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PubMed1973

Effects of dichloroacetate on the metabolism of glucose, pyruvate, acetate, 3-hydroxybutyrate and palmitate in rat diaphragm and heart muscle in vitro and on extraction of glucose, lactate, pyruvate and free fatty acids by dog heart in vivo.

1. The extractions of glucose, lactate, pyruvate and free fatty acids by dog heart in vivo were calculated from measurements of their arterial and coronary sinus blood concentration. Elevation of plasma free fatty acid concentrations by infusion of intralipid and heparin resulted in increased extraction of free fatty acids and diminished extractions of glucose, lactate and pyruvate by the heart. It is suggested that metabolism of free fatty acids by the heart in vivo, as in vitro, may impair utilization of these substrates. These effects of elevated plasma free fatty acid concentrations on extractions by the heart in vivo were reversed by injection of dichloroacetate, which also improved extraction of lactate and pyruvate by the heart in vivo in alloxan diabetes. 2. Sodium dichloroacetate increased glucose oxidation and pyruvate oxidation in hearts from fed normal or alloxan-diabetic rats perfused with glucose and insulin. Dichloroacetate inhibited oxidation of acetate and 3-hydroxybutyrate and partially reversed inhibitory effects of these substrates on the oxidation of glucose. In rat diaphragm muscle dichloroacetate inhibited oxidation of acetate, 3-hydroxybutyrate and palmitate and increased glucose oxidation and pyruvate oxidation in diaphragms from alloxan-diabetic rats. Dichloroacetate increased the rate of glycolysis in hearts perfused with glucose, insulin and acetate and evidence is given that this results from a lowering of the citrate concentration within the cell, with a consequent activation of phosphofructokinase. 3. In hearts from normal rats perfused with glucose and insulin, dichloroacetate increased cell concentrations of acetyl-CoA, acetylcarnitine and glutamate and lowered those of aspartate and malate. In perfusions with glucose, insulin and acetate, dichloroacetate lowered the cell citrate concentration without lowering the acetyl-CoA or acetylcarnitine concentrations. Measurements of specific radioactivities of acetyl-CoA, acetylcarnitine and citrate in perfusions with [1-(14)C]acetate indicated that dichloroacetate lowered the specific radio-activity of these substrates in the perfused heart. Evidence is given that dichloroacetate may not be metabolized by the heart to dichloroacetyl-CoA or dichloroacetylcarnitine or citrate or CO(2). 4. We suggest that dichloroacetate may activate pyruvate dehydrogenase, thus increasing the oxidation of pyruvate to acetyl-CoA and acetylcarnitine and the conversion of acetyl-CoA into glutamate, with consumption of aspartate and malate. Possible mechanisms for the changes in cell citrate concentration and for inhibitory effects of dichloroacetate on the oxidation of acetate, 3-hydroxybutyrate and palmitate are discussed.

Acetates↗
PubMed1964

EFFECT OF SALMONELLA GALLINARUM ON CERTAIN KREBS CYCLE INTERMEDIATES OF DOMESTIC FOWL.

Freeman, B. M. (Houghton Poultry Research Station, Huntingdon, England), and L. G. Chubb. Effect of Salmonella gallinarum on certain Krebs cycle intermediates of domestic fowl. J. Bacteriol. 88:93-95. 1964.-In chickens infected with Salmonella gallinarum, the citric acid content of the blood rose but that of the liver fell significantly. The former may be due solely to anorexia; the latter is suggested to be a result of the inhibition of the reaction between pyruvic and oxaloacetic acids. Pyruvic acid in the blood remained at its normal level, suggesting that other pathways for its metabolism were being utilized. A rise in the blood alpha-ketoglutaric acid concentration was also found; this appeared to be a specific response to the infection. These results are compared with data available for other species of Salmonella.

Acetates↗
PubMed1984

ATP-dependent phosphorylation of alpha-substituted carboxylic acids catalyzed by pyruvate kinase.

Pyruvate kinase from rabbit muscle catalyzes an ATP-dependent phosphorylation of glycolate to yield 2-phosphoglycolate (F. J. Kayne (1974) Biochem. Biophys. Res. Commun. 59, 8-13). An investigation of anologous reactions with other alpha-substituted carboxylic acids reveals several new substrates for such a phosphorylation reaction. Thus the alpha-hydroxy carboxylic acids L-lactate, D-lactate, DL-alpha-hydroxybutyrate, DL-alpha-hydroxyvalerate, L-glycerate, D-glycerate, DL-nitrolactate, and DL-beta-chlorolactate are phosphorylated on the alpha-hydroxy group to give the corresponding phosphoesters. Thioglycolate is also a slow substrate for phosphorylation of the thiol group to give the phosphothioglycolate, and DL-thiolactate is phosphorylated in a very slow reaction to give phosphothiolactate. beta-Hydroxypyruvate is a substrate; but, unlike the reaction with pyruvate, with beta-hydroxypyruvate the equilibrium for the reaction lies in favor of ADP and the phosphorylated product which appears from 31P NMR data to be tartronate-semialdehyde-2-phosphate. 31P NMR spectroscopy has been used to verify the identity of the products for all of the reactions. Steady-state kinetic constants have been obtained for some of the more rapid reactions. The reactions with glycolate, L-glycerate, and beta-hydroxypyruvate have kcat values that are close to that for phosphorylation of pyruvate in the reverse of the physiological reaction.

Adenosine Triphosphate↗
PubMed1981

The role of lipoic acid residues in the pyruvate dehydrogenase multienzyme complex of Escherichia coli.

Two lipoic acid residues on each dihydrolipoamide acetyltransferase (E2) chain of the pyruvate dehydrogenase multienzyme complex of Escherichia coli were found to undergo oxidoreduction reactions with NAD+ catalysed by the lipoamide dehydrogenase component. It was observed that: (a) 2 mol of reagent/mol of E2 chain was incorporated when the complex was incubated with N-ethylmaleimide in the presence of acetyl-SCoA and NADH; (b) 4 mol of reagent/mol of E2 chain was incorporated when the complex was incubated with N-ethylmaleimide in the presence of NADH; (c) between 1 and 2 mol of acetyl groups/mol of E2 chain was incorporated when the complex was incubated with acetyl-SCoA plus NADH; (d) 2 mol of acetyl groups/mol of E2 chain was incorporated when the complex was incubated with pyruvate either before or after many catalytic turnovers through the overall reaction. There was no evidence to support the view that only half of the dihydrolipoic acid residues can be reoxidized by NAD+. However, chemical modification of lipoic acid residues with N-ethylmaleimide was shown to proceed faster than the accompanying loss of enzymic activity under all conditions tested, which indicates that not all the lipoyl groups are essential for activity. The most likely explanation for this result is an enzymic mechanism in which one lipoic acid residue can take over the function of another.

Acetyl Coenzyme A↗
PubMed1993

Radiosensitization of human lung fibroblasts by chemical that decrease ATP levels.

Radiosensitization by lactate, pyruvate, nalidixic acid and novobiocin was studied in exponentially growing SH-18L human lung fibroblasts. All the chemicals had a slight radiosensitizing effect at a low concentration and a definite effect at a higher one. Decreases in the D0 and/or Dq values were present in each dose survival curve. Fibroblasts incubated with the low concentration of each chemical for 24 hrs after X irradiation showed no reduction in intracellular ATP content, whereas, the higher concentration produced a significant decrease. These observations suggest that the decrease in the ATP content may be involved in the radiosensitization of human fibroblasts at high concentrations of these chemicals. In contrast, radiosensitization at a low concentration is not explained by a relationship to ATP content. Different mechanisms may be involved in radiosensitization at low and high concentrations of these chemicals.

Adenosine Triphosphate↗