Showing papers on "Pyruvate dehydrogenase kinase published in 2003"
TL;DR: Recent significant advances in knowledge of the mechanisms regulating PDC are summarized, with emphasis on the PDKs, in particular PDK4, whose expression is linked with sustained changes in tissue lipid handling and which may represent an attractive target for pharmacological interventions aimed at modulating whole body glucose, lipid, and lactate homeostasis in disease states.
Abstract: The mitochondrial pyruvate dehydrogenase complex (PDC) catalyzes the oxidative decarboxylation of pyruvate, linking glycolysis to the tricarboxylic acid cycle and fatty acid (FA) synthesis. Knowledge of the mechanisms that regulate PDC activity is important, because PDC inactivation is crucial for glucose conservation when glucose is scarce, whereas adequate PDC activity is required to allow both ATP and FA production from glucose. The mechanisms that control mammalian PDC activity include its phosphorylation (inactivation) by a family of pyruvate dehydrogenase kinases (PDKs 1-4) and its dephosphorylation (activation, reactivation) by the pyruvate dehydrogenase phosphate phosphatases (PDPs 1 and 2). Isoform-specific differences in kinetic parameters, regulation, and phosphorylation site specificity of the PDKs introduce variations in the regulation of PDC activity in differing endocrine and metabolic states. In this review, we summarize recent significant advances in our knowledge of the mechanisms regulating PDC with emphasis on the PDKs, in particular PDK4, whose expression is linked with sustained changes in tissue lipid handling and which may represent an attractive target for pharmacological interventions aimed at modulating whole body glucose, lipid, and lactate homeostasis in disease states.
476 citations
TL;DR: The concept that thePDKs act as tissue homoeostats is developed and it is suggested that long-term modulation of expression of individual PDKs, particularly PDK4, is an essential component of allostasis to maintain Homoeostasis.
Abstract: PDC (pyruvate dehydrogenase complex) catalyses the oxidative decarboxylation of pyruvate, linking glycolysis to the tricarboxylic acid cycle. Regulation of PDC determines and reflects substrate preference and is critical to the ‘glucose–fatty acid cycle’, a concept of reciprocal regulation of lipid and glucose oxidation to maintain glucose homoeostasis developed by Philip Randle. Mammalian PDC activity is inactivated by phosphorylation by the PDKs (pyruvate dehydrogenase kinases). PDK inhibition by pyruvate facilitates PDC activation, favouring glucose oxidation and malonyl-CoA formation: the latter suppresses LCFA (long-chain fatty acid) oxidation. PDK activation by the high mitochondrial acetyl-CoA/CoA and NADH/NAD + concentration ratios that reflect high rates of LCFA oxidation causes blockade of glucose oxidation. Complementing glucose homoeostasis in health, fuel allostasis, i.e. adaptation to maintain homoeostasis, is an essential component of the response to chronic changes in glycaemia and lipidaemia in insulin resistance. We develop the concept that the PDKs act as tissue homoeostats and suggest that long-term modulation of expression of individual PDKs, particularly PDK4, is an essential component of allostasis to maintain homoeostasis. We also describe the intracellular signals that govern the expression of the various PDK isoforms, including the roles of the peroxisome proliferator-activated receptors and lipids, as effectors within the context of allostasis.
414 citations
TL;DR: The pyruvate dehydrogenase complex (PDC) is subjected to multiple interacting levels of control in plant cells, and the two different forms of the complex are regulated by distinct organelle-specific mechanisms.
Abstract: The pyruvate dehydrogenase complex (PDC) is subjected to multiple interacting levels of control in plant cells. The first level is subcellular compartmentation. Plant cells are unique in having two distinct, spatially separated forms of the PDC; mitochondrial (mtPDC) and plastidial (plPDC). The mtPDC is the site of carbon entry into the tricarboxylic acid cycle, while the plPDC provides acetyl-CoA and NADH for de novo fatty acid biosynthesis. The second level of regulation of PDC activity is the control of gene expression. The genes encoding the subunits of the mt- and plPDCs are expressed following developmental programs, and are additionally subject to physiological and environmental cues. Thirdly, both the mt- and plPDCs are sensitive to product inhibition, and, potentially, to metabolite effectors. Finally, the two different forms of the complex are regulated by distinct organelle-specific mechanisms. Activity of the mtPDC is regulated by reversible phosphorylation catalyzed by intrinsic kinase and phosphatase components. An additional level of sensitivity is provided by metabolite control of the kinase activity. The plPDC is not regulated by reversible phosphorylation. Instead, activity is controlled to a large extent by the physical environment that exists in the plastid stroma.
263 citations
28 Nov 2003
TL;DR: The current status of knowledge of the biochemical, regulatory, structural, genomic, and evolutionary aspects of these fascinating multienzyme complexes are reviewed.
Abstract: ▪ Abstract Plant cells are unique in that they contain four species of α-ketoacid dehydrogenase complex: plastidial pyruvate dehydrogenase, mitochondrial pyruvate dehydrogenase, α-ketoglutarate (2-oxoglutarate) dehydrogenase, and branched-chain α-ketoacid dehydrogenase. All complexes include multiple copies of three components: an α-ketoacid dehydrogenase/decarboxylase, a dihydrolipoyl acyltransferase, and a dihydrolipoyl dehydrogenase. The mitochondrial pyruvate dehydrogenase complex additionally includes intrinsic regulatory protein-kinase and -phosphatase enzymes. The acyltransferases form the intricate geometric core structures of the complexes. Substrate channeling plus active-site coupling combine to greatly enhance the catalytic efficiency of these complexes. These α-ketoacid dehydrogenase complexes occupy key positions in intermediary metabolism, and a basic understanding of their properties is critical to genetic and metabolic engineering. The current status of knowledge of the biochemical, regul...
157 citations
TL;DR: A model for the flip-flop action of this enzyme is proposed through a concerted ∼2-Å shuttle-like motion of its heterodimers, suggesting that this newly defined shuttle- like motion of domains is common to the family of thiamin pyrophosphate-dependent enzymes.
144 citations
TL;DR: Results strongly indicate that the hemB mutant generates ATP from glucose or fructose only by substrate phosphorylation, which is consistent with previous reports.
Abstract: The high-resolution two-dimensional (2D) protein gel electrophoresis technique combined with matrix-assisted laser desorption ionization-time of flight mass spectrometry was used for identification of proteins whose levels were changed by a mutation in hemB. Cytoplasmic protein extracts obtained from the mutant and the wild type (strain COL) at different stages of growth in tryptone soya broth (exponential, transitional, and stationary growth phases) were separated on 2D protein gels. Comparison of the 2D patterns of the protein extracts of the two strains revealed major differences. Because the electron transport chain of the mutant is interrupted due to the deficiency of heme, this organism should be unable to use oxygen or nitrate as a terminal electron acceptor. Consistent with this hypothesis, proteins involved in the glycolytic pathway and related pathways (glyceraldehyde-3-phosphate dehydrogenase, enolase, and phosphoglycerate kinase) and in fermentation pathways (lactate dehydrogenase, alcohol dehydrogenase, and pyruvate formate lyase) were induced in exponentially growing cells of the mutant. These results strongly indicate that the hemB mutant generates ATP from glucose or fructose only by substrate phosphorylation. Analyses of the fermentation reactions showed that the main product was lactate. Although pyruvate formate lyase (Pfl) and pyruvate dehydrogenase were present, neither ethanol nor acetate was detected in significant amounts. Presumably, Pfl was not activated in the presence of oxygen, and pyruvate dehydrogenase might have very low activity. Transcriptional analysis of citB, encoding the aconitase, revealed that the activity of the citrate cycle enzymes was down-regulated in the hemB mutant. The arginine deiminase pathway was also induced, and it could provide ATP as well. Furthermore, the amounts of most of the extracellular virulence factors were significantly reduced by a mutation in hemB, which is consistent with previous reports.
134 citations
TL;DR: Findings indicate that opposite changes in expression of specific PDK and PDP isoenzymes contribute to hyperphosphorylation and therefore inactivation of the PDC in heart and kidney during starvation and diabetes.
Abstract: The pyruvate dehydrogenase complex (PDC) is inactivated in many tissues during starvation and diabetes to conserve three-carbon compounds for gluconeogenesis. This is achieved by an increase in the extent of PDC phosphorylation caused in part by increased pyruvate dehydrogenase kinase (PDK) activity due to increased PDK expression. This study examined whether altered pyruvate dehydrogenase phosphatase (PDP) expression also contributes to changes in the phosphorylation state of PDC during starvation and diabetes. Of the two PDP isoforms expressed in mammalian tissues, the Ca 2+ -sensitive isoform (PDP1) is highly expressed in rat heart, brain, and testis and is detectable but less abundant in rat muscle, lung, kidney, liver, and spleen. The Ca 2+ -insensitive isoform (PDP2) is abundant in rat kidney, liver, heart, and brain and is detectable in spleen and lung. Starvation and streptozotocin-induced diabetes cause decreases in PDP2 mRNA abundance, PDP2 protein amount, and PDP activity in rat heart and kidney. Refeeding and insulin treatment effectively reversed these effects of starvation and diabetes, respectively. These findings indicate that opposite changes in expression of specific PDK and PDP isoenzymes contribute to hyperphosphorylation and therefore inactivation of the PDC in heart and kidney during starvation and diabetes.
124 citations
TL;DR: A number of therapeutic targets are currently under investigation for inhibition of hepatic glucose production with small molecules, some of which have been validated by compounds that are effective in animal models.
Abstract: A number of therapeutic targets are currently under investigation for inhibition of hepatic glucose production with small molecules. Antagonists of the glucagon receptor, glycogen phosphorylase, 11-beta-hydroxysteroid dehydrogenase-1 and fructose 1,6-bisphosphatase are, or have been, under evaluation in human clinical trials. Other strategies, including glucocorticoid receptor antagonists and carnitine palmitoyltransferase inhibitors, are supported by proof of principle studies in man as well as rodents. Several potential targets including glucose-6-phosphatase, glucose-6-phosphatase translocase, glycogen synthase kinase-3, adenosine receptor 2B antagonists, phosphoenolpyruvate carboxykinase and pyruvate dehydrogenase kinase, have been validated by compounds that are effective in animal models. Other targets like PGC-1a and CREB have initial validation support but no medicinal chemistry has been reported.
85 citations
TL;DR: Recent developments concerning the structure-function relationship of this multienzyme complex from various organisms are discussed with emphasis on regulatory aspects of the mammalian complex.
81 citations
TL;DR: The differential effects of insulin and DCA on pyruvate and lactate oxidation provide further evidence for compartmentation of cardiac carbohydrate metabolism.
Abstract: 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...
81 citations
TL;DR: Comparison of pyruvate accumulation in six strains of Escherichia coli and their corresponding ppc mutants found lactate was an unexpected by-product even though measured lactate dehydrogenase (LDH) activity was very low.
Abstract: We compared pyruvate accumulation in six strains of Escherichia coli and their corresponding ppc mutants. Each strain contained a mutation of a gene involved in the pathway to acetate synthesis. Strains with mutations in genes encoding the pyruvate dehydrogenase complex generally exhibited the greatest pyruvate accumulation of which CGSC6162 (an aceF mutant) and CGSC6162 Δppc were studied in greater detail in controlled fermenters. Both CGSC6162 and CGSC6162 Δppc accumulated greater than 35 g/l pyruvate in a medium supplemented with acetate. We observed pyruvate mass yields from glucose of 0.72 in CGSC6162, with volumetric productivities above 1.5 g l−1 h−1. For CGSC6162 Δppc, we observed pyruvate yields of 0.78 and volumetric productivities above 1.2 g l−1 h−1. CGSC6162 consumed all initially supplied acetate, while CGSC6162 Δppc first consumed and then generated acetate during the course of a 36 h fermentation. Acetate generation and pyruvate oxidase activity was pH- and temperature-dependent, with a pH of 7.0 and the lowest temperature studied (32°C) favoring the greatest pyruvate generation. Lactate was an unexpected by-product even though measured lactate dehydrogenase (LDH) activity was very low.
TL;DR: Evidence is described indicating that the alterations in glucose metabolism in hypertrophied hearts cannot be explained simply by changes in PDC expression or control, and mechanisms that may lead to an altered balance of pyruvate metabolism in cardiac hypertrophy are discussed.
Abstract: 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.
TL;DR: AZD7545 (10 mg/kg) twice daily for 7 days markedly improved the 24-h glucose profile, by eliminating the postprandial elevation in blood glucose, suggesting that PDHK inhibitors may be beneficial agents for improving glucose control in the treatment of type 2 diabetes.
Abstract: PDH (pyruvate dehydrogenase) is a key enzyme controlling the rate of glucose oxidation, and the availability of gluconeogenic precursors. Activation of PDH in skeletal muscle and liver may increase glucose uptake and reduce glucose production. This study describes the properties of AZD7545, a novel, small-molecule inhibitor of PDHK (PDH kinase). In the presence of PDHK2, AZD7545 increased PDH activity with an EC(50) value of 5.2 nM. In rat hepatocytes, the rate of pyruvate oxidation was stimulated 2-fold (EC(50) 105 nM). A single dose of AZD7545 to Wistar rats increased the proportion of liver PDH in its active, dephosphorylated form in a dose-related manner from 24.7 to 70.3% at 30 mg/kg; and in skeletal muscle from 21.1 to 53.3%. A single dose of 10 mg/kg also significantly elevated muscle PDH activity in obese Zucker (fa/fa) rats. Obese, insulin-resistant, Zucker rats show elevated postprandial glucose levels compared with their lean counterparts (8.7 versus 6.1 mM at 12 weeks old). AZD7545 (10 mg/kg) twice daily for 7 days markedly improved the 24-h glucose profile, by eliminating the postprandial elevation in blood glucose. These results suggest that PDHK inhibitors may be beneficial agents for improving glucose control in the treatment of type 2 diabetes.
TL;DR: This work has identified the yeast mitochondrial pyruvate carrier by measuring inhibitor-sensitive pyruVate uptake into mitochondria from 18 different Saccharomyces cerevisiae mutants, each lacking an unattributed member of the mitochondrial carrier family (MCF).
Abstract: Mitochondrial pyruvate transport is fundamental for metabolism and mediated by a specific inhibitable carrier. We have identified the yeast mitochondrial pyruvate carrier by measuring inhibitor-sensitive pyruvate uptake into mitochondria from 18 different Saccharomyces cerevisiae mutants, each lacking an unattributed member of the mitochondrial carrier family (MCF). Only mitochondria from the YIL006w deletion mutant exhibited no inhibitor-sensitive pyruvate transport, but otherwise behaved normally. YIL006w encodes a 41.9 kDa MCF member with homologous proteins present in both the human and mouse genomes.
TL;DR: Results are consistent with a defect of mitochondrial pyruvate transport in the patient, which presented at birth with hypotonia, mild facial dysmorphism, periventricular cysts, marked metabolic acidosis, hyperlactacidemia and delivery at 37w of a healthy female, who is currently 2-month old.
TL;DR: The results suggest that there are two pathways for PyrKinc modification at the post-translational level: one involves partial C-terminal truncation to generate a 51 kDa pyruvate kinase subunit which might have altered regulatory properties and the other involves phosphorylation and ubiquitin conjugation that targets the protein to the 26S proteasome for complete degradation.
Abstract: Cytosolic pyruvate kinase (ATP:pyruvate 2-O-phosphotransferase, EC 2.7.1.40) is an important glycolytic enzyme, but the post-translational regulation of this enzyme is poorly understood. Sequence analysis of the soybean seed enzyme suggested the potential for two phosphorylation sites: site-1 (FVRKGS 220 DLVN) and site-2 (VLTRGGS 407 TAKL). Sequence- and phosphorylation state-specific antipeptide antibodies established that cytosolic pyruvate kinase (PyrKin c ) is phosphorylated at both sites in vivo. However, by SDS-PAGE, the phosphorylated polypeptides were found to be smaller (20-51 kDa) than the full length (55 kDa). Biochemical separations of seed proteins by size exclusion chromatography and sucrose-density gradient centrifugation revealed that the phosphorylated polypeptides were associated with 26S proteasomes. The 26S proteasome particle in developing seeds was determined to be of approximately 1900 kDa. In vitro, the 26S proteasome degraded associated PyrKin c polypeptides, and this was blocked by proteasome-specific inhibitors such as MG132 and NLVS. By immunoprecipitation, we found that some part of the phosphorylated PyrKin c was conjugated to ubiquitin and shifted to high molecular mass forms in vivo. Moreover, recombinant wild-type PyrKin c was ubiquitinated in vitro to a much greater extent than the S220A and S407A mutant proteins, suggesting a link between phosphorylation and ubiquitination In addition, during seed development, a progressive accumulation of a C-terminally truncated polypeptide of approximately 51 kDa was observed that was in parallel with a loss of the full-length 55 kDa polypeptide. Interestingly, the C-terminal 51 kDa truncation showed not only pyruvate kinase activity but also activation by aspartate. Collectively, the results suggest that there are two pathways for PyrKin c modification at the post-translational level. One involves partial C-terminal truncation to generate a 51 kDa pyruvate kinase subunit which might have altered regulatory properties and the other involves phosphorylation and ubiquitin conjugation that targets the protein to the 26S proteasome for complete degradation.
TL;DR: Heterodimerization partners for retinoid X receptors (RXRs) include PPARalpha and thyroid-hormone receptors (TRs) and results indicate that hepatic PDK4 up-regulation can be achieved by heterodimerizing of either PPAR Alpha or TR with the RXR receptor and that effects of PPAR alpha activation on hepaticPDK2 and PDK 4 expression favour a switch towards preferential expression of PDK2.
Abstract: Liver contains two pyruvate dehydrogenase kinases (PDKs), namely PDK2 and PDK4, which regulate glucose oxidation through inhibitory phosphorylation of the pyruvate dehydrogenase complex (PDC). Starvation increases hepatic PDK2 and PDK4 protein expression, the latter occurring, in part, via a mechanism involving peroxisome proliferator-activated receptor-alpha (PPARalpha). High-fat feeding and hyperthyroidism, which increase circulating lipid supply, enhance hepatic PDK2 protein expression, but these increases are insufficient to account for observed increases in hepatic PDK activity. Enhanced expression of PDK4, but not PDK2, occurs in part via a mechanism involving PPAR-alpha. Heterodimerization partners for retinoid X receptors (RXRs) include PPARalpha and thyroid-hormone receptors (TRs). We therefore investigated the responses of hepatic PDK protein expression to high-fat feeding and hyperthyroidism in relation to hepatic lipid delivery and disposal. High-fat feeding increased hepatic PDK2, but not PDK4, protein expression whereas hyperthyroidism increased both hepatic PDK2 and PDK4 protein expression. Both manipulations decreased the sensitivity of hepatic carnitine palmitoyltransferase I (CPT I) to suppression by malonyl-CoA, but only hyperthyrodism elevated plasma fatty acid and ketone-body concentrations and CPT I maximal activity. Administration of the selective PPAR-alpha activator WY14,643 significantly increased PDK4 protein to a similar extent in both control and high-fat-fed rats, but WY14,643 treatment and hyperthyroidism did not have additive effects on hepatic PDK4 protein expression. PPARalpha activation did not influence hepatic PDK2 protein expression in euthyroid rats, suggesting that up-regulation of PDK2 by hyperthyroidism does not involve PPARalpha, but attenuated the effect of hyperthyroidism to increase hepatic PDK2 expression. The results indicate that hepatic PDK4 up-regulation can be achieved by heterodimerization of either PPARalpha or TR with the RXR receptor and that effects of PPARalpha activation on hepatic PDK2 and PDK4 expression favour a switch towards preferential expression of PDK4.
TL;DR: The isoenzyme-selectivity profile of AZD7545 and related compounds is described and the consequences for their in vivo mode of action are discussed.
Abstract: The PDH (pyruvate dehydrogenase) multi-enzyme complex catalyses a key regulatory step in oxidative glycolysis. Phosphorylation of the E1 subunit of the complex on serine residues results in the inactivation of enzyme activity. A family of four dedicated PDH kinase isoenzymes exists, each of which displays a distinct tissue-specific expression profile. AZD7545 is one of a series of PDH kinase inhibitors developed for the treatment of type 2 diabetes. The isoenzyme-selectivity profile of AZD7545 and related compounds is described and the consequences for their in vivo mode of action are discussed.
TL;DR: This review emphasizes how the foremost changes in the kinase and phosphatase activities issue from the dynamic, effector-modified interactions of these regulatory enzymes with the flexibly held outer domains of the core-forming dihydrolipoyl acetyl transferase component.
Abstract: Four pyruvate dehydrogenase kinase and two pyruvate dehydrogenase phosphatase isoforms function in adjusting the activation state of the pyruvate dehydrogenase complex (PDC) through determining the fraction of active (nonphosphorylated) pyruvate dehydrogenase component. Necessary adaptations of PDC activity with varying metabolic requirements in different tissues and cell types are met by the selective expression and pronounced variation in the inherent functional properties and effector sensitivities of these regulatory enzymes. This review emphasizes how the foremost changes in the kinase and phosphatase activities issue from the dynamic, effector–modified interactions of these regulatory enzymes with the flexibly held outer domains of the core-forming dihydrolipoyl acetyl transferase component.
TL;DR: It is suggested that a partial reduction of the repression of the mtPDC by antisense PDHK expression can alter carbon flux and, in particular, the contribution of carbon moieties from pyruvate to fatty acid biosynthesis and storage lipid accumulation in developing seeds.
Abstract: Pyruvate dehydrogenase kinase (PDHK), a negative regulator of the mitochondrial pyruvate dehydrogenase complex (mtPDC), plays a pivotal role in controlling mtPDC activity, and hence, the TCA cycle and cell respiration. Previously, the cloning of a PDHK cDNA from Arabidopsis thaliana and the effects of constitutively down-regulating its expression on plant growth and development has been reported. The first detailed analyses of the biochemical and physiological effects of partial silencing of the mtPDHK in A. thaliana using antisense constructs driven by both constitutive and seed-specific promoters are reported here. The studies revealed an increased level of respiration in leaves of the constitutive antisense PDHK transgenics; an increase in respiration was also found in developing seeds of the seed-specific antisense transgenics. Both constitutive and seed-specific partial silencing of the mtPDHK resulted in increased seed oil content and seed weight at maturity. Feeding 3- 14 C pyruvate to bolted stems containing siliques (constitutive transgenics), or to isolated siliques or immature seeds (seed-specific transgenics) confirmed a higher rate of incorporation of radiolabel into all seed lipid species, particularly triacylglycerols. Neither constitutive nor seed-specific partial silencing of PDHK negatively affected overall silique and seed development. Instead, oil and seed yield, and overall plant productivity were improved. These findings suggest that a partial reduction of the repression of the mtPDC by antisense PDHK expression can alter carbon flux and, in particular, the contribution of carbon moieties from pyruvate to fatty acid biosynthesis and storage lipid accumulation in developing seeds, implicating a role for mtPDC in fatty acid biosynthesis in seeds.
TL;DR: Significant differences in the site-specificity displayed by PDP1c and PDP2c should be particularly important under conditions such as starvation and diabetes, which are associated with a great increase in phosphorylation of sites 2 and 3 of pyruvate dehydrogenase.
TL;DR: Results indicate that pyruvate could modulate key regulatory signal pathways in cytosol and mitochondrial matrix, thereby inactivating endothelial death pathways and suggested that stabilizing the expression of bcl-2 and bax genes by metabolic antioxidants may be an effective strategy for endothelial protection against oxidative stress.
TL;DR: Intracellular pyruvic acid and β-NADH appear to act in concert through glycolysis, to enhance H2O2 intracellular antioxidant capacity in neuroblastoma cells, and future research will be required to examine whether similar effects are observed in primary neuronal culture or intact tissue.
Abstract: Elevated production of hydrogen peroxide (H2O2) in the central nervous system has been implicated in the pathogenesis of several neurodegenerative diseases, including Parkinson's disease, ischemic reperfusion, stroke, and Alzheimer's disease. Pyruvic acid has a critical role in energy metabolism and a capability to nonenzymatically decarboxylate H2O2 into H2O. This study examined the effects of glycolytic regulation of pyruvic acid on H2O2 toxicity in murine neuroblastoma cells. Glycolytic energy substrates including D-(+)-glucose, D-(−) fructose and the adenosine transport blocker dipyridamole, were not effective in providing protection against H2O2 toxicity, negating energy as a factor. On the other hand, pyruvic acid completely prevented H2O2 toxicity, restoring the loss of ATP and cell viability. H2O2 toxicity was also attenuated by d-fructose 1,6 diphosphate (FBP), phospho (enol) pyruvate (PEP), niacinamide, β-nicotinamide adenine dinucleotide (β-NAD+), and reduced form (β-NADH). Both FBP and PEP exerted positive kinetic effects on pyruvate kinase (PK) activity. Interestingly, only pyruvic acid and β-NADH exhibited powerful stoichiometric H2O2 antioxidant properties. Further, β-NADH may exert positive effects on PK activity. Subsequent pyruvic acid accumulation can lead to the recycling of β-NAD1 through lactate dehydrogenase and β-NADH through glyceraldehyde-3-phosphate dehydrogenase. It was concluded from these studies that intracellular pyruvic acid and β-NADH appear to act in concert through glycolysis, to enhance H2O2 intracellular antioxidant capacity in neuroblastoma cells. Future research will be required to examine whether similar effects are observed in primary neuronal culture or intact tissue.
TL;DR: L-cysteine which is known to inhibit the activity of pyruvate kinase type M(2) from neoplastic cells transfering a phosphate from PEP to ADP, can act as a control factor champing the direction of enzymatic reaction in cancer cells.
Abstract: Pyruvate kinase type M2 from Morris hepatoma 7777 tumour cell nuclei and cytosol, in contrast to types L and M2 from nuclei and cytosol of normal rat liver, shows the histone H1 kinase activity. Moreover, in the presence of l-cysteine and without ADP it converts 2-phosphoenolpyruvate (PEP) to pyruvate while in the presence of l-arginine or l-histidine does not. l-Cysteine markedly stimulates the activity of histone H1 kinase transferring a phosphate group from PEP to, as results suggested, the e-amino group of l-lysine of histone H1. This, l-cysteine which is known to inhibit the activity of pyruvate kinase type M2 from neoplastic cells transfering a phosphate from PEP to ADP, can act as a control factor champing the direction of enzymatic reaction in cancer cells.
TL;DR: The single amino acid replacement of Tyr52 with Leu drastically increased the activity of Lactobacillus pentosus NAD-dependent D-lactate dehydrogenase toward larger aliphatic or aromatic 2-ketoacid substrates and decreased the activity toward pyruvate by about 30-fold, converting the enzyme into a highly active D-2-hydroxyisocaproate dehydrogensase.
Abstract: The single amino acid replacement of Tyr52 with Leu drastically increased the activity of Lactobacillus pentosus NAD-dependent D-lactate dehydrogenase toward larger aliphatic or aromatic 2-ketoacid substrates by 3 or 4 orders of magnitude and decreased the activity toward pyruvate by about 30-fold, converting the enzyme into a highly active D-2-hydroxyisocaproate dehydrogenase.
TL;DR: Data suggest that glucose oxidation rates in the heart can be dramatically altered independent of PDK phosphorylation and inhibition of PDC by PDK, and suggests that PPAR-alpha activation decreases glucose oxidation in hearts mainly by decreasing the flux of pyruvate through PDC due to negative feedback of P DC by fatty acid oxidation reaction products rather than by the phosphorylated state of the PDC complex.
Abstract: The pyruvate dehydrogenase enzyme complex (PDC) is rate limiting for glucose oxidation in the heart. Inhibition of PDC by end-product feedback and phosphorylation by pyruvate dehydrogenase kinase (...
TL;DR: Analytical ultracentrifugation studies established that the soluble PDK2 isoform is a stable dimer and reversible bifunctional binding to L2 with the mandatory singly held transition fits the proposed “hand-over-hand” movement of a kinase dimer to access E1 without dissociating from the complex.
TL;DR: It is suggested that pyruvate may accelerate its own metabolism by increasing the activity of pyruVate dehydrogenase and thus restores the cellular ATP levels in post-ischemic astrocytes.
TL;DR: Advances in understanding in human skeletal muscle of the regulatory signals and changes in gene expression which are important during acute exercise and exercise training, as well as in prolonged situations of altered nutritional status are focused on.
Abstract: During exercise in human skeletal muscle, the proportion of carbohydrate derived acetyl-CoA is determined at least in part by the activity of the PDH (pyruvate dehydrogenase) complex. Inhibition of the complex is achieved through reversible phosphorylation of the E1 subunit by a family of PDH kinase isoforms (PDK1–4) while dephosphorylation and activation of the complex is catalysed by a pair of intrinsic PDH phosphatases (PDP1 and 2). In general, the relative activity of the kinases and phosphatases is determined by a host of intramitochondrial effectors which signal energy charge, substrate and product accumulation, muscle contraction and nutritional status. This review focuses on advances in our understanding in human skeletal muscle of the regulatory signals and changes in gene expression which are important during acute exercise and exercise training, as well as in prolonged situations of altered nutritional status.
TL;DR: The results indicated that tryptophan inhibits pyruvate kinase in vitro and in vivo and that alanine prevents this inhibitory effect on the enzyme activity.
Abstract: Hypertryptophanemia is a rare inherited metabolic disorder probably caused by a blockage in the conversion of tryptophan to kynurenine, accumulating tryptophan and some of its metabolites in plasma and tissues of affected patients The patients present mild to moderate mental retardation with exaggerated affective responses, periodic mood swings, and apparent hypersexual behavior Pyruvate kinase catalyses a critical step in the glycolysis pathway, the main route that provides energy to brain functioning The main objective of the present study was to determine pyruvate kinase activity in brain cortex of rats subjected to acute chemically induced hypertryptophanemia The effect of alanine administration to the treated rats on the enzyme activity was also investigated We also studied the in vitro effect of the two amino acids on pyruvate kinase activity in the brain cortex of nontreated rats The results indicated that tryptophan inhibits pyruvate kinase in vitro and in vivo and that alanine prevents this inhibitory effect on the enzyme activity Considering the crucial role pyruvate kinase plays in glucose metabolism in brain, it is possible that inhibition of this enzyme activity may contribute to the brain damage characteristic of this disease Further studies will be necessary to evaluate possible benefits of alanine administration to the patients affected by hypertryptophanemia