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PubMed1997

Pyruvate-extended amino acid derivatives as highly potent inhibitors of carboxyl-terminal peptide amidation.

Carboxyl-terminal amidation, a required post-translational modification for the bioactivation of many neuropeptides, entails sequential enzymatic action by peptidylglycine monooxygenase (PAM, EC 1.14.17.3) and peptidylamidoglycolate lyase (PGL, EC 4.3.2.5). The monooxygenase, PAM, first catalyzes conversion of a glycine-extended pro-peptide to the corresponding alpha-hydroxyglycine derivative, and the lyase, PGL, then catalyzes breakdown of this alpha-hydroxyglycine derivative to the amidated peptide plus glyoxylate. We now introduce the first potent inhibitors for peptidylamidoglycolate lyase. These inhibitors, which can be viewed as pyruvate-extended N-acetyl amino acids, constitute a novel class of compounds. They were designed to resemble likely transient species along the reaction pathway of PGL catalysis. A general synthetic procedure for preparation of pyruvate-extended N-acetyl amino acids or peptides is described. Since these compounds possess the 2,4-dioxo-carboxylate moiety, their solution tautomerization was investigated using both NMR and high performance liquid chromatography analyses. The results establish that freshly prepared solutions of N-Ac-Phe-pyruvate consist predominantly of the enol tautomer, which then slowly tautomerizes to the diketo form when left standing for several days in an aqueous medium; upon acidification, formation of the hydrate tautomer occurs. Kinetic experiments established that these novel compounds are highly potent, pure competitive inhibitors of PGL. Kinetic experiments with the ascorbate-dependent copper monooxygenases, PAM and dopamine-beta-monooxygenase, established that these compounds also bind competitively with respect to ascorbate; however, pyruvate-extended N-acyl-amino acid derivatives possessing hydrophobic side chains are much more potent inhibitors of PGL than of PAM. Selective targeting of N-Ac-Phe-pyruvate so as to inhibit the lyase, but not the monooxygenase, domain was demonstrated with the bifunctional amidating enzyme of Xenopus laevis. The availability of potent inhibitors of PGL should facilitate studies regarding the possible biological role of alpha-hydroxyglycine-extended peptides.

Amides↗

PubMed1998

Molecular analysis of two pyruvate dehydrogenase kinases from maize.

Two maize cDNAs were isolated and sequenced that had open reading frames with approximately 37% amino acid identity to mammalian pyruvate dehydrogenase kinases. Both maize kinase sequences contain the five domains with conserved signature residues typical of procaryotic two-component histidine kinases. Sequence comparisons identified six other highly conserved motifs that are proposed to be specific to pyruvate dehydrogenase kinases. In addition, specific Trp and Cys residues are also invariant in these sequences. The maize cDNAs are 1332 (PDK1) and 1602 (PDK2) nucleotides in length, encoding polypeptides with calculated molecular masses of 38,867 and 41,327 Da that share 77% amino acid identity. Reverse transcriptase-polymerase chain reaction analysis with oligonucleotide-specific primers revealed a differential expression pattern for the two isoforms. PDK1 and PDK2 were expressed in Escherichia coli with N-terminal His6 tags to facilitate purification. The recombinant proteins migrated at 44 and 48 kDa, respectively, during SDS-polyacrylamide gel electrophoresis. Anti-PDK1 antibodies immunoprecipitated 75% of pyruvate dehydrogenase kinase activity from a maize mitochondrial matrix fraction, and recognized a matrix protein of 43 kDa. Recombinant PDK2, expressed as a fusion with the maltose-binding protein, inactivated kinase-depleted maize pyruvate dehydrogenase complex when incubated with MgATP, coincident with incorporation of 32P from [gamma-32P]ATP into the alpha subunit of pyruvate dehydrogenase.

Amino Acid Sequence↗

PubMed2000

Exogenous Mg-ATP induces a large inhibition of pyruvate kinase in intact rat hepatocytes.

Mg-ATP infusion in vivo has been reported to be beneficial both to organ function and survival rate in various models of shock. Moreover, a large variety of metabolic effects has been shown to occur in several tissues due to purinergic receptor activation. In the present work we studied the effects of exogenous Mg-ATP in rat liver cells perifused with dihydroxyacetone to investigate simultaneously gluconeogenetic and glycolytic pathways. We found a significant effect on oxidative phosphorylation as characterized by a decrease in oxygen consumption rate and in the cellular ATP-to-ADP ratio associated with an increase in lactate-to-pyruvate ratio. In addition, exogenous Mg-ATP induced rapid and reversible inhibition of both gluconeogenesis and glycolysis. The main effect on gluconeogenesis was located at the level of the fructose cycle, whereas the decrease in glycolysis was due to a strong inhibition of pyruvate kinase. Although pyruvate kinase inhibition induced by exogenous Mg-ATP was allosteric when assessed in vitro after enzyme extraction, we found a large decrease in the apparent maximal velocity when kinetics were assessed in vivo in intact perifused hepatocytes. This newly described short-term regulation of pyruvate kinase occurs only in the intact cell and may open new potentials for the pharmacological regulation of pyruvate kinase in vivo.

Adenosine Diphosphate↗

PubMed2004

Kinetic mechanism and metabolic role of pyruvate phosphate dikinase from Entamoeba histolytica.

The kinetic mechanism and the metabolic role of pyruvate phosphate dikinase from Entamoeba histolytica were investigated. The initial velocity patterns in double reciprocal plots were parallel for the phosphoenolpyruvate/AMP and phosphoenolpyruvate/pyrophosphate substrate pairs and intersecting for the AMP/pyrophosphate pair. This suggests a kinetic mechanism with two independent reactions. The rate of ATP synthesis at saturating and equimolar concentrations of phosphoenolpyruvate, AMP, and pyrophosphate was inhibited by phosphate, which is consistent with an ordered steady-state mechanism. Enzyme phosphorylation by [(32)P(i)]pyrophosphate depends on the formation of a ternary complex between AMP, pyrophosphate, and pyruvate phosphate dikinase. In consequence, the reaction that involves the AMP/pyrophosphate pair follows a sequential steady-state mechanism. The product inhibition patterns of ATP and phosphate versus phosphoenolpyruvate were noncompetitive and uncompetitive, respectively, suggesting that these products were released in an ordered process (phosphate before ATP). The ordered release of phosphate and ATP and the noncompetitive inhibition patterns of pyruvate versus AMP and versus pyrophosphate also supported the sequential kinetic mechanism between AMP and pyrophosphate. Taken together, our data provide evidence for a uni uni bi bi pingpong mechanism for recombinant pyruvate phosphate dikinase from E. histolytica. The Delta G value for the reaction catalyzed by pyruvate phosphate dikinase (+2.7 kcal/mol) determined under near physiological conditions indicates that the synthesis of ATP is not thermodynamically favorable in trophozoites of E. histolytica.

Adenosine Monophosphate↗

PubMed2005

Pyruvate kinase revisited: the activating effect of K+.

For more than 50 years, it has been known that K(+) is an essential activator of pyruvate kinase (Kachmar, J. F., and Boyer, P. D. (1953) J. Biol. Chem. 200, 669-683). However, the role of K(+) in the catalysis by pyruvate kinase has not been totally understood. Previous studies without K(+) showed that the affinity of ADP-Mg(2+) depends on the concentration of phosphoenolpyruvate, although the kinetics of the enzyme at saturating K(+) concentrations show independence in the binding of substrates (Reynard, A. M., Hass, L. F., Jacobsen, D. D. & Boyer, P. D. (1961) J. Biol. Chem. 236, 2277-2283). Here, we explored the kinetics of the enzyme with and without K(+). The results show that without K(+), the kinetic mechanism of pyruvate kinase changes from random to ordered with phosphoenol-pyruvate as first substrate. V(max) with K(+) was about 400 higher than without K(+). In the presence of K(+), the affinities for phosphoenol-pyruvate, ADP-Mg(2+), oxalate, and ADP-Cr(2+) were 2-6-fold higher than in the absence of K(+). This as well as fluorescence data also indicate that K(+) is involved in the acquisition of the active conformation of the enzyme, allowing either phosphoenolpyruvate or ADP to bind independently (random mechanism). In the absence of K(+), ADP cannot bind to the enzyme until phosphoenolpyruvate forms a competent active site (ordered mechanism). We propose that K(+) induces the closure of the active site and the arrangement of the residues involved in the binding of the nucleotide.

Enzyme Activation↗

PubMed2006

Estrogen-related receptors stimulate pyruvate dehydrogenase kinase isoform 4 gene expression.

The pyruvate dehydrogenase complex (PDC) catalyzes the conversion of pyruvate to acetyl-CoA in mitochondria and is a key regulatory enzyme in the oxidation of glucose to acetyl-CoA. Phosphorylation of PDC by the pyruvate dehydrogenase kinases (PDK2 and PDK4) inhibits PDC activity. Expression of the PDK genes is elevated in diabetes, leading to the decreased oxidation of pyruvate to acetyl-CoA. In these studies we have investigated the transcriptional regulation of the PDK4 gene by the estrogen-related receptors (ERRalpha and ERRgamma). The ERRs are orphan nuclear receptors whose physiological roles include the induction of fatty acid oxidation in heart and muscle. Previously, we found that the peroxisome proliferator-activated receptor gamma coactivator (PGC-1alpha) stimulates the expression of PDK4. Here we report that ERRalpha and ERRgamma stimulate the PDK4 gene in hepatoma cells, suggesting a novel role for ERRs in controlling pyruvate metabolism. In addition, both ERR isoforms recruit PGC-1alpha to the PDK4 promoter. Insulin, which decreases the expression of the PDK4 gene, inhibits the induction of PDK4 by ERRalpha and ERRgamma. The forkhead transcription factor (FoxO1) binds the PDK4 gene and contributes to the induction of PDK4 by ERRs and PGC-1alpha. Insulin suppresses PDK4 expression in part through the dissociation of FoxO1 and PGC-1alpha from the PDK4 promoter. Our data demonstrate a key role for the ERRs in the induction of hepatic PDK4 gene expression.

3-Phosphoinositide-Dependent Protein Kinases↗

PubMed2002

Antioxidant alpha-keto-carboxylate pyruvate protects low-density lipoprotein and atherogenic macrophages.

Oxidative modification of low-density lipoprotein (oxLDL) plays a pathogenic role in atherogenesis. Classical antioxidants such as L-ascorbic acid can inhibit formation of oxLDL. Alpha-Keto-carboxylates such as pyruvate and congeners also display antioxidant properties in some cell-free and intact cell systems. We tested the hypothesis that pyruvate or alpha-keto-glutarate may function as antioxidants with respect to LDL incubated with 5 or 10 microM Cu2+ alone or in combination with THP-1-derived macrophages. alpha-Hydroxy-carboxylates (L-lactate), linear aliphatic monocarboxylates (acetate/caprylate) and L-ascorbic acid served as controls. The oxLDL formation was ascertained by electrophoretic mobility and oxLDL cytotoxicity was judged by macrophage viability and thiobarbituric acid reactive substances (TBARS) formation. Cu2+ alone was not cytotoxic but increased electrophoretic mobility of cell-free LDL, stimulating TBARS. Millimolar pyruvate, alpha-ketoglutarate, or micromolar L-ascorbic acid partially inhibited oxLDL formation, while alpha-hydroxy-carboxylate or the aliphatic mono-carboxylates had no measurable antioxidant properties in cell-free LDL. Co-culture of LDL with macrophages and Cu2+ augmented TBARS release and resulted in 95% macrophage death. Pyruvate improved macrophage viability with 5 microM Cu2+ up to 60%. L-Ascorbic acid (> or = 100 microM) protected macrophages up to 80%. When > or = 100 microM L-ascorbic acid was combined with pyruvate, oxLDL formation and macrophage death were fully prevented. Thus, alpha-keto-carboxylates, but not physiological alpha-hydroxy-carboxylates or aliphatic monocarboxylates qualify as antioxidants in LDL systems. Since alpha-keto-carboxylates enhanced the antioxidant power of L-ascorbic acid, our findings may have implications for strategies attenuating atherosclerosis.

Antioxidants↗

PubMed2001

Glucose and pyruvate metabolism of preimplantation goat blastocysts following in vitro fertilization and parthenogenetic activation.

The energy metabolism of preimplantation embryos can be used to predict viability and postimplantation development. Although preimplantation development and mean blastocyst cell numbers of goat in vitro-fertilized (IVF) embryos and chemically activated parthenogenotes are comparable, mammalian parthenogenotes are not viable, with most dying shortly after implantation. The objective of this study was to compare glucose and pyruvate metabolism of IVF goat blastocysts with that of parthenogenetic blastocysts developing from chemically activated oocytes. Embryos derived from IVF and parthenogenotes produced by exposing oocytes to either ionomycin or ethanol followed by 6-dimethylaminopurine (6-DMAP) were cultured in G1.2/G2.2 sequential culture media. Metabolism was determined for individual blastocysts using [5-3H]glucose and [2-14C]pyruvate to determine glycolytic and Kreb's cycle activity, respectively. Data were analyzed by ANOVA. A significantly higher percentage of activated oocytes underwent cleavage and developed to the blastocyst stage compared to IVF oocytes (p < 0.05). There was no significant difference in glucose or pyruvate metabolism between IVF and parthenogenetically activated blastocysts. Mean glucose metabolism through glycolysis was 154.9 +/- 29.1, 130.3 +/- 17.1, and 129 +/- 16.5 pmol/embryo/3 h for IVF, ethanol-activated, and ionomycin-activated blastocysts, respectively. Mean pyruvate metabolism through the Kreb's cycle was 28.1 +/- 8.0, 15.8 +/- 4.2, and 24.4 +/- 4.4 in pmol/embryo/3 h for IVF, ethanol-activated, and ionomycin-activated blastocysts, respectively. Our results suggest that known differences in postimplantation development observed in IVF versus parthenogenetic embryos cannot be attributed to differences in pyruvate or glucose metabolism in the preimplantation blastocysts. Thus, these activation protocols result in embryos capable of appropriate regulation of key metabolic enzymes.

Adenine↗

PubMed2004

Purification, characterization, cloning and expression of pyruvate decarboxylase from Torulopsis glabrata IFO005.

In the production of pyruvate and optically active alpha-hydroxy ketones by Torulopsis glabrata, pyruvate decarboxylase (PDC, EC 4.1.1.1) plays an important role in pyruvate metabolism and in catalyzing the biotransformation of aromatic amino acid precursors to alpha-hydroxy ketones. In this paper, we have purified and characterized PDC from T. glabrata IFO005 and cloned the corresponding gene. A simple, rapid and efficient purification protocol was developed that provided PDC with high specific activity. Unlike other yeast or higher plant enzymes, known as homotetramers (alpha(4) or beta(4)) or heterotetramers (alpha(2)beta(2)), two active isoforms of PDC purified from T. glabrata IFO005 were homodimeric proteins with subunits of 58.7 kDa. We isolated the T. glabrata PDC gene encoding 563 amino acid residues and succeeded in overproducing the recombinant PDC protein in Escherichia coli, in which the product amounted to about 10-20% of the total protein of the cell extract. Recombinant PDC from E. coli was purified as a homotetramer. Targeted gene disruption of PDC confirmed that T. glabrata has only one gene of PDC. This PDC gene showed about 80% homology with the genes of other yeasts, and amino acid residues involved in the allosteric site for pyruvate in other yeast PDCs were conserved in T. glabrata PDC. Both native PDC and recombinant PDC were activated by pyruvate and exhibited sigmoidal kinetics similar to those of Saccharomyces cerevisiae and higher plants. They also exhibited the similar catalytic properties: low thermostability, similar pH stability and optimal pH, and complete inhibition by glyoxylate.

Allosteric Site↗

PubMed1989

Non-invasive measurement of glucose and pyruvate uptake by individual human oocytes and preimplantation embryos.

Pyruvate and glucose uptake by 73 individual human oocytes and preimplantation embryos was measured non-invasively, using an ultramicrofluorescence assay to analyse changes in substrate levels in microdroplets of culture medium. The uptake of both substrates was measured over successive daily incubations between days 1 (unfertilized oocytes) or 2 ('spare' embryos which were not transferred) and day 6 (day 0 = day of insemination). Under these conditions, 58% (25/43) of fertilized embryos with two pronuclei on day 1 developed to the blastocyst stage by day 6. The pyruvate uptake of these embryos increased from approximately 28 to a maximum of 40 pmol/embryo/h between days 2.5 and 4.5. Similarly, glucose uptake increased from approximately 8 to 14 pmol/embryo/h between days 2.5 and 4.5, but then increased further to 24 pmol/embryo/h on day 5 at the blastocyst stage. [corrected] The pyruvate uptake of fertilized embryos which arrested at cleavage stages was significantly lower than for those which developed to the blastocyst stage. Polyspermic and parthenogenetic embryos, and unfertilized oocytes also had lower pyruvate uptakes at later stages. The glucose uptake of unfertilized oocytes and abnormal embryos never reached the level of fertilized embryos at the blastocyst stage on day 5.5. Non-invasive measurement of pyruvate uptake before embryo transfer may provide a valuable functional criterion for the selection of viable embryos capable of developing to the blastocyst stage.

Blastocyst↗

PubMed2000

Lactate regulates pyruvate uptake and metabolism in the preimplantation mouse embryo.

This study was an investigation of the interaction of lactate on pyruvate and glucose metabolism in the early mouse embryo. Pyruvate uptake and metabolism by mouse embryos were significantly affected by increasing the lactate concentration in the culture medium. In contrast, glucose uptake was not affected by lactate in the culture medium. At the zygote stage, the percentage of pyruvate taken up and oxidized was significantly reduced in the presence of increasing lactate, while at the blastocyst stage, increasing the lactate concentration increased the percentage of pyruvate oxidized. Lactate oxidation was determined to be 3-fold higher (when lactate was present at 20 mM) at the blastocyst stage compared to the zygote. Analysis of the kinetics of lactate dehydrogenase (LDH) determined that while the V(max) of LDH was higher at the zygote stage, the K(m) of LDH was identical for both stages of development, confirming that the LDH isozyme was the same. Furthermore, the activity of LDH isolated from both stages was reduced by 40% in the presence of 20 mM lactate. The observed differences in lactate metabolism between the zygote and blastocyst must therefore be attributed to in situ regulation of LDH. Activity of isolated LDH was found to be affected by nicotinamide adenine dinucleotide(+) (NAD(+)) concentration. In the presence of increasing concentrations of lactate, zygotes exhibited an increase in autofluorescence consistent with a depletion of NAD(+) in the cytosol. No increase was observed for later-stage embryos. Therefore it is proposed that the differences in pyruvate and lactate metabolism at the different stages of development are due to differences in the in situ regulation of LDH by cytosolic redox potential.

Animals↗

PubMed2005

Pyruvate modulates hepatic mitochondrial functions and reduces apoptosis indicators during hemorrhagic shock in rats.

BACKGROUND: Dysfunctional mitochondria have been widely accepted as one of the key targets and a mediator of secondary cell injury and organ failure during hemorrhagic shock (HS). The liver is known to be the first organ to display the signs of injury during HS. This report describes experiments to determine whether modulation of hepatic mitochondrial dysfunctions by pharmacologic agents could prevent liver injury in rats subjected to HS. METHODS: In this study, Sprague-Dawley rats were either treated as controls or subjected to computer-controlled arterial hemorrhage (40 mmHg) for 60 min followed by resuscitation with hypertonic saline, hypertonic beta-hydroxybutyrate, or hypertonic sodium pyruvate for the next 60 min before death. During the course of the experiment, animals were continuously monitored for hemodynamic and metabolic parameters. At the end of the experiment, the liver was excised and examined for oxidative injury, mitochondrial functions, expression of nitric oxide synthase, and indicators of apoptosis. RESULTS: In comparison to hypertonic saline and hypertonic beta-hydroxybutyrate, pyruvate significantly protected the liver from oxidative injury, prevented the up-regulation of nitric oxide synthase, inhibited pyruvate dehydrogenase deactivation, and improved cellular energy charge and mitochondrial functions. In addition, pyruvate also reduced cleavage of poly-adenosine diphosphate ribose polymerase by preventing leakage of mitochondrial cytochrome c in the liver of HS animals. CONCLUSIONS: These data suggest that modulation of mitochondrial metabolic functions is likely to be one of the important mechanisms by which pyruvate exerts its protective effects on the liver during HS and resuscitation in rats.

Animals↗

PubMed2000

Cerebral metabolism of lactate in vivo: evidence for neuronal pyruvate carboxylation.

The cerebral metabolism of lactate was investigated. Awake mice received [3-13C]lactate or [1-13C]glucose intravenously, and brain and blood extracts were analyzed by 13C nuclear magnetic resonance spectroscopy. The cerebral uptake and metabolism of [3-13C]lactate was 50% that of [1-13C]glucose. [3-13C]Lactate was almost exclusively metabolized by neurons and hardly at all by glia, as revealed by the 13C labeling of glutamate, gamma-aminobutyric acid and glutamine. Injection of [3-13C]lactate led to extensive formation of [2-13C]lactate, which was not seen with [1-13C]glucose, nor has it been seen in previous studies with [2-13C]acetate. This formation probably reflected reversible carboxylation of [3-13C]pyruvate to malate and equilibration with fumarate, because inhibition of succinate dehydrogenase with nitropropionic acid did not block it. Of the [3-13C]lactate that reached the brain, 20% underwent this reaction, which probably involved neuronal mitochondrial malic enzyme. The activities of mitochondrial malic enzyme, fumarase, and lactate dehydrogenase were high enough to account for the formation of [2-13C]lactate in neurons. Neuronal pyruvate carboxylation was confirmed by the higher specific activity of glutamate than of glutamine after intrastriatal injection of [1-14C]pyruvate into anesthetized mice. This procedure also demonstrated equilibration of malate, formed through pyruvate carboxylation, with fumarate. The demonstration of neuronal pyruvate carboxylation demands reconsideration of the metabolic interrelationship between neurons and glia.

Animals↗

PubMed2001

The antioxidant potential of pyruvate in the amitochondriate diplomonads Giardia intestinalis and Hexamita inflata.

Giardia intestinalis and Hexamita inflata are microaerophilic protozoa which rely on fermentative metabolism for energy generation. These organisms have developed a number of antioxidant defence strategies to cope with elevated O(2) tensions which are inimical to survival. In this study, the ability of pyruvate, a central component of their energy metabolism, to act as a physiological antioxidant was investigated. The intracellular pools of 2-oxo acids in G. intestinalis were determined by HPLC. With the aid of a dichlorodihydrofluorescein diacetate-based assay, intracellular reactive oxygen species generation by G. intestinalis and H. inflata suspensions was monitored on-line. Addition of physiologically relevant concentrations of pyruvate to G. intestinalis and H. inflata cell suspensions was shown to attenuate the rate of H(2)O(2)- and menadione-induced generation of reactive oxygen species. In addition, pyruvate was also shown to decrease the generation of low-level chemiluminescence arising from the oxygenation of anaerobic suspensions of H. inflata. In contrast, addition of pyruvate to suspensions of respiring Saccharomyces cerevisiae was shown to increase the generation of reactive oxygen species. These data suggest that (i) in G. intestinalis and H. inflata, pyruvate exerts antioxidant activity at physiological levels, and (ii) it is the absence of a respiratory chain in the diplomonads which facilitates the observed antioxidant activity.

Animals↗

PubMed2001

Production of the Gram-positive Sarcina ventriculi pyruvate decarboxylase in Escherichia coli.

Sarcina ventriculi grows in a remarkable range of mesophilic environments from pH 2 to pH 10. During growth in acidic environments, where acetate is toxic, expression of pyruvate decarboxylase (PDC) serves to direct the flow of pyruvate into ethanol during fermentation. PDC is rare in bacteria and absent in animals, although it is widely distributed in the plant kingdom. The pdc gene from S. ventriculi is the first to be cloned and characterized from a Gram-positive bacterium. In Escherichia coli, the recombinant pdc gene from S. ventriculi was poorly expressed due to differences in codon usage that are typical of low-G+C organisms. Expression was improved by the addition of supplemental codon genes and this facilitated the 136-fold purification of the recombinant enzyme as a homo-tetramer of 58 kDa subunits. Unlike Zymomonas mobilis PDC, which exhibits Michaelis-Menten kinetics, S. ventriculi PDC is activated by pyruvate and exhibits sigmoidal kinetics similar to fungal and higher plant PDCs. Amino acid residues involved in the allosteric site for pyruvate in fungal PDCs were conserved in S. ventriculi PDC, consistent with a conservation of mechanism. Cluster analysis of deduced amino acid sequences confirmed that S. ventriculi PDC is quite distant from Z. mobilis PDC and plant PDCs. S. ventriculi PDC appears to have diverged very early from a common ancestor which included most fungal PDCs and eubacterial indole-3-pyruvate decarboxylases. These results suggest that the S. ventriculi pdc gene is quite ancient in origin, in contrast to the Z. mobilis pdc, which may have originated by horizontal transfer from higher plants.

Amino Acid Sequence↗

PubMed1976

Pyruvic acid as an etching agent.

Phosphoric acid at different concentrations has been extensively used as an etching agent to improve bonding of dental materials to enamel surfaces. Recently attention has been drawn to the possible use of polyfunctional organic acids as conditioning agents. The object of this investigation was to determine the optimal concentration of pyruvic acid as an etching agent. A commercial composite resin with an intermediary bonding system supplied with 37% H3PO4 as an etching agent was used as the control system. In addition, a comparative study was carried out to evaluate 37% H3PO4, 20% lactic acid and the optimal concentration of pyruvic acid as conditioning solutions. Etching enamel surfaces with 10% pyruvic acid resulted in the optimal tensile bond strength of the resin to etched enamel surfaces. The use of 10% pyruvic acid did not adversely affect the bond strength of the resin system when compared to enamel surfaces etched with 37% H3PO4 for the same time period. Significantly lower tensile bond strengths were recorded on enamel surfaces etched with 20% lactic acid. The rate and depth of etching obtained with 37% H3PO4 can be considerably reduced by using 10% pyruvic acid as the conditioning agent.

Composite Resins↗

PubMed1977

Interrelationship in the regulation of pyruvate dehydrogenase and adenine-nucleotide translocase by palmitoyl-CoA in isolated mitochondria.

Full activation of rat liver pyruvate dehydrogenase in vitro by ADP was prevented by palmitoyl-CoA at a concentration sufficiently low to preclude substrate effects secondary to its oxidation by mitochondria. Activation of pyruvate dehydrogenase by ADP in livers of fat-fed rats was less than in the control animal. The results are consistent with the experiments demonstrating an inhibition of adenine nucleotide translocase and on increased intramitochondrial ATP/ADP ratio by palmitoyl-CoA which could account for the effect on pyruvate dehydrogenase. Inactivation of brain pyruvate dehydrogenase by ATP was also diminished by palmitoyl-CoA indicating that the effect was at the level of the adenine nucleotides rather than at either the pyruvate dehydrogenase kinase or phosphatase enzymes.

Adenosine Diphosphate↗

PubMed1977

Carbon-14 tracer studies in rat-liver perfusion experiments under conditions of gluconeogenesis from lactate and pyruvate.

The intracellular events in the metabolic pathway of gluconeogenesis from lactate and pyruvate in liver tissue were assumed to be understood. Nevertheless the results of several 14C-tracer experiments gave rise to the postulation of still unknown intracellular interactions under this condition. We have tried to contribute to the solution of this problem by using different 14C labeled tracers such as [1-14C]lactate or pyruvate and [2-14C]lactate or pyruvate, [14C]bicarbonate and [1-14C]octanoate in perfusion experiments with livers from rats under conditions of gluconeogenesis from lactate and pyruvate. The 14C labeling patterns of intracellular metabolites as malate, citrate, phosphoenolpyruvate, phosphoglycerate and newly synthesized glucose were analysed under different conditions. A comparison with values calculated by using metabolic models, based on the generally accepted concepts of intracellular interactions, showed some fundamental discrepancies, which justify the postulation of still unknown intracellular interactions in the pathway of gluconeogenesis from lactate and pyruvate.

Acetoacetates↗