractylate, glutamate and aspartate also exhibited a recoupling effect under uncoupling by lauryl sulfate. The uncoupling effect of lauryl sulfate was markedly weaker in the presence of DNP or laurate (but not FCCP) which were added in concentrations causing twofold increase in mitochondrial respiration. In the presence of lauryl sulfate the uncoupling action of laurate and DNP was insensitive to carboxyatractylate and glutamate. With laurate and DNP as uncouplers increasing the pH from 7.0 to 7.8 potentiated the recoupling effect of carboxyatractylate and attenuated the recoupling effect of glutamate. In the case of uncoupling by lauryl sulfate similar changes in the recoupling effect of carboxyatractylate and glutamate were observed only in the presence of 10 microM tetraphenylphosphonium. Thus, when uncoupling is induced by fatty acids, DNP, and lauryl sulfate, the ADP/ATP and aspartate/glutamate antiporters function as two parallel and independent pathways for mitochondrial membrane potential dissipation. We suggest that the role of the ADP/ATP antiporter in uncoupling includes proton capture from the intermembrane space with subsequent protonation of uncoupler anions, their transport as neutral molecules on the internal side, and deprotonation followed by proton release into the matrix and transfer of the uncoupler anion in the reverse direction. During uncoupling the aspartate/glutamate antiporter cyclically carries the uncoupler anion with simultaneous proton transfer from the intermembrane space into the matrix.

2,4-Dinitrophenol↗
PubMed2004

Effects of exogenous donor of nitric oxide-sodium nitroprusside on energy production of rat reticulocytes.

The effects of the sodium nitroprusside (SNP), a nitric oxide (NO) donor clinically used in the treatment of hypertensive emergencies on the energy production of rat reticulocytes were investigated. Rat reticulocyte-rich red blood cell suspensions were aerobically incubated without (control) or in the presence of different concentrations of SNP (0.1, 0.25, 0.5, 1.0 mM). SNP decreased total and coupled, but increased uncoupled oxygen consumption. This was accompanied by the stimulation of glycolysis, as measured by increased glucose consumption and lactate accumulation. Levels of all glycolytic intermediates indicate stimulation of hexokinase-phosphofructo kinase (HK-PFK), glyceraldehyde 3-phosphate dehydrogenase (GAPD) and pyruvate kinase (PK) activities in the presence of SNP. Due to the decrease of coupled oxygen consumption in the presence of SNP, ATP production via oxidative phosphorylation was significantly diminished. Simultaneous increase of glycolytic ATP production was not enough to provide constant ATP production. In addition, SNP significantly decreased ATP level, which was accompanied with increased ADP and AMP levels. However, the level of total adenine nucleotides was significantly lower, which was the consequence of increased catabolism of adenine nucleotides (increased hypoxanthine level). ATP/ADP ratio and adenylate energy charge level were significantly decreased. In conclusion, SNP induced inhibition of oxidative phosphorylation, stimulation of glycolysis, but depletion of total energy production in rat reticulocytes. These alterations were accompanied with instability of energy status.

Animals↗
PubMed1983

Evidence that the H+ electrochemical gradient across membranes of chromaffin granules is not involved in exocytosis.

The possibility that the large H+ electrochemical potential of chromaffin granules, the secretory granules of adrenal medullary chromaffin cells, plays an important role in exocytosis was investigated in cultures of chromaffin cells from bovine adrenal medulla. Methylamine uptake into the cells, [gamma-31P]phosphate nmr of ATP within intracellular chromaffin granules, O2 consumption of intracellular mitochondria, and MgATP-stimulated catecholamine uptake into chromaffin granules isolated from cultured chromaffin cells were assessed to determine whether various manipulations altered the H+ electrochemical gradients of intracellular chromaffin granules or mitochondria. Catecholamine secretion was not significantly altered by ammonium, methylamine, nigericin, carbonyl cyanide p-trifluoromethoxyphenylhydrazone, or dicyclohexylcarbodiimide under conditions when the pH of intracellular chromaffin granules was reduced or when granular or mitochondrial processes were uncoupled from H+ electrochemical gradients. The data indicate that the H+ electrochemical gradient across the chromaffin granule membrane does not play a role in exocytosis.

Adrenal Medulla↗
PubMed1997

Transcriptional regulation of the gltA and TLC genes in Rickettsia prowazekii growing in a respiration-deficient host cell.

The regulation of the citrate synthase (gltA) and ATP/ADP translocase (tlc) genes of the obligate intracellular bacterium, Rickettsia prowazekii, was analyzed in rickettsia-infected respiration-deficient G14 cells. The level of the gltA mRNAII and the tlc mRNA was much lower in the total RNA isolated from the infected G14 cells grown in 1 g/l glucose (low glucose, GL) medium than in that from infected G14 cells grown in 4.5 g/l glucose (high glucose, GH) medium. However, the level of the gltA mRNAI relative to 16 S rRNA was the same in GL and GH media. An increase in the level of the gltA mRNAII and the tlc mRNA could be observed as early as 2 hrs after shifting from GL to GH medium. We conclude that, under these experimental conditions, the tlc promoter and the gltA promoter P2, but not gltA promoter P1, were transcriptionally regulated.

Adenosine Diphosphate↗
PubMed1994

pH and temperature effects on kinetics of creatine kinase in aqueous solution and in isovolumic perfused heart. A 31P nuclear magnetization transfer study.

Phosphorylated metabolites concentrations and creatine kinase kinetics are measured by 31P NMR in solution and in isovolumic perfused rat hearts submitted to hypo- and hyperthermia as well as to acidosis (37 degrees C). In the organ, temperature variation from 40 to 25 degrees C induces an increase of phosphocreatine (PCr) stores, a decrease of Pi and ADP concentrations, but does not affect the ATP pool. Creatine kinase forward flux (Vfor) is gradually reduced when the temperature is lowered both in vitro and in perfused heart. In normothermic and hypothermic conditions, a relationship is found between cardiac performance (rate pressure product, RPP), Vfor and ATP synthesis estimated through the myocardial oxygen consumption rate (MVO2). At 40 degrees C however, the RPP is reduced although both Vfor and MVO2 increase. In vitro experiments show an optimum pH of 7.7 for the forward creatine kinase reaction. In perfused heart submitted to acidosis, a decrease of PCr concentration is observed, whereas ATP and ADP contents remain unchanged. Heart creatine kinase flux increased as in hyperthermia. These high fluxes are attributed to the coupling of the creatine kinase reaction with energy consuming or producing reactions: the increase of energy demand related to non-contractile processes could explain the high MVO2 and Vfor observed in those conditions.

Adenosine Triphosphate↗
PubMed1995

Characteristics of Fe(II)ATP complex-induced damage to the rat liver mitochondrial membrane.

It is well established that several iron complexes can induce oxidative damage in hepatic mitochondrial membranes by catalyzing the formation of OH radicals and/or by promoting lipid peroxidation. This is a relevant process for the molecular basis of iron overload diseases. The present work demonstrates that Fe(II)ATP complexes (5-50 microM) promote an oxygen consumption burst in a suspension of isolated rat liver mitochondria (either in the absence or presence of Antimycin A), caused mainly by lipid peroxidation. Fe(II)ATP alone induced small levels of oxygen uptake but no burst. The time course of Fe(II)ATP oxidation to Fe(II)ATP in the extramitochondrial media also reveals a simultaneous 'burst phase'. The iron chelator Desferal (DFO) or the chain-break antioxidant butylated hydroxytoluene (BHT) fully prevented both lipid peroxidation (quantified as oxygen uptake burst) and mitochondrial swelling. DFO and BHT were capable of stopping the ongoing process of peroxidation at any point of their addition to the mitochondrial suspension. Conversely, DFO and BHT only halted the Fe(II)ATP-induced mitochondrial swelling at the onset of the process. Fe(II)ATP could also cause the collapse of mitochondrial potential, which was protected by BHT if added at the onset of the damaging process. These results, as well as correlation studies between peroxidation and mitochondrial swelling, suggest that a two phase process is occurring during Fe(II)ATP-induced mitochondrial damage: one dependent and another independent of lipid peroxidation. The involvement of lipid peroxidation in the overall process of mitochondrial membrane injury is discussed.

Adenosine Triphosphate↗
PubMed2002

5'-p-Fluorosulfonylbenzoyl adenosine inhibits progesterone synthesis in human placental mitochondria.

The human placental mitochondria have an ATP-diphosphohydrolase (apyrase) activity. In this paper we characterized the effect of 5'-p-fluorosulfonylbenzoyl adenosine (FSBA) on placental apyrase, and its repercussion on progesterone synthesis and oxygen consumption. Apyrase activity was inhibited by FSBA. Nucleosides tri- and diphosphates protected against FSBA inactivation, but divalent cations did not, indicating that FSBA attaches itself to an ATP-binding site of apyrase. In mitochondria, the inactivation of apyrase by FSBA was associated with inhibition of progesterone synthesis. Also, the oxygen consumption induced by ATP but not by ADP, was inhibited, clearly showing that FSBA exclusively inactivated the apyrase in human placental mitochondria. It is concluded that the apyrase activity is closely related to progesterone synthesis, probably associated with the cholesterol transport between mitochondrial membranes.

Adenosine↗
PubMed1977

Effects of bilirubin on red cell metabolism.

Blirubin causes certain defects in erythrocyte metabolism, mainly in glycolysis. These effects of bilirubin were studied in vitro using a relatively physiological assay medium, which consisted of heparinized whole blood. Bilirubin was added in a small quantity of NaOH solution. In the presence of bilirubin a reduced glucose consumption of red cells and an accelerated depletion in the ATP and glycerate-2,3-bisphosphate concentration was found. Bilirubin levels lower than 50 mumol/l did not influence the glucose consumption. In agreement to other investigations it was established that bilirubin causes haemolysis of red cells. ATP-deficient cells are more sensitive to this effect.

Adenosine Triphosphate↗
PubMed1990

31P NMR studies of ATP concentrations and Pi-ATP exchange in the rat kidney in vivo: effects of inhibiting and stimulating renal metabolism.

Previous investigators found that cyanide (CN-) is a potent inhibitor of renal Na+ transport, while the uncoupling agent 2,4-dinitrophenol (DNP) and fructose (both which lower ATP levels) are weak transport inhibitors. To examine the disparate effects of these substances measurements of ATP were performed, using 31P NMR, while simultaneously monitoring renal Na+ transport. Infusion of CN-, DNP, and fructose lowered whole kidney ATP levels by about the same extent (30%) while only CN- inhibited Na+ transport. This may be due to the fact that CN- has a potent action on the thick ascending limb of Henle, while fructose and DNP may have a more proximal action. Alternatively, ATP turnover may be a more important determinant of transport than ATP concentrations. Saturation transfer experiments were performed to measure Pi-ATP flux. Unilateral nephrectomy, high protein feeding, and methylprednisolone were used to stimulate metabolism and transport. The rate of Pi-ATP flux was 20.1 mumol/min/g. However, because oxygen consumption was stimulated, the ATP/O ratio was 0.85, considerably less than the theoretical value of 3. Finally, atrial natriuretic factor, which increased Na+ transport, had no effect on Pi-ATP flux. The results raise the possibility that the saturation transfer technique does not detect all Pi-ATP flux, especially when renal metabolism is stimulated.

2,4-Dinitrophenol↗