SEARCH · Search PubMed

Results for “Pyruvates”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 775 records · Page 43Linked to original sources

PubMed1999

Steady-state and transient-state analysis of growth and metabolite production in a Saccharomyces cerevisiae strain with reduced pyruvate-decarboxylase activity.

Pyruvate decarboxylase is a key enzyme in the production of low-molecular-weight byproducts (ethanol, acetate) in biomass-directed applications of Saccharomyces cerevisiae. To investigate whether decreased expression levels of pyruvate decarboxylase can reduce byproduct formation, the PDC2 gene, which encodes a positive regulator of pyruvate-decarboxylase synthesis, was inactivated in the prototrophic strain S. cerevisiae CEN. PK113-7D. This caused a 3-4-fold reduction of pyruvate-decarboxylase activity in glucose-limited, aerobic chemostat cultures grown at a dilution rate of 0.10 h(-1). Upon exposure of such cultures to a 50 mM glucose pulse, ethanol and acetate were the major byproducts formed by the wild type. In the pdc2Delta strain, formation of ethanol and acetate was reduced by 60-70%. In contrast to the wild type, the pdc2Delta strain produced substantial amounts of pyruvate after a glucose pulse. Nevertheless, its overall byproduct formation was ca. 50% lower. The specific rate of glucose consumption after a glucose pulse to pdc2Delta cultures was about 40% lower than in wild-type cultures. This suggests that, at reduced pyruvate-decarboxylase activities, glycolytic flux is controlled by NADH reoxidation. In aerobic, glucose-limited chemostat cultures, the wild type exhibited a mixed respiro-fermentative metabolism at dilution rates above 0.30 h(-1). Below this dilution rate, sugar metabolism was respiratory. At dilution rates up to 0.20 h(-1), growth of the pdc2Delta strain was respiratory and biomass yields were similar to those of wild-type cultures. Above this dilution rate, washout occurred. The low micro(max) of the pdc2Delta strain in glucose-limited chemostat cultures indicates that occurrence of respiro-fermentative metabolism in wild-type cultures is not solely caused by competition of respiration and fermentation for pyruvate. Furthermore, it implies that inactivation of PDC2 is not a viable option for reducing byproduct formation in industrial fermentations.

Acetates↗

PubMed1992

Cysteinyl peptides labeled by dibromobutanedione in reaction with rabbit muscle pyruvate kinase.

The bifunctional reagent 1,4-dibromobutanedione (DBBD) reacts covalently with pyruvate kinase from rabbit muscle to cause inactivation of the enzyme at a rate that is linearly dependent on the reagent concentration, giving a second order rate constant of 444 min-1 M-1. The individual substrates phosphoenolpyruvate (with KCl), ADP, or ATP in the presence of divalent metal cation provide marked protection against inactivation suggesting that reaction occurs in the region of the active site. The limited incorporation of DBBD into pyruvate kinase was measured by reduction of the carbonyl groups of the enzyme-bound reagent using [3H]NaBH4. When pyruvate kinase was reacted with 120 microM DBBD at pH 7.0 for 50 min in the absence of protectants, 1.8 mol of tritium/mol of subunit was incorporated, whereas in the presence of phosphoenolpyruvate with KCl, only 1.0 mol of tritium was incorporated per mole of subunit. Modified peptides were isolated from tryptic digests of pyruvate kinase. Reaction of enzyme in the presence of substrate (showing no activity loss) yielded a single peptide, Asn-Ile-X1-Lys, where X1 corresponds to Cys164 of the known amino acid sequence of muscle pyruvate kinase. In the absence of protectants, reaction for 10 min (when the enzyme retained substantial activity) yielded Asn-Ile-X1-Lys as the major labeled peptide, whereas reaction for 50 min (when the enzyme was 88% inactivated) yielded predominantly Asn-Ile-X1-Lys cross-linked to X2-Asp-Glu-Asn-Ile-Leu-Trp-Leu-Asp-Tyr-Lys, where X2 corresponds to Cys151. Because activity loss correlates with the appearance of the cross-linked peptides but not with formation of Asn-Ile-X1-Lys, inactivation is likely caused by the reaction leading to the cross-link between Cys151 and Cys164. The distance between the alpha-carbons of these residues in the crystal structure is 15.5 A, whereas only 12.0 A can be spanned by the two side chains linked by a dioxobutyl group, suggesting either that pyruvate kinase undergoes a conformational change in forming the cross-link or that local rapid fluctuations in structure occur in solution to the extent of 3.5 A in this region of pyruvate kinase.

Amino Acid Sequence↗

PubMed2000

Pyruvate cycling and implications for regulation of gluconeogenesis in the insect, Manduca sexta L.

Pyruvate cycling was examined in the insect Manduca sexta L. (2-(13)C)pyruvate was injected into 5th instar larvae maintained on a semisynthetic high sucrose, low sucrose, or sucrose-free diet. Pyruvate cycling and gluconeogenesis were determined from the distribution of (13)C in blood metabolites, including trehalose, the blood sugar of insects, and alanine. Pyruvate cycling was evident from the (13)C enrichment of alanine C3, synthesized by transamination of pyruvate following carboxylation to oxaloacetate and cycling through phosphoenolpyruvate. Based on the relative (13)C enrichments of alanine C2 and C3, insects maintained on the high sucrose diet displayed higher levels of cycling than insects on the other diets. Insects on all the diets, when subsequently starved, displayed low levels of cycling. Gluconeogenesis was evident in insects on sucrose-free or low sucrose diets from the selective (13)C enrichment in trehalose. The level of gluconeogenesis relative to glycolysis was indicated by the (13)C enrichment of trehalose C6 and alanine C3, both enrichments metabolically derived in the same manner. Insects starved after maintenance on the sucrose-free or low sucrose diets remained glucogenic. Insects on the high sucrose diet were not glucogenic, and subsequent starvation did not induce gluconeogenesis. The results indicate that pyruvate kinase plays a critical role in regulating the gluconeogenic/glycolytic balance, and that inhibition of pyruvate kinase is a principal regulatory event during induction of de novo trehalose synthesis. Gluconeogenesis failed to maintain homeostatic levels of blood trehalose, supporting the conclusion that blood sugar level may be important for mediating nutrient intake. Possible factors involved in the regulation of gluconeogenesis in insects are discussed.

Animals↗

PubMed1998

Functional characteristics of pyruvate transport in Phycomyces blakesleeanus.

A saturable and accumulative transport system for pyruvate has been detected in Phycomyces blakesleeanus NRRL 1555(-) mycelium. It was strongly inhibited by alpha-cyano-4-hydroxycinnamate. l-Lactate and acetate were competitive inhibitors of pyruvate transport. The initial pyruvate uptake velocity and accumulation ratio was dependent on the external pH. The Vmax of transport greatly decreased with increasing pH, whereas the affinity of the carrier for pyruvate was not affected. The pyruvate transport system mediated its homologous exchange, which was essentially pH independent, and efflux, which increased with increasing external pH. The uptake of pyruvate was energy dependent and was strongly inhibited by inhibitors of oxidative phosphorylation and of the formation of proton gradients. Glucose counteracted the inhibitory effect of the pyruvate transport produced by inhibitors of mitochondrial ATP synthesis. Our results are consistent with a pyruvate/proton cotransport in P. blakesleeanus probably driven by an electrochemical gradient of H+ generated by a plasma membrane H+-ATPase.

Acetates↗

PubMed1999

Antioxidant properties of pyruvate mediate its potentiation of beta-adrenergic inotropism in stunned myocardium.

UNLABELLED: This study tested the hypothesis that pyruvate's antioxidant actions, particularly its enhancement of the endogenous glutathione system, mediate its potentiation of beta-adrenergic inotropism in stunned myocardium. Isolated working guinea pig hearts, metabolizing 10 m M glucose and stunned by 45 min of low flow ischemia, were treated with 5 m M pyruvate, 5 m M N-acetylcysteine (NAC) and/or 2 n M isoproterenol beginning 15 min after reperfusion. The antioxidant NAC alone did not increase cardiac power (mJ/min/g wet: 11 +/- 1 in untreated and 15 +/- 2 in NAC treated stunned hearts), but NAC potentiated the increase in power produced by 2 n M isoproterenol (isoproterenol alone: 50+/-10; NAC plus isoproterenol: 133 +/- 24). Addition of NAC doubled cyclic AMP content but lowered cytosolic phosphorylation potential by 32% in isoproterenol-stimulated hearts. Stunning decreased the glutathione antioxidant ratio (GSH/GSSG) by 68%. The antioxidant ratio was completely restored by pyruvate alone or in combination with isoproterenol, but only partially restored by isoproterenol alone. Combining isoproterenol and NAC increased the GSH/GSSG ratio by an additional 36%. The combined treatment of pyruvate and isoproterenol increased the NADPH/NADP(+) ratio almost three-fold, and produced the greatest accumulation of glucose-6-phosphate of any treatment. CONCLUSIONS: like pyruvate, the antioxidant NAC potentiated beta-adrenergic inotropism of stunned myocardium. Unlike pyruvate, NAC did not increase cellular energy reserves, thus effectively limiting its potentiation of beta-adrenergic stimulation. Thus, pyruvate's potentiation of beta-adrenergic stimulation in stunned myocardium is most likely the result of the combined effects of its antioxidant and energetic properties.

Acetylcysteine↗

PubMed2006

Anaplerosis via pyruvate carboxylase is required for the fuel-induced rise in the ATP:ADP ratio in rat pancreatic islets.

AIMS/HYPOTHESIS: The molecular mechanisms of insulin release are only partially known. Among putative factors for coupling glucose metabolism to insulin secretion, anaplerosis has lately received strong support. The anaplerotic enzyme pyruvate carboxylase is highly expressed in beta cells, and anaplerosis influences insulin secretion in beta cells. By inhibiting pyruvate carboxylase in rat islets, we aimed to clarify the hitherto unknown metabolic events underlying anaplerotic regulation of insulin secretion. METHODS: Phenylacetic acid (5 mmol/l) was used to inhibit pyruvate carboxylase in isolated rat islets, which were then assessed for insulin secretion, fuel oxidation, ATP:ADP ratio, respiration, mitochondrial membrane potential, exocytosis and ATP-sensitive K(+) channel (K(ATP)-channel) conductance. RESULTS: We found that the glucose-provoked rise in ATP:ADP ratio was suppressed by inhibition of pyruvate carboxylase. In contrast, fuel oxidation, respiration and mitochondrial membrane potential, as well as Ca(2+)-induced exocytosis and K(ATP)-channel conductance in single cells, were unaffected. Insulin secretion induced by alpha-ketoisocaproic acid was suppressed, whereas methyl-succinate-stimulated secretion remained unchanged. Perifusion of rat islets revealed that inhibition of anaplerosis decreased both the second phase of insulin secretion, during which K(ATP)-independent actions of fuel secretagogues are operational, as well as the first and K(ATP)-dependent phase. CONCLUSIONS/INTERPRETATION: Our results are consistent with the concept that anaplerosis via pyruvate carboxylase determines pyruvate cycling, which has previously been shown to correlate with glucose responsiveness in clonal beta cells. These processes, controlled by pyruvate carboxylase, seem crucial for generation of an appropriate ATP:ADP ratio, which may regulate both phases of fuel-induced insulin secretion.

Adenosine Diphosphate↗

PubMed2003

Dose-dependent effects of ethyl pyruvate in mice subjected to mesenteric ischemia and reperfusion.

OBJECTIVE: We previously showed that infusing rats with a solution of ethyl pyruvate ameliorates intestinal mucosal injury after mesenteric ischemia and reperfusion. Ethyl pyruvate also has been shown to inhibit the expression of various pro-inflammatory cytokines in several animal models of critical illness, but dose-response relationships have not been investigated. DESIGN: Anesthetized C57BL/6 mice were subjected to 60 min of mesenteric ischemia followed by 60 min of reperfusion. After 55 min of ischemia, groups of mice were treated with normal saline or graded bolus doses of ethyl pyruvate dissolved in a calcium-containing balanced salt solution. Some animals (i.e., those in the sham group) were subjected to the anesthetic, but not mesenteric ischemia/reperfusion. Gut mucosal permeability was assessed using an everted gut sac technique. SETTING: University research laboratory. MEASUREMENTS AND RESULTS: Mesenteric ischemia/reperfusion significantly increased ileal mucosal permeability to the hydrophilic macromolecule, fluorescein isothiocyanate dextran (molecular mass 4,000 Da). Whereas the lowest dose of ethyl pyruvate evaluated (17 mg/kg) had no effect on gut mucosal permeability, the two highest doses tested (50 and 150 mg/kg) significantly ameliorated the development of ischemia/reperfusion-induced mucosal hyperpermeability to about the same extent. The two highest doses of ethyl pyruvate also significantly ameliorated deficits in ileal serosal and mucosal and hepatic surface microvascular perfusion induced by mesenteric ischemia/reperfusion. Ethyl pyruvate inhibited post-ischemia/reperfusion hepatic NF-kappaB activation and TNF mRNA expression in a dose-dependent fashion. CONCLUSION: Doses of ethyl pyruvate equal to or greater than 50 mg/kg ameliorate inflammation, microvascular hypoperfusion and gut mucosal damage induced by mesenteric ischemia/reperfusion in mice.

Analysis of Variance↗

PubMed2004

An enzymatic route to produce pyruvate from lactate.

A bacterial strain of Acinetobacter sp., which was capable of enzymatic production of pyruvate from lactate, was cultured in a 5-l reactor with a basal salt medium. After 14 h of fed-batch fermentation, 9.56 g l(-1) cell concentration in the broth was obtained with 20 g l(-1) (178 mM) sodium lactate and 4 g l(-1) NH(4)Cl in the medium; and the biotransformation ability was 2.51 units ml(-1). The cells were harvested from one reactor and then used for pyruvate production from lactate in the same reactor. l-lactate at a concentration about 527 mM was almost stoichiometrically converted to pyruvate in 28 h. After a total 42 h of cell culture and biotransformation, the transformative yield was about 0.72 g g(-1) pyruvate from lactate and the rate of pyruvate production was calculated as 1.33 g l(-1) h(-1) during the process. The results suggested this simple enzymatic production of pyruvate from lactate should be a promising process and may bring a yield higher than that by microbial fermentation. By this process, the recovery of pyruvate from such a simple reaction liquid is relatively easy and inexpensive to perform.

Acinetobacter↗

PubMed2002

Expression and characterization of recombinant pyruvate kinase from Toxoplasma gondii tachyzoites.

We have cloned a cDNA encoding Toxoplasma gondii pyruvate kinase and obtained the full-length recombinant enzyme with a calculated molecular mass of 57.5 kDa. The predicted amino acid sequence of T. gondii pyruvate kinase exhibited a highest identity (63%) to that of Eimeria tenella pyruvate kinase and a lower identity of less than 25% to the pyruvate kinases from other organisms. Southern blot analysis indicated that the pyruvate kinase gene existed as a single copy in the T. gondii tachyzoite. The active recombinant enzyme contained four subunits and produced a strongly sigmoid saturation curve with phosphoenolpyruvate as the variable substrate. Fructose 1,6-diphosphate, a general activating factor of pyruvate kinase in most species, did not affect the enzyme activity. However, glucose 6-phosphate radically activated the enzyme. Fructose 2,6-diphosphate suppressed the reaction velocity at a higher concentration of phosphoenolpyruvate. These properties indicate that pyruvate kinase activity in T. gondii is regulated by unusual phosphorylated sugars.

Amino Acid Sequence↗

PubMed2005

Prevention of cataract by pyruvate in experimentally diabetic mice.

Previous studies have demonstrated that administration of pyruvate prevents cataract formation in diabetic rats. It is known that the induction of cataractous process in this case is initiated by aldose reductase (AR) catalyzed synthesis and accumulation of excessive sorbitol in the lens fibres and epithelium and their consequent osmotic hydration. Synthesis of this and other polyols is competitively inhibited by pyruvate. The objective of the present investigations was hence to determine whether pyruvate would have a similar protective effect in species where cataract formation is relatively independent of sorbitol synthesis such as in humans where the lens AR activity is extremely low, especially with glucose as a substrate. The Km of AR for glucose is known to be very high. The possible protective effect of pyruvate in the low AR models was conceived on the basis of our previous findings suggesting that it can also exert substantial antiglycating as well as antioxidant effects. The present studies have hence been conducted with mice, a species known to be low in lens AR, similar to that in humans. As stipulated, pyruvate administration has indeed been found to offer a significant protection against development of diabetic cataract in this model also. The effect correlated with the inhibition of protein glycation as well as of oxidative stress. The latter was apparent by the prevention of the loss of glutathione known to be associated with diabetes. Although there was a small but noticeable increment in the sorbitol content of the diabetic lenses, this was osmotically insignificant. Even this increase was prevented by pyruvate. The magnitude of the elevation in the contents of glycated proteins and the depression in the level of glutathione were, on the contrary, highly pronounced, suggesting a more prominent role of the latter factors. In addition, the possibility of a direct metabolic support it could offer to the tissue is also imminent by its effect on the maintenance of ATP, as shown earlier. The present studies are therefore considered more relevant to the pathogenesis of cataract in human diabetics and its possible prevention by endogenous compounds with antiglycating and antioxidant properties. Inhibition of cataract formation by pyruvate in an animal model with low lens AR, similar to that in humans, has been shown for the first time.

Animals↗

PubMed1980

Specific ligand enhancement of the affinity of E. coli pyruvate oxidase for dipalmitoyl phosphatidylcholine.

Pyruvate oxidase (pyruvate: ferricytochrome b1 oxidoreductase, EC 1.2.2.2) is a peripheral membrane flavoenzyme isolated from Escherichia coli. The enzyme catalyzes the oxidative decarboxylation of pyruvate to acetate plus CO2, and is coupled to the E. coli electron traansport chain. In vitro, pyruvate oxidase activity is measured spectrophotometrically using ferricyanide as an electron acceptor. In the presence of dipalmitoyl phosphatidylcholine or a number of other phospholipids, or detergents, the enzymatic specific activity is enhanced about 25-fold. In this paper the interaction between pyruvate oxidase and dipalmitoyl phosphatidylcholine is examined. It is demonstrated that the presence of the ligands involved in catalysis has a substantial influence on the affinity between pyruvate oxidase and dipalmitoyl phosphatidylcholine. In the absence of the substrate (pyruvate) and cofactor (thiamin pyrophosphate) there is no detectable complex formation. However, when both ligands are present, a condition which results in the reduction of the flavoprotein, the interaction between the protein and phospholipid is greatly enhanced. It is clearly shown that the protein-lipid interaction is dramatically modulated by the ligands bound at the catalytic active site on the enzyme and/or by the oxidation-reduction state of the flavin.

Centrifugation, Density Gradient↗

PubMed1990

Tissue-specific expression of rat pyruvate kinase L/chloramphenicol acetyltransferase fusion gene in transgenic mice and its regulation by diet and insulin.

We produced transgenic mice carrying about 3 kb of the 5'-flanking sequence of the rat pyruvate kinase L gene linked to the chloramphenicol acetyltransferase (CAT) structural gene. Expression of the transgene was observed only in tissues in which the endogenous L-type pyruvate kinase is expressed. Dietary glucose or insulin induced similar increases in the levels of CAT and L-type pyruvate kinase mRNAs in the liver. However, the fructose-induced level of CAT mRNA was about 3- and 6- fold lower than those of endogenous L-type pyruvate kinase mRNA in the liver and kidney, respectively, confirming our previous finding that stabilization of the transcripts of the pyruvate kinase L gene is an important regulatory step in fructose induction, especially in the kidney. Thus we conclude that all the cis-acting elements responsible for tissue-specific expression of the L-type pyruvate kinase and its stimulation by dietary components and insulin are localized in the sequence from about nucleotide -3000 to +37 in the pyruvate kinase L gene.

Animals↗

PubMed1977

Influence of the rebox state of glutathione upon pyruvate kinase in the intact erythrocyte.

1. In isolated erythrocytes the ratio of reduced to oxidized glutathione was modified by the addition of diazinedicarboxylic acid bis-dimethylamide (diamide). Incubation of erythrocytes, with a decreased GSH/GSSG ratio, resulted in an increase in [S]0.5 of pyruvate kinase of phosphoenolpyruvate as measured in haemolysates. We presume this increase to be due to oxidation of the enzyme. 2. The apparent affinity of pyruvate kinase for phosphoenolpyruvate returned to normal when the GSSG formed was reduced to GSH intracellularly. Oxidation of pyruvate kinase could also be reversed by incubation of haemolysates with reducing agents such as 2-mercaptoethanol or dithioerythritol. 3. Intracellular oxidation of pyruvate kinase caused no significant changes in the Hill coefficient (n) or Vmax of the enzyme. However, the heat stability of the oxidized enzyme was lower than normal. Lability increased with increasing oxidation of the enzyme. 4. The possible role of oxidation processes in pyruvate kinase deficiency is discussed. It is concluded that not only 'in vitro' but also in the intact erythrocyte, pyruvate kinase is sensitive to oxidizing agents and intracellular redox state. However, that a decreased GSH/GSSG ratio can be a single cause of acquired pyruvate kinase deficiency seems highly improbable.

Diamide↗

PubMed1995

An improved spectrophotometric assay of pyruvate dehydrogenase in lactate dehydrogenase contaminated mitochondrial preparations from human skeletal muscle.

In mitochondria-enriched preparations of human skeletal muscle, the measurement of pyruvate dehydrogenase activity, as determined by conventional spectrophotometric assay of NADH accumulation, is underestimated due to the oxidizing activity of the contaminating lactate dehydrogenase. Using a model reaction system consisting of varying mixtures of purified lactate and pyruvate dehydrogenases, we found that the presence of oxamate, a competitive inhibitor of the lactate dehydrogenase, allowed the measurement of a linear rate of pyruvate dehydrogenase activity without interference from lactate dehydrogenase. In the presence of 25 mM oxamate, this holds true up to a ratio of 30:1 for lactate to pyruvate dehydrogenases, respectively. A similar result was obtained when using human skeletal muscle mitochondria contaminated by lactate dehydrogenase. Rates of pyruvate dehydrogenase activity ranging from 50 to 120 nmol/min/mg protein could be routinely measured in such mitochondrial fractions. We concluded that the use of oxamate allows a spectrophotometric assay for pyruvate dehydrogenase activity to be utilized when screening for pyruvate dehydrogenase deficiency in mitochondria-enriched preparations of human skeletal muscle.

Animals↗

PubMed1983

Evidence for two distinct pyruvate kinase genes in Escherichia coli K-12.

A strain of Escherichia coli K-12 defective in pyruvate kinase F has been produced. The existence of this mutant, in conjunction with earlier results, strongly suggests that the two pyruvate kinases in this bacterium are distinct forms and not interconvertible. Either form of pyruvate kinase appeared to be equally effective in the glycolytic conversion of phosphoenolpyruvate to pyruvate. Genes specifying pyruvate kinase A and pyruvate kinase F were present on the small F-prime F506 and the locus for pyruvate kinase F was found to be at minute 36.5 on the E. coli genetic map.

Chromosome Mapping↗

PubMed1980

An investigation of pyruvate metabolism in patients with cerebellar and spinocerebellar degeneration.

This study extends previous observations of pyruvate metabolism in the spino-cerebellar degenerations by screening for abnormalities of pyruvate oxidation using the rise in blood pyruvate after an oral glucose load and examining the activity of the lipoamide dehydrogenase (LAD) moeity of the pyruvate dehydrogenase complex in the serum of 31 patients with Friedreich's ataxia, hereditary spastic ataxia and primary cerebellar degeneration. Serum LAD activity was significantly reduced in 10 Friedreich's ataxia patients when compared to controls and to 10 patients with spastic ataxia, thus confirming previous studies. Two patients with Friedreich's ataxia and 2 with primary cerebellar degeneration had abnormal blood pyruvate curves after oral glucose loading. The findings suggest that abnormal pyruvate oxidation occurs in some cases of Friedreich's ataxia and primary cerebellar degeneration and that the abnormality of pyruvate metabolism is not necessarily reflected in the serum LAD activity of these patients. The relevance of these findings to the heterogeneity of the hereditary ataxias is discussed.

Adolescent↗

PubMed1988

Effects of growth hormone on pyruvate dehydrogenase activity in intact rat liver and in isolated hepatocytes: comparison with insulin.

The effects of growth hormone and insulin on the activity of pyruvate dehydrogenase were examined in the rat, both in vivo and in isolated hepatocytes. Liver mitochondria isolated from rats killed from five to 45 minutes after injection of 50 micrograms/100 g human growth hormone (hGH) or 25 micrograms/100 g insulin displayed a significant increase in the activity of basal pyruvate dehydrogenase (38% and 48% above control at ten minutes, respectively). These changes probably result from the conversion of the phosphorylated form to the nonphosphorylated form of pyruvate dehydrogenase since total enzyme activity was unaffected. Treatment of isolated hepatocytes by hGH or insulin also led to an increase in pyruvate dehydrogenase activity which was maximal (25% above control value) at 15 minutes. Later, activation progressively decreased and was no longer detectable at 60 minutes. The concentrations of hGH or insulin required for maximal activation were 100 nmol/L and 20 nmol/L, respectively, and the concentration required for half-maximal stimulation was 2 nmol/L for both hormones. The effects of 100 nmol/L hGH and 100 nmol/L insulin on pyruvate dehydrogenase activity were not additive. Basal pyruvate dehydrogenase activity in hepatocytes exhibited linear kinetics; hGH or insulin increased the Vmax of the enzyme without changing its Km and did not affect the Vmax of the total enzyme activity. It is concluded that growth hormone is as potent and as efficient as insulin in its ability to stimulate the activity of liver pyruvate dehydrogenase, and thus may be a physiological activator of this enzyme.

Animals↗

PubMed1983

A study on the physical interaction between the pyruvate dehydrogenase complex and citrate synthase.

In this paper, physicochemical evidence is given for the association between the pyruvate dehydrogenase complex (EC 1.2.4.1) and citrate synthase (EC 4.1.3.7) with two gel chromatographic techniques with poly(ethylene glycol) co-precipitation and with ultracentrifugation. Experiments with active enzyme gel chromatography indicate that citrate synthase also associates with pyruvate dehydrogenase complex in its functioning state. Citrate synthase binds to the isolated transacetylase core of pyruvate dehydrogenase complex, but in the binding to the whole pyruvate dehydrogenase complex the two other components of the complex are also involved. One pyruvate dehydrogenase complex can bind 10-11 citrate synthase dimers, and the dissociation constant is about 5.7-6.0 microM as determined by two independent methods. The association between the pyruvate dehydrogenase complex and citrate synthase raises the possibility of the dynamic compartmentation of acetyl-CoA in the mitochondria which results in the direction of acetyl-CoA from pyruvate towards citrate.

Animals↗