Suppression of β-oxidation restores pyruvate inhibition of pyruvate dehydrogenase kinase in starved rat heart

Kinetic behaviour of rat heart pyruvate dehydrogenase kinase (PDHK) was studied in the multi-enzyme complex (PDC) contained in two preparations: mitochondria (mPDC) and a high speed pellet of Triton-extracted tissue (hPDC). Two parameters were evaluated: Va_av, related to V_max, and Fractional Pyruvate Inhibition (FPI). Starvation of rats for 48 h led to a rise in V_av and a fall in FPI. Injection into starved rats of agents which reduce -oxidation of fatty acids restored, in succession, FPI and then V_av, of hPDC, to levels found in hPDC from fed animals. In vitro incubation at 30°C of hPDC from starved animals restored FPI, but not V_av, to fed values; both were restored during in vitro incubation of mPDC from starved animals within the same time frame as in the in vivo experiments. A sharp increase of FPI, but not V_av, of hPDC from both fed and starved rats was observed in later experiments. This could have been due to differential selection of the two genes for isoenzymes of PDHKa proposed by other workers.     

The kinetics of the reversible inhibition of heart lactate dehydrogenase through the formation of the enzyme–oxidized nicotinamide–adenine dinucleotide–pyruvate compound

The inhibition of lactate dehydrogenase at high pyruvate concentration was studied in three ways. First, a rapid decrease in the rate of the enzyme reaction was observed; secondly, the rate of formation of a pyruvate-NAD(+) compound was followed by the change in E(325); thirdly, the rate of quenching of the protein fluorescence was measured. The data obtained at pH6.0 at different temperatures and ionic strengths as functions of pyruvate, NAD(+) and enzyme concentrations show that the extent of inhibition can be correlated with the reversible formation of a compound between pyruvate and enzyme-bound NAD(+). It is suggested that the detailed kinetic analysis of the formation of this abortive ternary compound will give pertinent information about properties of the enzyme-NAD(+) compound involved in the normal catalytic process.     

Crystallization and characterization of human liver kynurenine–glyoxylate aminotransferase. Identity with alanine–glyoxylate aminotransferase and serine–pyruvate aminotransferase

Kynurenine–glyoxylate aminotransferase, alanine–glyoxylate aminotransferase and serine–pyruvate aminotransferase were co-purified and crystallized as yellow cubes from human liver particulate fraction. The crystalline enzyme was homogeneous by the criteria of electrophoresis, isoelectric focusing, gel filtration, sucrose-density-gradient centrifugation and analytical ultracentrifugation. The molecular weight of the enzyme was calculated as approx. 90000, 89000 and 99000 by the use of gel filtration, analytical ultracentrifugation and sucrose-density-gradient centrifugation respectively, with two identical subunits. The enzyme has a s_20,w value of 5.23S, an isoelectric point of 8.3 and a pH optimum between 9.0 and 9.5. The enzyme solution showed absorption maxima at 280 and 420nm. The enzyme catalysed transamination between several l-amino acids and pyruvate or glyoxylate. The order of effectiveness of amino acids was alanine>serine>glutamine>glutamate>methionine>kynurenine = phenylalanine = asparagine>valine>histidine>lysine>leucine>isoleucine>arginine>tyrosine = threonine>aspartate, with glyoxylate as amino acceptor. The enzyme was active with glyoxylate, oxaloacetate, hydroxypyruvate, pyruvate, 4-methylthio-2-oxobutyrate and 2-oxobutyrate, but showed little activity with phenylpyruvate, 2-oxoglutarate and 2-oxoadipate, with kynurenine as amino donor. Kynurenine–glyoxylate aminotransferase activity was competitively inhibited by the addition of l-alanine or l-serine. From these results we conclude that kynurenine–glyoxylate aminotransferase, alanine–glyoxylate aminotransferase and serine–pyruvate aminotransferase activities of human liver are catalysed by a single protein. Kinetic parameters for the kynurenine–glyoxylate aminotransferase, alanine–glyoxylate aminotransferase, serine–pyruvate aminotransferase and alanine–hydroxypyruvate aminotransferase reactions of the enzyme are presented.     

Evaluation of α-hydroxycinnamic acids as pyruvate carboxylase inhibitors

Through a structure-based drug design project (SBDD), potent small molecule inhibitors of pyruvate carboxylase (PC) have been discovered. A series of α-keto acids (7) and α-hydroxycinnamic acids (8) were prepared and evaluated for inhibition of PC in two assays. The two most potent inhibitors were 3,3′-(1,4-phenylene)bis[2-hydroxy-2-propenoic acid] (8u) and 2-hydroxy-3-(quinoline-2-yl)propenoic acid (8v) with IC₅₀ values of 3.0 ± 1.0 μM and 4.3 ± 1.5 μM respectively. Compound 8v is a competitive inhibitor with respect to pyruvate (K_i = 0.74 μM) and a mixed-type inhibitor with respect to ATP, indicating that it targets the unique carboxyltransferase (CT) domain of PC. Furthermore, compound 8v does not significantly inhibit human carbonic anhydrase II, matrix metalloproteinase-2, malate dehydrogenase or lactate dehydrogenase.     

Ethyl pyruvate inhibits proliferation and induces apoptosis of hepatocellular carcinoma via regulation of the HMGB1–RAGE and AKT pathways

Ethyl pyruvate (EP) was recently identified as a stable lipophilic derivative of pyruvic acid with significant antineoplastic activities. The high mobility group box-B1 (HMGB1)–receptor for advanced glycation end-products (RAGE) and the protein kinase B (Akt) pathways play a crucial role in tumorigenesis and development of many malignant tumors. We tried to observe the effects of ethyl pyruvate on liver cancer growth and explored its effects in hepatocellular carcinoma model. In this study, three hepatocellular carcinoma cell lines were treated with ethyl pyruvate. An MTT colorimetric assay was used to assess the effects of EP on cell proliferation. Flow cytometry and TUNEL assays were used to analyze apoptosis. Real-time PCR, Western blotting and immunofluorescence demonstrated ethyl pyruvate reduced the HMGB1–RAGE and AKT pathways. The results of hepatoma orthotopic tumor model verified the antitumor effects of ethyl pyruvate in vivo. EP could induce apoptosis and slow the growth of liver cancer. Moreover, EP decreased the expression of HMGB1, RAGE, p-AKT and matrix metallopeptidase-9 (MMP9) and increased the Bax/Bcl-2 ratio. In conclusion, this study demonstrates that ethyl pyruvate induces apoptosis and cell-cycle arrest in G phase in hepatocellular carcinoma cells, plays a critical role in the treatment of cancer.     

Efficient production of α-acetolactate by whole cell catalytic transformation of fermentation-derived pyruvate

With a variety of physiological and pharmacological functions, menaquinone is an essential prenylated product that can be endogenously converted from phylloquinone (VK1) or menadione (VK3) via the expression of Homo sapiens UBIAD1 (HsUBIAD1). The methylotrophic yeast, Pichia pastoris, is an attractive expression system that has been successfully applied to the efficient expression of heterologous proteins. However, the menaquinone biosynthetic pathway has not been discovered in P. pastoris. Firstly, we constructed a novel synthetic pathway in P. pastoris for the production of menaquinone-4 (MK-4) via heterologous expression of HsUBIAD1. Then, the glyceraldehyde-3-phosphate dehydrogenase constitutive promoter (PGAP) appeared to be mostsuitable for the expression of HsUBIAD1 for various reasons. By optimizing the expression conditions of HsUBIAD1, its yield increased by 4.37 times after incubation at pH 7.0 and 24 °C for 36 h, when compared with that under the initial conditions. We found HsUBIAD1 expressed in recombinant GGU-23 has the ability to catalyze the biosynthesis of MK-4 when using VK1 and VK3 as the isopentenyl acceptor. In addition, we constructed a ribosomal DNA (rDNA)-mediated multi-copy expression vector for the fusion expression of SaGGPPS and PpIDI, and the recombinant GGU-GrIG afforded higher MK-4 production, so that it was selected as the high-yield strain. Finally, the yield of MK-4 was maximized at 0.24 mg/g DCW by improving the GGPP supply when VK3 was the isopentenyl acceptor. In this study, we constructed a novel synthetic pathway in P. pastoris for the biosynthesis of the high value-added prenylated product MK-4 through heterologous expression of HsUBIAD1 and strengthened accumulation of GGPP. This approach could be further developed and accomplished for the biosynthesis of other prenylated products, which has great significance for theoretical research and industrial application.     

Optimization and structure–activity relationships of a series of potent inhibitors of methicillin-resistant Staphylococcus aureus (MRSA) pyruvate kinase as novel antimicrobial agents

A novel series of hydrazones were synthesized and evaluated as inhibitors of methicillin-resistant Staphylococcus aureus (MRSA) pyruvate kinase (PK). PK has been identified as one of the most highly connected ‘hub proteins’ in MRSA. PK has been shown to be critical for bacterial survival which makes it a potential target for development of novel antibiotics and the high degree of connectivity implies it should be very sensitive to mutations and thus less able to develop resistance. PK is not unique to bacteria and thus a critical requirement for such a PK inhibitor would be that it does not inhibit the homologous human enzyme(s) at therapeutic concentrations. Several MRSA PK inhibitors (including 8d) were identified using in silico screening combined with enzyme assays and were found to be selective for bacterial enzyme compared to four human PK isoforms (M1, M2, R and L). However these lead compounds did not show significant inhibitory activity for MRSA growth presumably due to poor bacterial cell penetration. Structure–activity relationship (SAR) studies were carried out on 8d and led us to discover more potent compounds with enzyme inhibiting activities in the low nanomolar range and some were found to effectively inhibit bacteria growth in culture with minimum inhibitory concentrations (MIC) as low as 1 μg/mL. These inhibitors bind in two elongated flat clefts found at the minor interfaces in the homo-tetrameric enzyme complex and the observed SAR is in keeping with the size and electronic constraints of these binding sites. Access to the corresponding sites in the human enzyme is blocked.     

The correlation between glycogen–glycolysis metabolite pyruvate and vancomycin antibiotic productions of Amycolatopsis orientalis grown in glucose medium

The effect of glucose concentration in the growth medium on the relationship between glycolysis, glycogen accumulation and vancomycin production of Amycolatopsis orientalis was investigated depending on the incubation time. After a lag phase, bacterial growth of A. orientalis began and biomass concentration increased continuously up to 36th or 48th hours while glucose concentration in the culture medium was consumed rapidly in the same time of incubation. In addition, increase in glucose concentrations of the growth medium lead to increase intracellular glucose as well as glycerol levels. Intracellular pyruvate levels increased significantly up to 15 g/L while extracellular pyruvate levels with respect to increases in glucose concentration. A positive correlation between glucose kinase activities and glucose concentration was determined during the incubation period. Pyruvate kinase activity increased up to 15 g/L glucose and 48th hour of incubation. As a glycopeptide antibiotic, vancomycin production increased with the increases in glucose concentrations up to 15 g/L. These results indicated that glycogen accumulation with respect to glucose concentration of the growth medium was concomitant with the sporulation of A. orientalis. When the initial glucose concentration exceeded 15 g/L, pyruvate excretions as well as intracellular glycogen and glycerol productions were supported in spite of repression in vancomycin production of A. orientalis.     

Formation of β-cyanoalanine and pyruvate by Acacia georginae

Pyruvate is formed on incubation of l-cysteine with acetone powder preparations of Acacia georginae but in the presence of cyanide, β-cyanoalanine is produced and pyruvate production is highly depressed. The pH optimum for pyruvate production is 8·5. In the presence of fluoride (1·5 mM), the pH profile is unchanged and in the presence of cyanide (1·5 mM), minimal pyruvate production occurs at pH 8·5. Although addition of pyridoxal phosphate had no influence on pyruvate or β-Cyanoalanine production, these processes were prevented by sodium borohydride, an inhibitor of pyridoxal enzymes. Neither l-serine nor O-acetyl-l-serine serve as alternative substrates for pyruvate production. β-Fluoroalanine was not detected on incubating fluoride with an enzyme preparation from A. georginae acetone powders.     

“Stable” effects of insulin and isoproterenol on adipocyte pyruvate dehydrogenase

Insulin, at a concentration of 1 mU/ml, stimulated glycogen synthase and pyruvate dehydrogenase about threefold in isolated rat adipocytes. Upon the removal of insulin, glycogen synthase activity remained in the activated state for 10 min and thereafter rapidly returned to basal level. On the other hand, insulin-stimulated pyruvate dehydrogenase activity remained elevated for at least 30 min. Isoproterenol (10⁻⁸m) stimulated phosphorylase and inhibited pyruvate dehydrogenase through the activation of β-adrenergic receptors. Addition of the β-antagonist, propranolol (10⁻⁵m), after isoproterenol reversed the action of isoproterenol on phosphorylase but not its action on pyruvate dehydrogenase. Dibutyryl cyclic AMP, when added to intact adipocytes, produced an effect on pyruvate dehydrogenase similar to that induced by isoproterenol. Our results indicate that both insulin and the β-agonist have a unique action on pyruvate dehydrogenase which is different from their effects on other enzymes such as glycogen synthase and phosphorylase.     

Increased liver l-serine–pyruvate aminotransferase activity under gluconeogenic conditions (Short Communication)

Rat liver l-serine-pyruvate aminotransferase activity exceeds markedly the normal adult value (a) in the neonatal period, (b) after glucagon injection and (c) after alloxan injection, observations that reinforce the suggestion from comparative findings that the aminotransferase has a role in gluconeogenesis. Some findings, however, argue in favour of l-serine dehydratase as the enzyme of gluconeogenesis from l-serine.     

Separation and purification of α-ketoglutarate and pyruvate from the fermentation broth of Yarrowia lipolytica

Bioprocess and Biosystems Engineering - A strategy to achieve the efficient co-production of α-ketoglutarate (KGA) and pyruvate (PYR) via Yarrowia lipolytica fermentation was established in...     

Effects of antisense repression of an Arabidopsis thaliana pyruvate dehydrogenase kinase cDNA on plant development⋆

Pyruvate dehydrogenase kinase (PDHK), a negative regulator of the mitochondrial pyruvate dehydrogenase (PDH) complex (mtPDC), plays a pivotal role in controlling mtPDC activity, and hence, the TCA cycle and cell respiration. This report describes the cloning of a pyruvate dehydrogenase kinase cDNA (AtPDHK) from Arabidopsis thaliana and focuses on the effects of antisense down-regulation of its expression on plant growth and development. The deduced amino acid sequence of AtPDHK exhibits extensive similarity to other plant and mammalian PDHKs, containing conserved domains typical of two-component histidine protein kinases. The Escherichia coli expressed AtPDHK specifically phosphorylated mammalian PDH E1 in a time-dependent manner. Antisense expression of the AtPDHK cDNA led to marked elevation of mtPDC activity in transgenic plants with increases ranging from 137% to 330% compared to control plants. Immunoblot analyses performed with a monoclonal antibody to the E1 mtPDH component (the subunit phosphorylated by PDHK) indicated that the increased mtPDC activity was not the result of an increase in the level of PDH protein. MtPDC from transgenic plants showed a reduced sensitivity to ATP-dependent inactivation compared to that observed in wild-type plants. Collectively, these data suggest that the antisense partial silencing of the negative regulator, PDHK, was responsible for the increased mtPDC activity observed in the antisense PDHK plants. Transgenic plants with partially repressed AtPDHK also displayed altered vegetative growth with reduced accumulation of vegetative tissues, early flower development and shorter generation time. The potential role for AtPDHK gene manipulation in crop improvement is discussed.     

Enzymatic synthesis of l-norephedrine by coupling recombinant pyruvate decarboxylase and ω-transaminase

l-Norephedrine, a natural plant alkaloid, possesses similar activity as ephedrine and can be used as a vicinal amino alcohol for the asymmetric synthesis of a variety of optically pure compounds, including pharmaceuticals, fine chemicals, and agrochemicals. Because of the existence of two asymmetric centers, efficient synthesis of l-norephedrine has been challenging. In the present study, an R-selective pyruvate decarboxylase from Saccharomyces cerevisiae and an S-selective ω-transaminase from Vibrio fluvialis JS17 were coupled to develop a sequential process for the stereoselective biosynthesis of l-norephedrine. After systematic optimization of the reaction conditions, a green, economic, and practical biocatalytic method to prepare l-norephedrine was established to achieve de and ee values of greater than 99.5 % and a molar yield over 60 %. The present coupling approach can facilitate the development of sequential reactions by various biocatalysts.     

Antitumor activity of SR splicing-factor 5 knockdown by downregulating pyruvate kinase M2 in non–small cell lung cancer cells

SR splicing-factors (SRSFs) play a vital role in carcinogenesis. SRSF5 was demonstrated to be upregulated in lung cancer and identified as a novel prognostic indicator for small-cell lung cancer. However, the role of SRSF5 in the pathogenesis of non–small cell lung cancer (NSCLC) and the molecular mechanism involved are still undefined. The expression of SRSF5 in NSCLC cells was detected by quantitative real-time polymerase chain reaction and Western blot analysis. The proliferation of cells was evaluated by cell counting kit-8 and BrdU assays. Apoptosis was assessed by flow cytometry and Western blot analysis of apoptosis-associated proteins including B-cell lymphoma 2 (Bcl-2), Bax, and cytochrome C (Cyt C). Glycolysis was detected by determining glucose consumption, lactate production, and pyruvate kinase M2 (PKM2) expression. We found that SRSF5 messenger RNA and protein levels were elevated in NSCLC cells. SRSF5 knockdown inhibited the proliferation and Ki67 expression in NSCLC cells. SRSF5 silencing increased the apoptotic rate, upregulated Bax and Cyt C, and decreased Bcl-2 level in NSCLC cells. Moreover, Knockdown of SRSF5 repressed glycolysis in NSCLC cells via reducing PKM2 expression. Enhanced glycolysis by PKM2 overexpression attenuated the effects of SRSF5 silencing on NSCLC cell proliferation and apoptosis. Overall, knockdown of SRSF5 inhibited proliferative ability and induced apoptosis by suppressing PKM2 expression in NSCLC cells.     

Cotranslation of L and L′ pyruvate kinase messenger RNAs from human fetal liver

Human fetal liver RNA translated in a rabbit reticulocyte cell-free system directed synthesis of two polypeptides which could be identified by immunological competition as L and L′ pyruvate kinase subunits. Messenger RNAs specifying synthesis of both types of subunits exhibited a sedimentation coefficient of 21–22 S.     

Effects of propionate on accumulation of poly(β-hydroxy-butyrate-co-β-hydroxyvalerate) and excretion of pyruvate in Alcaligenes eutrophus

Summary Effects of propionate on the accumulation of poly(-hydroxybutyrate-co--hydroxyvalerate) and the excretion of pyruvate in Alcaligenes eutrophus were investigated at various concentrations of glucose and propionate. As propionate concentration increased, an enhancement in pyruvate excretion was observed along with a decrease in the yield of the copolymer. At the same concentration of propionate, hydroxyvalerate content of the copolymer was reduced from 26 to 15 mol % with increase of the initial glucose concentration.