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 595 records · Page 33Linked to original sources

PubMed1979

The physiological role of pyruvate carboxylation in hamster brown adipose tissue.

1. Pyruvate carboxylase is present in brown adipose tissue mitochondria. 2. In isolated mitochondria, pyruvate, bicarbonate and ATP, the substrates for pyruvate carboxylase, are able to replace added malate in supplying a condensing partner for acetyl-CoA formed from beta-oxidation of fatty acids. 3. In brown adipocytes, pyruvate and CO2 increase the rate of norepinephrine-stimulated respiration synergistically. 4. The norepinephrine-stimulated respiration in brown adipocytes is diminished when pyruvate transport into the mitochondria is inhibited. 5. Pyruvate carboxylation increases the intramitochondrial level of citric acid cycle intermediates, as shown by titrations of malonate inhibition of respiration. 6. Pyruvate carboxylation can continuously supply the mitochondria with citric acid cycle intermediates, as evidenced by its ability to maintain respiration when oxoglutarate conversion to glutamate is stimulated. 7. Pyruvate carboxylation is necessary for maximal oxygen consumption even when drainage of the citric acid cycle for amino acid synthesis is eliminated. 8. Pyruvate carboxylation explains observed effects of CO2 on respiration in brown adipocytes, and may also explain the increased glucose uptake by brown adipose tissue during thermogenesis in vivo.

Adipose Tissue, Brown↗

PubMed1998

Antibodies to pyruvate dehydrogenase in primary biliary cirrhosis: correlation with histology.

Antimitochondrial antibodies to pyruvate dehydrogenase are the hallmark of primary biliary cirrhosis. Their pathogenic role has not been proven, although antibodies to pyruvate dehydrogenase are bound to biliary epithelium. The aim of this study was to characterize serum IgA antibodies to pyruvate dehydrogenase and to evaluate their response to different treatment regimens. We also compared the level of antibodies with severity of histological lesions and the data of biochemical liver tests. Serum samples were collected at baseline and after 24 months from 61 primary biliary cirrhosis patients, whereas 23 patients were treated with ursodeoxycholic acid, 20 with colchicine, and 18 with placebo. ELISA was used to detect antibodies to pyruvate dehydrogenase. IgA and IgG were separated with jacalin and protein-A, respectively. Capacity of immunoglobulins to inhibit enzymatic activity was detected by spectrophotometric observation of the rate of enzyme reaction. 49 (80.3%) of the 61 patients possessed IgA antibodies to pyruvate dehydrogenase. Significant decrease in IgA antibodies was observed only in the ursodeoxycholic acid group (p<0.05). 15 of 18 IgA preparations and all 24 IgG preparations of patients' sera were inhibitory towards pyruvate dehydrogenase (mean inhibitory percent +/-SD: 42+/-33.4% and 79+/-22.4%, respectively, at a protein concentration of 100 microg/ml). The level of serum antibodies to pyruvate dehydrogenase correlated with several histological parameters (fibrosis, inflammatory infiltrate), but not with biochemical parameters. Our data reveal that IgA antibodies to pyruvate dehydrogenase inhibit enzyme function. The correlation between antibodies to pyruvate dehydrogenase and histological parameters might suggest the pathogenic role of these antibodies.

Adult↗

PubMed2003

Pyruvate and citric acid cycle carbon requirements in isolated skeletal muscle mitochondria.

Carbohydrate depletion precipitates fatigue in skeletal muscle, but, because pyruvate provides both acetyl-CoA for mainline oxidation and anaplerotic carbon to the citric acid cycle (CAC), the mechanism remains obscure. Thus pyruvate and CAC kinetic parameters were independently quantified in mitochondria isolated from rat mixed skeletal muscle. Mitochondrial oxygen consumption rate (Jo) was measured polarographically while either pyruvate or malate was added stepwise in the presence of a saturating concentration of the other substrate. These substrate titrations were carried out across a physiological range of fixed extramitochondrial ATP free energy states (DeltaGP), established with a creatine kinase energy clamp, and also at saturating [ADP]. The apparent Km,malate for mitochondrial Jo ranged from 21 to 32 microM, and the apparent Km,pyruvate ranged from 12 to 26 microM, with both substrate Km values increasing as DeltaGP declined. Vmax for both substrates also increased as DeltaGP fell, reflecting thermodynamic control of Jo. Reported in vivo skeletal muscle [malate] are >10-fold greater than the Km,malate determined in this study. In marked contrast, the K(m,pyruvate) determined is near the [pyruvate] reported in muscle approaching exhaustion associated with glycogen depletion. When data were evaluated in the context of a linear thermodynamic force-flow (DeltaGP-Jo) relationship, the DeltaGP-Jo slope was essentially insensitive to changes in [malate] in the range observed in vivo but decreased markedly with declining [pyruvate] across the physiological range. Mitochondrial respiration is particularly sensitive to variations in [pyruvate] in the physiological range. In contrast, physiological [malate] exerts very little, if any, influence on mitochondrial pyruvate oxidation measured in vitro.

Animals↗

PubMed2003

Differential modulation of glucose, lactate, and pyruvate oxidation by insulin and dichloroacetate in the rat heart.

Despite the fact that lactate and pyruvate are potential substrates for energy production in vivo, our understanding of the control and regulation of carbohydrate metabolism is based principally on studies where glucose is the only available carbohydrate. Therefore, the purpose of this study was to determine the contributions of lactate, pyruvate, and glucose to energy production in the isolated, perfused rat heart over a range of insulin concentrations and after activation of pyruvate dehydrogenase with dichloroacetate (DCA). Hearts were perfused with physiological concentrations of [1-13C]glucose, [U-13C]lactate, [2-13C]pyruvate, and unlabeled palmitate for 45 min. Hearts were freeze clamped, and 13C NMR glutamate isotopomer analysis was performed on tissue extracts. Glucose, lactate, and pyruvate all contributed significantly to myocardial energy production; however, in the absence of insulin, glucose contributed only 25-30% of total pyruvate oxidation. Even under conditions where carbohydrates represented >95% of substrate entering the tricarboxylic acid (TCA) cycle, we found that glucose contributed at most 50-60% of total carbohydrate oxidation. Despite being present at only 0.1 mM, pyruvate contributed between approximately 10% and 30% of total acetyl-CoA entry into the TCA cycle. We also found that insulin and DCA not only increased glucose oxidation but also exogenous pyruvate oxidation; however, lactate oxidation was not increased. The differential effects of insulin and DCA on pyruvate and lactate oxidation provide further evidence for compartmentation of cardiac carbohydrate metabolism. These results may have important implications for understanding the mechanisms underlying the beneficial effects of increasing cardiac carbohydrate metabolism.

Acetyl Coenzyme A↗

PubMed1999

Intravenous pyruvate prolongs survival during hemorrhagic shock in swine.

Pyruvate improves cellular and organ function during hypoxia and ischemia and stabilizes the NADH redox state and cytosolic ATP phosphorylation potential. In this in vivo study, we evaluated the effects of intravenous pyruvate on cardiovascular and neocortical function, indexes of the cytosolic redox state (lactate/pyruvate ratio, L/P) and cellular energy state (adenosine and degradative products hypoxanthine and inosine, ADO + HX + Ino) during controlled arterial hemorrhage (40 mmHg) in sedated swine (45 kg). Na+ pyruvate was infused 1 h before (1 g. kg(-1). h(-1)) and 2 h during (0.5 g. kg(-1). h(-1)) hemorrhage to attain arterial pyruvate levels of 6 mM. Volume (0.9% NaCl) and osmotic (10% NaCl) effects were matched in controls. Time to peak hemorrhage (57 min) and peak hemorrhage volume (43 ml/kg) were similar in all groups. The volume and osmotic groups experienced spontaneous cardiovascular decompensation between 60 and 90 min, with an average time until death of 82.7 +/- 5.5 and 74.8 +/- 8.2 min. In contrast, survival in the pyruvate group was 151.2 +/- 10.0 min (P < 0.001). During hemorrhage, the pyruvate group had better cardiovascular and cerebrovascular function with significantly higher systemic and cerebral oxygen consumption and less attenuation of the amplitude and frequency of the electrocorticogram. In addition, pyruvate prevented metabolic acidosis and stabilized the L/P. Pyruvate slowed the rise in neocortical microdialysis levels of ADO + HX + Ino, and prevented the net efflux of ADO + HX + Ino into the sagittal sinus. The findings reveal considerable metabolic and functional enhancement by pyruvate during severe hemorrhagic shock with a 75-min delay in spontaneous cardiovascular decompensation and death.

Animals↗

PubMed2001

Effects of augmented delivery of pyruvate on myocardial high-energy phosphate metabolism at high workstate.

This study was performed to determine whether the fall in myocardial high-energy phosphates (HEP) that occurs during high workstates can be ascribed to either inadequate glycolytic pyruvate generation and conversion to acyl-CoA or limitation of long-chain fatty acid transport into the mitochondria. This was tested by using infusions of either pyruvate or butyrate in anesthetized dogs. Pyruvate was used because it bypasses the glycolytic sequence of reactions, activates pyruvate dehydrogenase, and increases mitochondrial NADH concentration ([NADH(m)]) in isolated myocardium, whereas butyrate enters the mitochondria without need for transport by the rate-limiting, palmitoyl-carnitine transporter. Increasing blood pyruvate from 0.16 +/- 0.016 mM to >3 mM did not alter baseline HEP levels determined with (31)P nuclear magnetic resonance, but caused an increase in the rate-pressure product and a modest increase in myocardial oxygen consumption (MVO(2)). Infusion of dobutamine + dopamine (each 20 microg x kg(-1) x min(-1) iv) increased MVO(2) and caused decreases of myocardial phosphocreatine (PCr)/ATP. Pyruvate partially reversed the decrease of HEP levels produced by catecholamine stimulation, whereas butyrate had no effect. Neither pyruvate nor butyrate caused an increase of MVO(2) during catecholamine infusion. Deoxymyoglobin was not detected by (1)H magnetic resonance spectroscopyy in any group. The data demonstrate that carbon substrate availability to the mitochondria is not the only cause of the reduction of PCr/ATP that occurs at high workstates. Supplemental pyruvate (but not butyrate) attenuated the reduction of PCr/ATP during the high workstates; this may have resulted from direct effects on intermediary metabolism or from other effects such as the free radical scavenging activity of pyruvate.

Adenosine Triphosphate↗

PubMed2006

SLC5A8 triggers tumor cell apoptosis through pyruvate-dependent inhibition of histone deacetylases.

Tumor cells up-regulate glycolysis but convert pyruvate into lactate instead of oxidizing it. Here, we show that pyruvate, but not lactate, is an inhibitor of histone deacetylases (HDAC) and an inducer of apoptosis in tumor cells and that SLC5A8, a Na(+)/monocarboxylate cotransporter, is obligatory for this process. We found that SLC5A8 is expressed in nontransformed breast epithelial cell lines but silenced by DNA methylation in tumor cell lines. The down-regulation of the gene is also evident in primary breast tumors. When MCF7 breast tumor cells are transfected with SLC5A8 cDNA, the cells undergo pyruvate-dependent apoptosis. Butyrate and propionate also induce apoptosis in SLC5A8-expressing cells, whereas lactate does not. The differential ability of these monocarboxylates to cause apoptosis in SLC5A8-expressing MCF7 cells correlates with their ability to inhibit HDACs. Apoptosis induced by SLC5A8/pyruvate in MCF7 cells is associated with up-regulation of p53, Bax, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), TRAIL receptor (TRAILR) 1, and TRAILR2 and down-regulation of Bcl2 and survivin. Lactate dehydrogenase isozymes are differentially expressed in nontransformed cells and tumor cells such that the latter convert pyruvate into lactate. Silencing of SLC5A8 coupled with conversion of pyruvate into lactate in tumor cells correlates with increased HDAC activity in these cells compared with nontransformed cells. Our studies thus identify pyruvate as a HDAC inhibitor and indicate that the Na(+)-coupled pyruvate transport underlies the tumor-suppressive role of SLC5A8. We propose that tumor cells silence SLC5A8 and convert pyruvate into lactate as complementary mechanisms to avoid pyruvate-induced cell death.

Apoptosis↗

PubMed1976

Apparent co-operative effect of hydrogen carbonate (HCO-3) on pigeon kidney pyruvate carboxylase.

Kinetic methods have been used to determine the interrelationship between HCO-3, pyruvate and acetyl-CoA and their effect on pigeon kidney pyruvate carboxylase (pyruvate: CO2 ligase [ADP], EC 6.4.1.1). HCO-3 shows a negative co-operative effect (biphasic kinetics with two different Km values). Pyruvate influences the attachment of HCO-3 to this enzyme. The same has been shown for acetyl-CoA. Contrary to the results of other investigators no co-operative effect was seen with pyruvate even at different concentrations of acetyl-CoA. HCO-3 itself shows hardly any effect on the homotropic positive co-operativity (sigmoidal kinetics) of acetyl-CoA. The negative co-operative effect of HCO-3 could not be removed even at saturating concentrations of pyruvate and/or acetyl-CoA, which is also supported by the n and Rs values. The results of this communication bring out differences between pigeon kidney pyruvate carboxylase and pyruvate carboxylase from other sources. It is also suggested that there may be different allosteric and regulatory sites for acetyl-CoA, HCO-3 and pyruvate.

Acetyl Coenzyme A↗

PubMed2002

Influence of pyruvate on contractile performance and Ca(2+) cycling in isolated failing human myocardium.

BACKGROUND: Application of pyruvate was shown to improve contractile function in isolated animal myocardium and hemodynamics in patients with congestive heart failure. We assessed the influence of pyruvate on systolic and diastolic myocardial function and its subcellular mode of action in isolated myocardium from end-stage failing human hearts. METHODS AND RESULTS: In muscle strip preparations, concentration-dependent effects of pyruvate on developed and diastolic force (n=6), aequorin light emission reflecting intracellular Ca(2+) transients (n=6), and rapid cooling contractures reflecting sarcoplasmic reticulum (SR) Ca(2+) content (n=11) were measured. Pyruvate resulted in a concentration-dependent increase in developed force and a decrease in diastolic force, with a maximum effect of 155% and 21%, respectively, at 20 mmol/L pyruvate (P<0.05). This was associated with a dose-dependent prolongation of time to peak tension and relaxation time. Pyruvate increased rapid cooling contractures by 51% and aequorin light signals by 85% (at 15 and 20 mmol/L; P<0.05). This indicates increased SR Ca(2+) content and increased intracellular Ca(2+) transients. The inotropic effect of pyruvate was still present after elimination of SR Ca(2+) storage function with 10 micromol/L cyclopiazonic acid and 1 micromol/L ryanodine (n=8). Pyruvate significantly increased intracellular pH from 7.31+/-0.03 to 7.40+/-0.04 by BCECF fluorescence (n=6). CONCLUSIONS: The present findings indicate that pyruvate improves contractile performance of failing human myocardium by increasing intracellular Ca(2+) transients as well as myofilament Ca(2+) sensitivity. The former seem to result from increased SR Ca(2+) accumulation and release, the latter from increased intracellular pH.

Aequorin↗

PubMedDate not supplied

Pyruvate-induced long-term maintenance of glutathione s-transferase in rat hepatocyte cultures.

The addition of pyruvate to the culture medium has been reported to improve the maintenance of P450-dependent enzyme expression in primary rat hepatocyte cultures. In this study, the effects of 30mM pyruvate on cell morphology, albumin secretion and glutathione S-transferase (GST) expression were investigated as a function of the time in culture. The effect of triiodothyronine (T3) exposure on GST expression was also measured in pyruvate-treated cultures. Transmission electron microscopy showed that untreated hepatocytes deteriorated after culture for 7 days, whereas the morphology of the pyruvate-treated cells was similar to that observed in intact liver tissue. The albumin secretion rate was significantly higher in rat hepatocytes exposed to pyruvate than in control cells. In the presence of pyruvate, mu and alpha class GST activities were well maintained, whereas GST pi activity was increased over the entire culture period. HPLC analysis revealed that the complement of GST subunits present in hepatocytes is altered during culture with pyruvate: mu,class proteins remained relatively constant, whereas a decrease in the alpha class content was accompanied by a strong increase in GST subunit P1 (GSTP1). The induction of GSTP1 was confirmed at the mRNA level. In control cultures, pi class GST activity was increased, but total, mu, and alpha class GST activities continuously declined as a function of culture time and became undetectable beyond 7 days in culture. At the protein and mRNA levels, a much smaller increase in GSTP1 was observed than in the pyruvate cultures. When the pyruvate-treated cell cultures were exposed to T3, an inhibitory effect on GST activities and proteins was found. These results indicate that this simple culture model could be useful for studying the expression and regulation of GST.

Albumins↗

PubMed1982

Enzymologic studies and therapy of Leigh's disease associated with pyruvate decarboxylase deficiency.

An 11-month-old boy with muscle hypotonia and neurologic deteriorations had lactic acidosis, pyruvic acidemia and alaninemia due to deficiency of the pyruvate dehydrogenase complex in his platelets and of pyruvate decarboxylase in his muscle. When placed on a low carbohydrate-high fat diet for 6 months, his blood levels of lactate and pyruvate became nearly normal, but his cerebrospinal fluid levels of lactate and pyruvate remained high. Despite this dietary therapy, neurologic deterioration progressed slowly. He died of pneumonia after artificial respiration for 3 wk. At autopsy, extensive symmetric lesions were found in the brain including proliferation of capillaries and gliosis in the brain stem and diffuse demyelination in the white matter. These lesions were consistent with those observed in Leigh's disease. The activities of the pyruvate dehydrogenase complex and pyruvate decarboxylase in various tissues obtained at autopsy were less than 10% of control values; however, the activities of pyruvate carboxylase and alpha-ketoglutarate decarboxylase were within the normal limits. This patient with Leigh's disease had an isolated deficiency of pyruvate decarboxylase in various tissues.

Blood Platelets↗

PubMed2000

Intact smooth muscle metabolism: its responses to cyanide poisoning and pyruvate stimulation.

Smooth muscle mitochondria are unique in their compartmentalization of metabolism with the contractile proteins and putative role in cell fate choice. In this study we examine the relative and quantitative differences that smooth muscle mitochondria have with regard to cyanide inhibition. The effect of cyanide poisoning in the mitochondria of smooth muscle was examined in the intact porcine carotid artery and intact guinea pig stomach. The respiratory responses of these tissues were monitored in the presence of cyanide and following the addition of various metabolites. In HEPES buffer with 10 mM glucose as the substrate, it was found that the EC50 for cyanide inhibition was 0.11+/-0.02 and 0.14+/-0.02 mM in the pig carotid and guinea stomach respectively. We also found that the signaling metabolite, pyruvate could partially reverse this inhibition. With pyruvate (10 mM) as the substrate, the EC50 increased significantly to 6.52+/-0.11 (carotid artery) and 1.95+/-0. 30 (stomach) mM as well as being significantly different between the tissues. This apparent resistance to cyanide inhibition caused by pyruvate was lost when sodium bicarbonate buffer was used (EC50 in the presence of pyruvate of 0.13+/-0.04 and 0.25+/-0.04 for carotid and stomach respectively). HEPES buffer permitted pyruvate's protection from cyanide poisoning whereas bicarbonate buffer did not. The rate of respiration caused by pyruvate re-stimulation was not significantly different than control in the stomach (2.63+/-0.77 and 2.69+/-0.3??Mol O2/min/g dw respectively) but was significantly greater in the carotid artery. Therefore, smooth muscle with 10 mM pyruvate and 1 mM cyanide had a rate or respiration significantly greater than with 10 mM glucose alone (0.90+/-0.2 and 0.59+/-0. 06??Mol O2/min/g dw respectively). Using 31P NMR spectroscopy, we observed a complete normalisation of high energy phosphates and pH in the guinea pig stomach smooth muscle caused by pyruvate after cyanide poisoning. These results suggest that cyanide's toxicity of smooth muscle oxidative metabolism is affected by the buffer (HEPES versus Bicarbonate) and metabolic signalling molecules or substrates (pyruvate versus glucose) in which the tissues are exposed to as well as tissue to tissue variations.

Animals↗

PubMed2000

A pyruvate-proton symport and an H+-ATPase regulate the intracellular pH of Trypanosoma brucei at different stages of its life cycle.

Regulation of intracellular pH (pH(i)) and H(+) efflux were investigated in Trypanosoma brucei bloodstream and procyclic trypomastigotes using the fluorescent dyes 2', 7'-bis-(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF) acetoxymethyl ester and free BCECF respectively. pH(i) in bloodstream and procyclic trypomastigotes was 7.47+/-0.06 and 7. 53+/-0.07 respectively. Differences in the mechanisms for the regulation of pH(i) were noted between bloodstream and procyclic forms. Procyclic trypomastigotes maintained their pH(i) at neutral over a wide range of external pH values from 6 to 8, and in the absence of K(+) or Na(+). The H(+)-ATPase inhibitors N, N'-dicyclohexylcarbodi-imide (DCCD), diethylstilboestrol and N-ethylmaleimide substantially decreased the steady-state pH(i) and inhibited its recovery from acidification. The rate of H(+) efflux in these forms was determined to be 62+/-6.5 nmol/min per mg of protein, and was substantially decreased by H(+)-ATPase inhibitors. The data support the presence of an H(+)-ATPase as the major regulator of pH(i) in procyclic trypomastigotes. In contrast, bloodstream trypomastigotes were unable to maintain a neutral pH under acidic conditions, and their steady-state pH(i) and recovery from acidification were unaffected by H(+)-ATPase inhibitors, except for DCCD (100 microM). Their steady-state pH(i) was markedly decreased in glucose-free buffer or by >/=10 mM pyruvate, whereas procyclic trypomastigotes were unaffected by similar treatments. The rate of H(+) efflux in bloodstream trypomastigotes was 534+/-38 nmol/min per mg of protein, and was decreased in the absence of glucose and by the addition of pyruvate or DCCD. Pyruvate efflux in these forms was calculated to be 499+/-34 nmol/min per mg of protein, and was significantly inhibited by DCCD, 4, 4'-di-isothiocyanatodihydrostilbene-2,2'-disulphonic acid and alpha-cyanohydroxycinnamic acid. The pyruvate analogues beta-hydroxypyruvate, 3-bromopyruvate, 3-oxoglutarate, oxaloacetate, 3-oxoisovalerate and 3-oxoisohexanoate significantly decreased pH(i), as well as proton and pyruvate efflux, whereas lactate had only a small effect, and no effect was observed with citrate or fumarate. The inhibition by pyruvate analogues of pyruvate efflux, proton efflux and acidification of pH(i) supports the hypothesis that pyruvate efflux is accompanied by proton efflux and that this is the major pH(i) control mechanism in bloodstream forms. Inhibition by H(+)-ATPase inhibitors of residual H(+) efflux in the absence of glucose or in the presence of high extracellular pyruvate indicates a minor role for H(+)-ATPase(s) in control of pH(i) in bloodstream forms.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

PubMed1976

Studies on the mechanism and stereochemical properties of the oxalacetate decarboxylase activity of pyruvate kinase.

When cod fish muscle oxalacetate decarboxylase catalyzes the decarboxylation of oxalacetate in the presence of NaBH4, L-lactate results from the reduction of enzyme-bound pyruvate. However, D-lactate results when borohydride reduces the binary enzyme-pyruvate complex formed by adding pyruvate from solution, as reported by others. This observation suggests that there are alternate mechanisms for reduction that are either kinetically or sterically determined for the E-pyruvate forms produced in the two directions. In the process of investigating the mechanism of reduction, the cod fish muscle decarboxylase was discovered to be identical with pyruvate kinase. Decarboxylase activity appears to take place at a site which overlaps the phosphoenolpyruvate binding site on this enzyme, as discussed in the following paper. Crystalline rabbit muscle pyruvate kinase also contains significant decarboxylase activity indicating that the two reactions may be structurally related functions. In the presence of K+, orthophosphate, or ATP the rabbit muscle enzyme catalyzes the detritiation of enzyme-bound pyruvate formed during decarboxylation before release of pyruvate from the enzyme, in analogy with the detritiation of pyruvate formed from P-[3-3/]enolpyruvate in the kinase reaction. This observation is consistent with the formation of an enolpyruvate intermediate common to the kinetic pathways of both reactions. Since the decarboxylase reac.tion is completely stereospecific, within the limits of detection, going with retention of configuration, the protonation of the enolpyruvate intermediate is completely determined by the enzyme as is the case with the enolpyruvate intermediate generated from P-enolpyruvate in the kinase reaction.

Animals↗

PubMed1976

Chromium(III)-adenosine triphosphate as a paramagnetic probe to determine intersubstrate distances on pyruvate kinase. Detection of an active enzyme-metal-ATP-metal complex.

The interaction of CrATP, a stable, substitution-inert, paramagnetic tridentate complex of ATP, with muscle pyruvate kinase has been studied by measuring the effects of CrATP on the kinetics of pyruvate enolization and on the longitudinal nuclear magnetic relaxation rate (1/T1) of the protons of water and the protons and carbon atoms of pyruvate to investigate the existence and activity of bimetallic enzyme-M(II)-CrATP complexes and to determine intersubstrate distances on a kinase. The paramagnetic effect of CrATP on 1/T1 of water protons is enhanced upon complexation with the enzyme. Titrations of the enzyme with CrATP yielded characteristic enhancements of 1/T1 for the binary enzyme-CrATP, ternary enzyme-Mg(II)-crATP, and quaternary enzyme-Mg(II)-crATP-pyruvate complexes of 3.5, 1.7, and 1.2 and dissociation constants of CrATP of 400, 200, and 200 muM, respectively. From the frequency dependence of 1/T1, the number of fast exchanging water protons in the coordination spheres of Cr(III) is approximately 6 in CrATP and in both the ternary enzyme-Mg(II)-CrATP complex and the quaternary enzyme-Mg(II)-CrATP-pyruvate complex. The paramagnetic effect of enzyme-bound Mn(II) on 1/T1 of water protons decreases upon the addition of CrATP. Titration of the binary enzyme-Mn(II) complex with CrATP decreases the characteristic enhancement due to Mn(II) from 24 +/- 3 to 6 +/- 1. Titration of the ternary eznyme-Mn(II)-pyruvate complex with CrATP decreases the enhancement from 6 +/- 1 to 0.5 +/- 0.1. The affinity of the enzyme for Mn(II) is increased 2-fold upon binding of CrATP as indicated by decreases in the amplitude of the EPR spectrum of free Mn(II). The dissociation constants of CrATP from the enzyme-Mn(II)-CrATP complex, the enzyme-CrATP-pyruvate complex, and the enzyme-Mn(II)-CrATP-pyruvate complex are all 200 muM. The observed titration behavior, the characteristic enhancement values, the tightening by Mg(II) of the binding of CrATP to the enzyme, and the tightening of the binding of Mn(II) to the enzyme by CrATP establish the existence of enzyme-M(II)-CrATP and enzyme-M(II)-CrATP-pyruvate complexes containing two cations, Mg(II) or Mn(II) and Cr(III), at the active site.

Adenosine Triphosphate↗

PubMedDate not supplied

[Pyruvate metabolism in rats with dietary B1 avitaminosis].

The influence of alimentary deficiency of thiamine on the pyruvate metabolism in the liver and blood of rats was investigated. Note is taken of a fallen activity of pyruvate-dehydrogenase (PDH) and a rising level of pyruvate in the blood and liver. An inverse relationship between the PDH activity and the pyruvate content in the liver, observed during the whole course of the experiment is in evidence, although the substrate level exceeds significantly that of the control only starting from the 20th day. In the normalization of the pyruvate level in the liver all the studied enzymatic systems partake; they join stagewise in the order of alanine-aminotransferase, pyruvate-kinase, malate-enzyme, which differently change their activity in the course of the experiment, along with physiological mechanisms of the pyruvate transport into the blood. These are most pronounced starting from the 20th day (inverse relationships of the pyruvate levels in the blood and liver). During the whole of the experiment a direct relation between the lactate content in the blood and liver persists. In these tissues no relation between the pyruvate and lactate levels was revealed.

Animals↗

PubMed1997

[Erythrocyte pyruvate kinase--an enzyme that may have an influence on oxygen transport to tissues].

Hemoglobin, the critical protein in the delivery of oxygen to mammalian tissues, is poorly adapted to that function. This awkward situation is remedied by the presence in the red cell of 5 to 7 mM 2.3 DPG, which binds to Hb competitively with oxygen and reduces oxygen affinity. How the levels of 2.3 DPG in the red cell are regulated is an important question that has not yet been fully answered. The best established correlation with 2.3 DPG concentration in red cells is the activity of the enzyme pyruvate kinase. Inverse relationship between 2.3 DPG content and pyruvate kinase activity is the result of two conditions within the erythrocyte. The metabolites between FBP and PEP are in a state of quasi equilibrium because the activity of pyruvate kinase is so much lower than the activities of other enzymes in the pathway. Furthermore, pyruvate kinase operates, in vivo at a PEP concentration well below the Km concentration. In consequence, an increase in the glycolytic rate or inhibition of pyruvate kinase causes an increase in PEP concentration. Increases in PEP levels lead to increases in the levels of 2.3 DPG, and hence to increase in the level of 2.3 DPG via the 2.3 DPG synthase reaction. This relationship is demonstrated by the frequent occurrence of elevated levels of 2.3 DPG in pyruvate kinase deficient erythrocytes and by the decreased levels of 2.3 DPG and PEP which are observed in erythrocytes containing a pyruvate kinase with abnormally high activity at low PEP levels. It is thus clear that control of pyruvate kinase activity is a means to the control of oxygen delivery by the erythrocyte. It remains to be discovered whether any of the observed variations in human PK activity are due to reversible posttranslational modification and whether the potential for control of oxygen delivery via changes in pyruvate kinase activity is made use of the normal human adult. The availability of human full length of cDNA for PK should accelerate our understanding of he structure-function relationships of PK deficiency and enhance the possibility of gene therapy for seriously affected PK patients.

Adult↗

PubMed1997

Pyruvate protects neurons against hydrogen peroxide-induced toxicity.

Hydrogen peroxide (H2O2) is suspected to be involved in numerous brain pathologies such as neurodegenerative diseases or in acute injury such as ischemia or trauma. In this study, we examined the ability of pyruvate to improve the survival of cultured striatal neurons exposed for 30 min to H2O2, as estimated 24 hr later by the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazoliumbromide assay. Pyruvate strongly protected neurons against both H2O2 added to the external medium and H2O2 endogenously produced through the redox cycling of the experimental quinone menadione. The neuroprotective effect of pyruvate appeared to result rather from the ability of alpha-ketoacids to undergo nonenzymatic decarboxylation in the presence of H2O2 than from an improvement of energy metabolism. Indeed, several other alpha-ketoacids, including alpha-ketobutyrate, which is not an energy substrate, reproduced the neuroprotective effect of pyruvate. In contrast, lactate, a neuronal energy substrate, did not protect neurons from H2O2. Optimal neuroprotection was achieved with relatively low concentrations of pyruvate (</=1 mM), whereas at high concentration (10 mM) pyruvate was ineffective. This paradox could result from the cytosolic acidification induced by the cotransport of pyruvate and protons into neurons. Indeed, cytosolic acidification both enhanced the H2O2-induced neurotoxicity and decreased the rate of pyruvate decarboxylation by H2O2. Together, these results indicate that pyruvate efficiently protects neurons against both exogenous and endogenous H2O2. Its low toxicity and its capacity to cross the blood-brain barrier open a new therapeutic perspective in brain pathologies in which H2O2 is involved.

Animals↗