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Effect of alpha-ketobutyrate on palmitic acid and pyruvate metabolism in isolated rat hepatocytes.

alpha-Ketobutyrate, an intermediate in the catabolism of threonine and methionine, is metabolized to CO2 and propionyl-CoA. Recent studies have suggested that propionyl-CoA may interfere with normal hepatic oxidative metabolism. Based on these observations, the present study examined the effect of alpha-ketobutyrate on palmitic acid and pyruvate metabolism in hepatocytes isolated from fed rats. alpha-Ketobutyrate (10 mM) inhibited the oxidation of palmitic acid by 34%. In the presence of 10 mM carnitine, the inhibition of palmitic acid oxidation by alpha-ketobutyrate was reduced to 21%. These observations are similar to those previously reported using propionate as an inhibitor of fatty acid oxidation, suggesting that propionyl-CoA may be responsible for the inhibition. alpha-Ketobutyrate (10 mM) inhibited 14CO2 generation from [14C]pyruvate by more than 75%. This inhibition was quantitatively larger than seen with equal concentrations of propionate. Carnitine (10 mM) had no effect on the inhibition of pyruvate oxidation by alpha-ketobutyrate despite the generation of large amounts of propionylcarnitine during the incubation. alpha-Ketobutyrate inhibited [14C]glucose formation from [14C]pyruvate by more than 60%. This contrasted to a 30% inhibition caused by propionate. These results suggest that alpha-ketobutyrate inhibits hepatic pyruvate metabolism by a mechanism independent of propionyl-CoA formation. The present study demonstrates that tissue accumulation of alpha-ketobutyrate may lead to disruption of normal cellular metabolism. Additionally, the production of propionyl-CoA from alpha-ketobutyrate is associated with increased generation of propionylcarnitine. These observations provide further evidence that organic acid accumulation associated with a number of disease states may result in interference with normal hepatic metabolism and increased carnitine requirements.

Acyl Coenzyme A↗

Vasopressin stimulates pyruvate utilization through a Ca(2+)-dependent mechanism and lactate formation by a protein kinase C-dependent mechanism in isolated rat hepatocytes.

Vasopressin stimulates lactate production by hepatocytes from fed rats, an effect which has been attributed exclusively to Ca2+ activation of glycogenolysis. We provide evidence here for two further actions of vasopressin which affect lactate formation by rat hepatocytes. In the presence of 50 mM glucose, vasopressin inhibited lactate production by hepatocytes. The inhibition was relieved by the presence of alpha-cyano-4-hydroxycinnamate (alpha-CHC), which blocks mitochondrial pyruvate transport. This suggests that vasopressin stimulates pyruvate utilization in the presence of a high concentration of glucose. Epidermal growth factor (EGF), which also increases lactate formation by hepatocytes, did not similarly decrease lactate accumulation in the presence of high glucose, suggesting no stimulation of lactate and pyruvate utilization by this hormone. In cells depleted of Ca2+, vasopressin also stimulated lactate formation. Although vasopressin did not cause the apparent translocation of protein kinase C between cell spaces, phospholipase C treatment of hepatocytes did duplicate vasopressin stimulation of lactate formation, provided fatty acid oxidation was suppressed by the simultaneous presence of the inhibitor palmixorate. We conclude that three actions of vasopressin affect lactate and pyruvate formation: the calcium-linked activations of glycogenolysis and mitochondrial pyruvate utilization, and a stimulation of glycolysis likely mediated by protein kinase C.

Adenosine Triphosphate↗

Stimulatory effect of ADP, ATP, NAD(P) on pyruvate production from malate by uncoupled human placental mitochondria.

It has been shown that ADP, ATP, NAD(P), and NAD(P)H significantly stimulate pyruvate production from malate by intact uncoupled human term placental mitochondria. No stimulation by ADP was observed when mitochondria were incubated in the presence of NAD(P) or NAD(P)H or when mitochondrial membrane had been disrupted. Atractyloside and oligomycin were without effect on ADP- and ATP-stimulated pyruvate production. Other dinucleotides tested such as GDP, UDP, and CDP, stimulated pyruvate production only slightly when mitochondria were incubated in the absence of phosphate. The rate of pyruvate production by intact mitochondria is commensurate with partly purified NAD(P)-linked malic enzyme activity as measured by NAD(P) reduction as far as the effects of pH of hydroxymalonate on these both processes is concerned. It is concluded that pyruvate production by intact human placental mitochondria is catalyzed by NAD(P)-linked malic enzyme and that this process is stimulated by ADP and ATP.

Adenosine Diphosphate↗

Pyruvate carboxylase deficiency: acute exacerbation after ACTH treatment of infantile spasms.

Pyruvate carboxylase deficiency results in congenital lactic acidosis. We report the significant finding in a child with infantile spasms controlled with adrenocorticotrophin hormone (ACTH) but who then developed severe lactic acidosis; pyruvate carboxylase deficiency was subsequently diagnosed. Blood lactate, pyruvate, and alanine levels were elevated, as well as cerebrospinal fluid alanine. Plasma alanine concentration was doubled by ACTH therapy. Fibroblasts contained extremely low pyruvate carboxylase activity. The patient died at 12 weeks of age after recurrent episodes of profound acidosis. At autopsy, the brain manifested cystic degeneration and demyelination. Pyruvate carboxylase deficiency is associated with neonatal onset of acidosis, delayed development, seizures, hypotonia, recurrent profound acidosis, and early death. The dramatic rise in plasma alanine content coincident with ACTH therapy suggest that ACTH played a role in precipitating the catastrophic metabolic acidosis.

Acidosis, Lactic↗

Is pyruvate an endogenous anti-inflammatory molecule?

Pyruvic acid is an effective scavenger of reactive oxygen species. Ethyl pyruvate has demonstrated anti-inflammatory actions and improved hyperpermeability and bacterial translocation due to endotoxemia and is of benefit in animal models of sepsis and septic shock. Ethyl pyruvate specifically inhibits tumor necrosis factor-alpha production and decreases circulating levels of high-mobility group box-1 and nuclear factor-kappaB signaling pathways by specifically targeting its p65 subunit in animals with established endotoxemia or sepsis and in macrophage cultures. Ethyl pyruvate also decreases cyclo-oxygenase-2, inducible nitric oxide synthase, and interleukin-6 mRNA expression in the liver, ileal mucosa, and colonic mucosa in animal models with hemorrhagic shock. Similar beneficial actions have been seen in endotoxemia. These and other studies suggest that ethyl pyruvate could be of significant benefit in the treatment of patients who are critically ill and have sepsis/septic shock.

Animals↗

Pyruvate prevents ischemia-reperfusion mucosal injury of rat small intestine.

BACKGROUND: Since reactive oxygen intermediates (ROI, or free radicals) have been implicated in the pathogenesis of ischemia-reperfusion injury of the small bowel, we evaluated the pretreatment effect of pyruvate, a 3-carbon compound recently shown to inhibit superoxide production, on reperfusion mucosal injury in the rat. METHODS: The small bowel of the ACI rat (n = 6) was divided into 2 5-cm segments, and 10 mL of a liquid diet containing pyruvate (0.32 g) or placebo (0.26 g) was instilled into the lumen of one of the segments for 10 minutes. The bowel was then made completely ischemic for 45 minutes by clamping the superior mesenteric artery, which was followed by 60 minutes of reperfusion. RESULTS: The production of ROI in bowel biopsy samples, estimated by luminol-enhanced chemiluminescence, was at least 80% decreased in the segment containing pyruvate compared with placebo immediately after ischemia (time 0), and compared with 30 and 60 minutes of reperfusion (P < 0.05 for each time point). After 60 minutes of reperfusion, the bowel segment containing the placebo diet showed villus sloughing with destruction of lamina propria and crypts, and mucosal neutrophil infiltration had increased by 80%. Electron microscope evaluation revealed a reduction in number and size of microvilli, dilatation of intercellular spaces, and intracellular vacuoles. The bowel segment containing pyruvate showed the villi and crypts to be intact, without enhanced neutrophil infiltration. CONCLUSION: Pyruvate pretreatment of the rat small bowel inhibits postischemic reperfusion mucosal histologic injury, neutrophil infiltration, and ROI production.

Animals↗

Effects of aging on the activities of pyruvate dehydrogenase complex and its kinase in rat heart.

Effects of aging on the activities of heart pyruvate dehydrogenase complex and pyruvate dehydrogenase kinase were examined using 7, 35 and 60 wk old rats. Aging did not affect the total activity of pyruvate dehydrogenase complex but decreased the activity state (percentage of active form) of the complex in rats under the fed condition (52%, 36% and 26% for 7, 35 and 60 wk old rats, respectively). This decrease in the complex activity with aging was suggested to be associated with an age-related decrease in the blood glucose disposal. Starvation for 24 h decreased the activity state to less than 3% in all of the age groups. The activity of pyruvate dehydrogenase kinase associated with the complex was not related to the alteration in the activity state of the complex; the kinase activity was slightly lower in 60 wk old rats than in the younger rats under the fed condition and activation of the kinase by starvation was greater in the younger rats. The mechanism for the decrease in activity of pyruvate dehydrogenase complex was discussed on the basis of glucose and fatty acid utilization of heart muscle cells.

Aging↗

Glycolysis and pyruvate oxidation in cardiac hypertrophy--why so unbalanced?

Cardiac hypertrophy, induced by chronic pressure or volume overload, is associated with abnormalities in energy metabolism as well as characteristic increases in muscle mass and alterations in the structure of the heart. Hypertrophied hearts display increased rates of glycolysis and overall glucose utilization, but rates of pyruvate oxidation do not rise in step with rates of pyruvate generation. Glycolysis and glucose oxidation, therefore, become markedly less 'coupled' in hypertrophied hearts than in non-hypertrophied hearts. Because the pyruvate dehydrogenase complex (PDC) contributes so powerfully to the control of glucose oxidation, we set out to test the hypothesis that the function of PDC is impaired in cardiac hypertrophy. In this review we describe evidence indicating that the alterations in glucose metabolism in hypertrophied hearts cannot be explained simply by changes in PDC expression or control. Additional mechanisms that may lead to an altered balance of pyruvate metabolism in cardiac hypertrophy are discussed, with commentaries on possible changes in pyruvate transport, NADH shuttles, lactate dehydrogenase, and amino acid metabolism.

Animals↗

Role of lysine 240 in the mechanism of yeast pyruvate kinase catalysis.

Site-directed mutagenesis was used to change Lys 240 of yeast pyruvate kinase (Lys 269 in muscle PK) to Met. K240M has an absolute requirement for FBP for catalysis. K240M is 100- and 1000-fold less active than wild-type YPK in the presence of Mn(2+) and Mg(2+), respectively. Steady-state fluorescence titration data suggest that the substrate PEP binds to K240M with the same affinity as it does to wild-type YPK. The rate of phosphoryl transfer in K240M has been decreased >1000-fold compared to wild-type YPK. The detritiation of 3-[(3)H]pyruvate catalyzed by YPK occurs at a rate significantly greater than the spontaneous rate. Detritiation of pyruvate by wild-type YPK occurs as a divalent metal- and FBP-dependent process requiring ATP. There is no detectable detritiation of pyruvate catalyzed by K240M. The solvent deuterium isotope effect on k(cat) is 2.7 +/- 0.2 and 1.6 +/- 0.1 for the wild type and for K240M YPK, respectively. This suggests that the isotope sensitive step in the PK reaction does not involve Lys 240 and that the enolpyruvate intermediate is still protonated by K240M. Isotope trapping was used to characterize enolpyruvate protonation by K240M. While there was enrichment of the methyl protons of pyruvate from labeled solvent formed by catalysis with muscle PK and wild-type YPK, only background levels of tritium were trapped with K240M. In K240M, the proton donor exchanges protons with the solvent at a higher rate relative to turnover than does the proton donor in wild-type YPK. The pH-rate profile of K240M exhibits the loss of a pK(a) value of 8. 8 observed with wild-type YPK. The above data and recent crystal structure data suggest that Lys 240 interacts with the phosphoryl group of phosphoenolpyruvate and helps to stabilize the pentavalent phosphate transition state during phosphoryl transfer. Phosphoryl transfer is highly coupled to proton transfer, or Lys 240 also affects enolate protonation.

Catalysis↗

Increased pyruvate efficiency in enzymatic production of (R)-phenylacetylcarbinol.

Loss of substrate, pyruvate, a limitation for enzymatic batch production of (R)-phenylacetylcarbinol (PAC), resulted from two phenomena: temperature dependent non-enzymatic concentration decrease due to the cofactor Mg2+ and formation of by-products, acetaldehyde and acetoin, by pyruvate decarboxylase (PDC). In the absence of enzyme, pyruvate stabilization was achieved by lowering the Mg2+ concentration from 20 to 0.5 mM. With 0.5 mM Mg2+ Rhizopusjavanicus and Candida utilis PDC produced similar levels of PAC (49 and 51 g 1(-1), respectively) in 21 h at 6 degrees C; however C. utilis PDC formed less by-product from pyruvate and was more stable during biotransformation. The process enhancements regarding Mg2+ concentration and source of PDC resulted in an increase of molar yield (PAC/consumed pyruvate) from 59% (R. javanicus PDC, 20 mM Mg2+) to 74% (R. javanicus PDC, 0.5 mM Mg2+) to 89% (C. utilis PDC, 0.5 mM Mg2+).

Acetaldehyde↗

Factors afecting the activity of pyruvate kinase of Acetobacter xylinum.

1. Extracts of Acetobacter xylinum were found to contain the glycolytic enzymes involved in the conversion of triose phosphate into pyruvate. Pyruvate kinase had the lowest relative activity. Phosphofructokinase activity was not detected in the extracts. 2. Only slight differences in the activity of pyruvate kinase were observed between cells grown on glucose and those grown on intermediates of the tricarboxylic acid cycle. 3. Pyruvate kinase, partially purified from ultrasonic extracts by ammonium sulphate fractionation, required Mg(2+) ions for activity. It was not activated by K(+) or NH(4) (+) ions. 4. The plots representing the relationship between initial velocity and phosphoenolpyruvate concentration were sigmoidal, suggesting a co-operative effect for phosphoenolpyruvate. The Hill coefficient (n) for phosphoenolpyruvate was 2. The rate of the reaction changed with increasing ADP concentrations according to normal Michaelis-Menten kinetics. 5. The enzyme was inhibited by ATP (K(i)0.9x10(-3)m). The inhibition was competitive with regard to ADP but not with regard to phosphoenolpyruvate. It was not relieved by excess of Mg(2+) ions. 6. The possible relationship of the properties of pyruvate kinase to regulatory mechanisms for controlling gluconeogenesis and carbohydrate oxidation in A. xylinum is discussed.

Adenine Nucleotides↗

Pig liver pyruvate carboxylase. The reaction pathway for the decarboxylation of oxaloacetate.

1. The reaction pathway for the decarboxylation of oxaloacetate, catalysed by pig liver pyruvate carboxylase, was studied in the presence of saturating concentrations of K(+) and acetyl-CoA. 2. Free Mg(2+) binds to the enzyme in an equilibrium fashion and remains bound during all further catalytic cycles. MgADP(-) and P(i) bind randomly, at equilibrium, followed by the binding of oxaloacetate. Pyruvate is released before the ordered steay-state release of HCO(3) (-) and MgATP(2-). 3. These results are entirely consistent with studies on the carboxylation of pyruvate presented in the preceding paper (Warren & Tipton, 1974b) and together they allow a quantitative description of the reaction mechanism of pig liver pyruvate carboxylase. 4. In the absence of other substrates of the back reaction pig liver pyruvate carboxylase will decarboxylate oxaloacetate in a manner that is not inhibited by avidin. 5. Reciprocal plots involving oxaloacetate are non-linear curves, which suggest a negatively co-operative interaction between this substrate and the enzyme.

Acetyl Coenzyme A↗

Kinetic properties of rat liver pyruvate kinase at cellular concentrations of enzyme, substrates and modifiers.

Kinetic properties of rat liver pyruvate kinase type I at pH7.5 and 6.5 were studied with physiological ranges of substrates, modifiers and Mg(2+) concentrations at increasing enzyme concentrations, including the estimated cellular concentrations (approx. 0.1mg/ml). Enzyme properties appear unaffected by increased enzyme concentration if phosphoenolpyruvate, fructose 1,6-diphosphate and inhibitors are incubated with enzyme before starting the reaction with ADP. Our data suggest that minimum cellular concentrations of MgATP and l-alanine provide virtually complete inhibition of pyruvate kinase I at pH7.5. The most likely cellular control of existing pyruvate kinase I results from the strong restoration of enzyme activity by the small physiological amounts of fructose 1,6-diphosphate. Decreasing the pH to 6.5 also restores pyruvate kinase activity, but to only about one-third of its activity in the presence of fructose 1,6-diphosphate. Neither pyruvate nor 2-phosphoglycerate at cellular concentrations inhibit the enzyme significantly.

Adenosine Diphosphate↗

Role of pyruvate dehydrogenase kinase isoenzyme 4 (PDHK4) in glucose homoeostasis during starvation.

The PDC (pyruvate dehydrogenase complex) is strongly inhibited by phosphorylation during starvation to conserve substrates for gluconeogenesis. The role of PDHK4 (pyruvate dehydrogenase kinase isoenzyme 4) in regulation of PDC by this mechanism was investigated with PDHK4-/- mice (homozygous PDHK4 knockout mice). Starvation lowers blood glucose more in mice lacking PDHK4 than in wild-type mice. The activity state of PDC (percentage dephosphorylated and active) is greater in kidney, gastrocnemius muscle, diaphragm and heart but not in the liver of starved PDHK4-/- mice. Intermediates of the gluconeogenic pathway are lower in concentration in the liver of starved PDHK4-/- mice, consistent with a lower rate of gluconeogenesis due to a substrate supply limitation. The concentration of gluconeogenic substrates is lower in the blood of starved PDHK4-/- mice, consistent with reduced formation in peripheral tissues. Isolated diaphragms from starved PDHK4-/- mice accumulate less lactate and pyruvate because of a faster rate of pyruvate oxidation and a reduced rate of glycolysis. BCAAs (branched chain amino acids) are higher in the blood in starved PDHK4-/- mice, consistent with lower blood alanine levels and the importance of BCAAs as a source of amino groups for alanine formation. Non-esterified fatty acids are also elevated more in the blood of starved PDHK4-/- mice, consistent with lower rates of fatty acid oxidation due to increased rates of glucose and pyruvate oxidation due to greater PDC activity. Up-regulation of PDHK4 in tissues other than the liver is clearly important during starvation for regulation of PDC activity and glucose homoeostasis.

Animals↗

Ammonium chloride inhibits pyruvate oxidation in rat liver mitochondria: a possible cause of fatty liver in Reye's syndrome and urea cycle defects.

1. Earlier studies with liver slices showed that inhibition by NH4+ of the oxidation of palmitate to CO2 was greater than total oxidation, whereas salicylate exerted a stronger inhibitory effect on the latter. We have now investigated the effects of NH4Cl and salicylate on ADP-induced O2 consumption by mitochondria (State 3 rate) respiring on pyruvate, and oxidation of [1-14C]- and [2-14C]-pyruvate to 14CO2. 2. The rate of State 3 respiration was inhibited and plateaued at 45% with 10 mmol/l NH4Cl. 3. Oxidation of [1-14C]pyruvate was not significantly affected by either NH4Cl or salicylate. Oxidation of [2-14C]pyruvate was strongly inhibited and plateaued at 70% with 1 mmol/l NH4Cl (IC50 = 0.125 mmol/l). ADP (1 mmol/l) increased the rate of decarboxylation of [2-14C]pyruvate but the extent of NH4Cl inhibition was not affected. Salicylate had a slight activating effect in the absence or presence of NH4Cl. 4. These results indicate that NH4Cl inhibits the oxidative metabolism of acetyl-CoA in the tricarboxylic acid cycle. Therefore, inhibition of fatty acid oxidation to acetyl-CoA as well as its further oxidative metabolism occurring under hyperammonaemia (> 0.1 mmol-1.49 mmol/l in Reye's syndrome patients) may be one of the causes of fatty acidaemia. 5. The cumulative inhibitory effects of NH4+ and fatty acyl derivatives on mitochondrial oxidative metabolism and production of ATP, as well as the uncoupling effects of salicylate, may contribute to some of the pathophysiology observed in patients with Reye's syndrome, and enzyme defects of the urea cycle.

Adenosine Diphosphate↗

Pyruvate decarboxylase from Kluyveromyces lactis. An enzyme with an extraordinary substrate activation behaviour.

Pyruvate decarboxylase (EC 4.1.1.1) was isolated and purified from the yeast Kluyveromyces lactis. The properties of this enzyme relating to the native oligomeric state, the subunit size, the nucleotide sequence of the coding gene(s), the catalytic activity, and protein fluorescence as well as circular dichroism are very similar to those of the well characterized pyruvate decarboxylase species from yeast. Remarkable differences were found in the substrate activation behaviour of the two pyruvate decarboxylases using three independent methods: steady-state kinetics, stopped-flow measurements, and kinetic dilution experiments. The dependence of the observed activation rate constant on the substrate concentration of pyruvate decarboxylase from K. lactis showed a minimum at a pyruvate concentration of 1.5 mm. According to the mechanism of substrate activation suggested this local minimum occurs due to the big ratio of the dissociation constants for the binding of the first (regulatory) and the second (catalytic) substrate molecule. The microscopic rate constants of the substrate activation could be determined by a refined fit procedure. The influence of the artificial activator pyruvamide on the activation of the enzyme was studied.

Catalytic Domain↗

Pyruvate formate-lyase and a novel route of eukaryotic ATP synthesis in Chlamydomonas mitochondria.

Pyruvate formate-lyase (PFL) catalyzes the non-oxidative conversion of pyruvate to formate and acetyl-CoA. PFL and its activating enzyme (PFL-AE) are common among strict anaerobic and microaerophilic prokaryotes but are very rare among eukaryotes. In a proteome survey of isolated Chlamydomonas reinhardtii mitochondria, we found several PFL-specific peptides leading to the identification of cDNAs for PFL and PFL-AE, establishing the existence of a PFL system in this photosynthetic algae. Anaerobiosis and darkness led to increased PFL transcripts but had little effect on protein levels, as determined with antiserum raised against C. reinhardtii PFL. Protein blots revealed the occurrence of PFL in both chloroplast and mitochondria purified from aerobically grown cells. Mass spectrometry sequencing of C. reinhardtii mitochondrial proteins, furthermore, identified peptides for phosphotransacetylase and acetate kinase. The phosphotransacetylase-acetate kinase pathway is a common route of ATP synthesis or acetate assimilation among prokaryotes but is novel among eukaryotes. In addition to PFL and pyruvate dehydrogenase, the algae also expresses pyruvate:ferredoxin oxidoreductase and bifunctional aldehyde/alcohol dehydrogenase. Among eukaryotes, the oxygen producer C. reinhardtii has the broadest repertoire of pyruvate-, ethanol-, and acetate-metabolizing enzymes described to date, many of which were previously viewed as specific to anaerobic eukaryotic lineages.

Acetylesterase↗

Plasma lipid concentrations in hyperlipidemic patients consuming a high-fat diet supplemented with pyruvate for 6 wk.

We evaluated the effects of a three-carbon compound, pyruvate, on plasma lipid concentrations in hyperlipidemic patients consuming a high-cholesterol (560-620 mg), high-fat (45-47% of energy; 18-20% of energy as saturated fatty acid), anabolic diet (0.11-0.12 MJ/kg body wt) for 6 wk. Forty subjects consumed the diet, randomly supplemented with 36-53 g pyruvate (n = 19) or 21-37 g polyglucose (placebo, Polycose, n = 21) as a portion of carbohydrate energy. Plasma cholesterol and LDL-cholesterol concentrations were unchanged in the placebo group, but decreased by 4% and 5%, respectively, in the pyruvate group (P < 0.05 vs placebo). Plasma HDL-cholesterol, HDL3-cholesterol, and triglyceride concentrations were similar in both groups. Resting heart rate, diastolic blood pressure, and rate-pressure product were unchanged after 6 wk of therapy in the placebo group, but decreased by 9%, 6%, and 12%, respectively with pyruvate supplementation (P < 0.05 vs placebo). We conclude that pyruvate supplementation of a high-fat, high-cholesterol, anabolic diet will decrease plasma cholesterol and LDL-cholesterol concentrations without affecting the HDL-cholesterol concentration.

Blood Pressure↗