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PubMed1984

Fatty liver caused by chronic alcohol ingestion is prevented by dietary supplementation with pyruvate or glycerol.

Earlier studies showed that the fatty liver, caused by feeding rats the Lieber-DeCarli alcohol diet for four weeks, was prevented if the diet was supplemented with dihydroxyacetone (22 g/l), pyruvate (22 g/l) and riboflavin (2.2 g/l). In the present study, we observed that fatty liver was prevented if the alcohol diet was supplemented with glycerol and lactate (22 g/l each) and riboflavin (2.2 g/l). Hence, the prevention of alcoholic fatty liver by the dietary supplementation with dihydroxyacetone and pyruvate may not be related to their capacity to serve as hydrogen acceptors and to oxidize NADH produced during ethanol metabolism. When rats were fed the alcohol diet supplemented with either glycerol or pyruvate, the hepatic triglyceride (TG) levels were similar to those in rats pair-fed a Lieber-DeCarli control diet in which alcohol was replaced with an isocaloric amount of dextrins. Therefore, the prevention of fatty liver does not require the simultaneous presence of several supplements. Dietary dihydroxyacetone or riboflavin did not reduce alcoholic fatty liver. Supplementation of the ethanol diet with isocaloric amounts of lactate or glucose, instead of pyruvate, did not abolish the development of fatty liver but caused a marked reduction in the hepatic TG levels. Animals fed the alcohol diet consumed only small amounts of carbohydrate for long periods of time. Since the inclusion of glucose or its metabolites in the alcohol diet fed to rats caused a marked decrease in the liver TG content, it is likely that the production or prevention of fatty liver is related to carbohydrate metabolism.

Animals↗

PubMed1989

Positron emission tomography using pyruvate-1-11C in two cases of mitochondrial encephalomyopathy.

Positron emission tomography (PET) using pyruvate-1-11C was carried out to investigate the in vivo metabolism of pyruvate in the brains of patients with mitochondrial encephalomyopathy and Leigh's disease. Two epileptic patients were studied as control subjects. Radioactivity was eliminated from the brain tissue of the epileptic patients soon after injection of pyruvate-1-11C. PET images of mitochondrial encephalomyopathy patients showed an increase in radioactivity in the cerebral cortex, basal ganglia and thalamus, with elimination of radioactivity being slower than that of epileptic patients. One patient with Leigh's disease showed similar PET images. PET using pyruvate-1-11C is useful for the evaluation of mitochondrial energy metabolism in the brain.

Brain Diseases↗

PubMed2001

Redirection of pyruvate catabolism in Lactococcus lactis by selection of mutants with additional growth requirements.

Based on requirements for acetate or lipoic acid for aerobic (but not anaerobic) growth, Lactococcus lactis subsp. lactis mutants with impaired pyruvate catabolism were isolated following classical mutagenesis. Strains with defects in one or two of the enzymes, pyruvate formate-lyase (PFL), lactate dehydrogenase (LDH) and the pyruvate dehydrogenase complex (PDHC) were obtained. Growth and product formation of these strains were characterized. A PFL-defective strain (requiring acetate for anaerobic growth) displayed a two-fold increase in specific lactate production compared with the corresponding wild-type strain when grown anaerobically. LDH defective strains directed 91-96% of the pyruvate towards alpha-acetolactate, acetoin and diacetyl production when grown aerobically in the presence of acetate and absence of lipoic acid (a similar characteristic was observed in an LDH and PDHC defective strain in the presence of both acetate and lipoic acid) and more than 65% towards formate, acetate and ethanol production under anaerobic conditions. Another strain with defective PFL and LDH was strictly aerobic. However, a variant with strongly enhanced diacetyl reductase activities (NADH/NAD+ dependent diacetyl reductase, acetoin reductase and butanediol dehydrogenase activities) was selected from this strain under anaerobic conditions by supplementing the medium with acetoin. This strain is strictly aerobic, unless supplied with acetoin.

Acetyltransferases↗

PubMed2000

Import, processing, and assembly of the alpha- and beta-subunits of chloroplast pyruvate dehydrogenase.

Sequence comparisons were used to identify cDNAs potentially encoding the alpha- and beta-subunits of chloroplast pyruvate dehydrogenase. Coupled in-vitro transcription plus translation was used to synthesize radiolabeled pyruvate dehydrogenase alpha- and beta-subunit precursor proteins. When the precursors were incubated with intact pea (Pisum sativum L.) seedling chloroplasts in the presence of ATP, they were imported and proteolytically processed. In contrast, there was no import or processing of the precursors by isolated, intact pea seedling mitochondria. Monospecific antibodies to the recombinant pyruvate dehydrogenase alpha-subunit were additionally able to co-precipitate radiolabeled pyruvate dehydrogenase beta-subunit, indicating association between subunits after import and processing. Furthermore, size-exclusion chromatography was used to identify an alphabeta heterodimer that is an intermediate in the assembly of the native alpha2beta2 heterotetrameric enzyme.

Chloroplasts↗

PubMed1984

Nonenzymatic decarboxylation of pyruvate.

Triton X-100, retinol, retinoic acid, retinal, hexane, dithiothreitol, mercaptoethanol, and some other commercially available chemicals caused nonenzymatic decarboxylation of pyruvate and alpha-ketoglutarate. "Lipids" obtained from human or pigeon liver homogenates using isopropanol/hexane also had very high nonenzymatic decarboxylating activity on these two alpha-ketoacids; most of this activity could be traced to the hexane (Eastman) used in the extraction. Optimum pH of the reaction with dithiothreitol and mercaptoethanol was 7-8 and with the other chemicals around 10, but considerable activity was present at pH 7-8. Liver homogenates had a scavenger effect on the decarboxylating activity of Triton X-100 and of dithiothreitol. Dithiothreitol and mercaptoethanol at high concentrations (greater than 1 mM) also had a scavenger effect on the decarboxylating activity of the "lipids." Pretreatment of Triton X-100, dithiothreitol, retinol, and the "lipids" with catalase markedly decreased the decarboxylating activity, while treatment with boiled catalase failed to do so. The results suggest that these compounds contain oxidizing contaminants, perhaps peroxide derivatives. Powerful oxidizing impurities have been reported in Triton X-100 from various sources by Y. Ashani and G. N. Catravas (1980, Anal. Biochem 109, 55-62). Such peroxide derivatives may cause nonenzymatic decarboxylation of pyruvate and alpha-ketoglutarate, presumably by a mechanism similar to the well-known nonenzymatic decarboxylation of alpha-ketoacids by hydrogen peroxide. In the absence of catalase and/or other protective agents against reactive oxygen derivatives, these chemicals would interfere in the assays of pyruvate dehydrogenase, pyruvate dehydrogenase complex, and alpha-ketoglutarate dehydrogenase complex which depend on the release of 14CO2 from alpha[1-14C]ketoacids.

Animals↗

PubMed1984

Interaction of alpha-cyano[14C]cinnamate with the mitochondrial pyruvate translocator.

The binding of alpha-cyanocinnamate to rat-heart mitochondrial membrane was investigated using alpha-cyano[14C]cinnamate. The binding was correlated to the inhibition of pyruvate transport. The results obtained demonstrate that both these functions reach saturation at the same titre of the inhibitor. Quantitative parameters of alpha-cyano[14C]cinnamate binding have been determined. The binding can be prevented by pyruvate and other substrates of the carrier but not by acetate. Pyruvate decreases the affinity of alpha-cyanocinnamate binding, leaving the maximum number of binding unchanged. It is concluded that rat-heart mitochondria contain a specific site at which alpha-cyanocinnamate binds which is directly involved in the inhibition of pyruvate transport.

Animals↗

PubMed1995

Hypothyroid state and membrane fatty acid composition influence cardiac mitochondrial pyruvate oxidation.

Pyruvate oxidation was measured in cardiac mitochondria from euthyroid and hypothyroid rats fed diets enriched with either omega-6 or omega-3 fatty acids. Both State 4 and State 3 rates of pyruvate-dependent respiration were markedly reduced in hypothyroid mitochondria, regardless of diet consumed, compared to euthyroid controls. Respiratory control ratios and ADP/O ratios were the same under all treatments. While there was no significant effect of diet on respiration in euthyroid mitochondria, pyruvate oxidation was 28% higher in hypothyroid mitochondria from animals fed the omega-3 diet compared to those fed the omega-6 diet. Depressed respiration in the hypothyroid state was correlated with 18% more phosphatidylcholine in the inner mitochondrial membrane whereas phosphatidylethanolamine was 17% lower and cardiolipin 32% lower compared to controls. The total phospholipid fatty acid composition was not affected by the hypothyroid state. However, enhanced respiration in hypothyroid animals fed the omega-3 diet was associated with a 3-fold increase in monounsaturated fatty acids in the cardiolipin fraction, and a 12-fold increase in omega-3 fatty acids, primarily 22:5(omega-3) and 22:6(omega-3). The data suggest that membrane levels of cardiolipin and its omega-3 fatty acid content modulate pyruvate transport in hypothyroid mitochondria.

Animals↗

PubMed1978

Use of methanethiolation to investigate the catalytic role of sulphydryl groups in rabbit skeletal muscle pyruvate kinase.

Incubation of rabbit skeletal muscle pyruvate kinase (ATP:pyruvate 2-O-phosphotransferase, EC 2.7.1.40) with methyl methanethiosulphonate resulted in the time- and inhibitor concentration-dependent loss of enzyme activity. Substrates or products of the catalytic reaction prevented the loss of activity caused by methanethiolation. Their effectiveness as protecting agents was placed in the order ADP greater than ATP greater than Mg2+ greater than phosphoenolpyruvate greater than pyruvate. The essential catalytic cation, K+, had no effect on the methanethiolation reaction. [Me-3H]Methanethiosulphonate modified all the available cysteine thiol groups which correlated to the incorporation of four SC3H3 groups per protomer. Four radioactive peptides were obtained on tryptic peptide mapping. When methanethiolation was carried out in the presence of Mg2+ alone or with Mg2+ and ATP together, then only three SC3H3 groups were incorporated into each subunit. If MgATP protected methanethiolated pyruvate kinase was reacted with iodo[2-3H]acetic acid then 1.37 +/- 0.2 groups per protomer were carboxymethylated. 70% of the radioactivity was located in a single peptide on tryptic peptide mapping. This peptide was isolated and contained the segment carboxymethyl cysteine (Glx, Asx, Ser) Arg. Collectively these data indicate that although all thiol groups are equally accessible to methyl methanethiosulphonate, only a single thiol group participates in the catalytic event. An additional role in the maintenance of structure for this thiol group was also shown in studied of reduction and thermal denaturation of the enzyme.

Adenosine Diphosphate↗

PubMed1979

Purification and properties of the Ascaris pyruvate dehydrogenase complex.

The pyruvate dehyhdrogenase complex (pyruvate:lipoate oxidoreductase (decarboxylating and acceptor-acetylating), EC 1.2.4.1) has been isolated from Ascaris muscle mitochondria and purified to near homogeneity by differential centrifugation, (NH4)2SO4 fractionation and calcium phosphate gel-cellulose chromatography. It is similar in shape, size and physical characteristics to pyruvate dehydrogenase complexes isolated from mammalian sources. It has an absolute dependence on CoA, NAD+ and pyruvate for activity and is competitively inhibited by acetyl-CoA and NADH. However, much higher NADH/NAD+ ratios are necessary to inhibit activity, suggesting regulation by the more reduced state of the pyridine nucleotide pool in Ascaris mitochondria.

Acetyl Coenzyme A↗

PubMed1985

Inhibition of 2-oxoglutarate oxidation in plant mitochondria by pyruvate.

Oxidation of 2-oxoglutarate (in the presence of malonate) by mitochondria isolated from turnip, pea leaf and cauliflower tissue was dramatically inhibited by micromolar concentrations of pyruvate. Pyruvate, however, had little or no effect on 2-OG oxidation when carried out in the absence of malonate. The inhibition was reversed by alpha-cyano-4-hydroxycinnamic acid, indicating pyruvate uptake into the matrix was required for the inhibitory effect. In contrast, pyruvate had no effect on 2-oxoglutarate oxidation by mitochondria isolated from rat heart. The possible significance of the effect in terms of the control of 2-oxoglutarate dehydrogenase activity during the operation of a malate/aspartate shuttle in plant mitochondria is discussed.

Animals↗

PubMed1982

Inhibition by valproic acid of pyruvate uptake by brain mitochondria.

The anticonvulsive drug, valproic acid, inhibits competitively the pyruvate carrier in rat brain and liver mitochondria. Due to this inhibition the oxygen consumption supported by pyruvate oxidation is also affected. In our experimental conditions, pyruvate oxidation is partially inhibited by VPA concentration as low as 0.05 mM. Valproic acid, however, is unable, even at 10 mM, to fully inhibit pyruvate oxidation. Concentrations of VPA higher than 1 mM have an uncoupling effect on mitochondrial respiration. The oxidation of other mitochondrial substrates such as isocitrate, 2-ketoglutarate, DL-3-hydroxybutyrate and succinate is uncoupled but not inhibited by VPA. The effects of VPA on mitochondrial metabolism may be related to the therapeutic and/or toxicologic properties of this drug.

Animals↗

PubMed1994

Regulation of alternative oxidase kinetics by pyruvate and intermolecular disulfide bond redox status in soybean seedling mitochondria.

Two factors known to regulate plant mitochondrial cyanide-resistant alternative oxidase activity, pyruvate and the redox status of the enzyme's intermolecular disulfide bond, were shown to differently affect activity in isolated soybean seedling mitochondria. Pyruvate stimulated alternative oxidase activity at low levels of reduced ubiquinone, shifting the threshold level of ubiquinone reduction for enzyme activity to a lower value. The disulfide bond redox status determined the maximum enzyme activity obtainable in the presence of pyruvate, with the highest rates occurring when the bond was reduced. With variations in cellular pyruvate levels and in the proportion of reduced alternative oxidase protein, a wide range of enzyme activity is possible in vivo.

Disulfides↗

PubMed1996

Chemical modification of the essential arginine residues of pyruvate dehydrogenase prevents its phosphorylation by kinase.

The mechanism of regulatory phosphorylation of the pyruvate dehydrogenase component (E1) of muscle pyruvate dehydrogenase complex was studied. Chemical modification of the arginine residues essential for substrate binding was shown to prevent incorporation of 32P from [gamma-32P]ATP into E1 catalyzed by kinase and to exclude completely the interaction of holo-E1 with pyruvate. It is proposed that negatively charged phosphoseryl residues may compete with pyruvate for the active site arginine and thereby block the substrate binding.

Animals↗

PubMed1991

Hexose metabolism in pancreatic islets. Regulation of aerobic glycolysis and pyruvate decarboxylation.

1. D-Glucose (0.5-16.7 mM) preferentially stimulates aerobic glycolysis and D-[3,4-14C]glucose oxidation, relative to D-[5-3H]glucose utilization in rat pancreatic islets, the concentration dependency of such a preferential effect displaying a sigmoidal pattern. 2. Inorganic and organic calcium antagonists, as well as Ca2+ deprivation, only cause a minor decrease in the ratio between D-[3,4-14C]glucose oxidation and D-[5-3H]glucose utilization in islets exposed to a high concentration of the hexose (16.7 mM). 3. Non-glucidic nutrient secretagogues such as 2-aminobicyclo[2,2,1]heptane-2-carboxylate (BCH), 2-ketoisocaproate and 3-phenylpyruvate fail to stimulate aerobic glycolysis and D-[3,4-14C]glucose oxidation in islets exposed to 6.0 mM D-glucose. Nevertheless, BCH augments [1-14C]pyruvate and [2-14C]pyruvate oxidation. 4. The glucose-induced increment in the paired ratio between D-[3,4-14C]glucose oxidation and D-[5-3H]glucose utilization is impaired in the presence of either cycloheximide or ouabain. 5. These findings suggest that the preferential effect of D-glucose upon aerobic glycolysis and pyruvate decarboxylation is not attributable solely to a Ca(2+)-induced activation of FAD-linked glycerophosphate dehydrogenase and/or pyruvate dehydrogenase, but may also involve an ATP-modulated regulatory process.

Aerobiosis↗

PubMed1992

Beta-oxidation as channeled reaction linked to citric acid cycle: evidence from measurements of mitochondrial pyruvate oxidation during fatty acid degradation.

1. The kinetics of mitochondrial mammalian pyruvate dehydrogenase multienzyme complex (PDHC) is studied by the formation of CO2 using tracer amounts of [1-14C]pyruvate. It is found that the Hill plot results in a (pseudo-)cooperativity with a transition of n-1----3 at a pyruvate concentration about Ks. 2. Addition of L-carnitine, octanoate, palmitoyl-CoA or palmitate + L-carnitine + fatty acid-binding protein results in a Hill coefficient of n = 2 following the kinetics of pyruvate oxidation. 3. Addition of fatty acid-binding protein to an assay system oxidizing palmitate in presence of L-carnitine alters the pattern of the kinetics in the Hill plot so that an apparently lower level of L-carnitine is necessary for the reaction course of beta-degradation. 4. It is concluded that beta-degradation is a coordinated, multienzyme-complex based mechanism tightly linked to citric acid cycle and it is proposed that L-carnitine is actively involved into the reaction and not only functioning as carrier-molecule for transmembrane transport.

Animals↗

PubMed1996

Effects of pyruvate and lactate on food intake in rat strains sensitive and resistant to dietary obesity.

We have investigated the effects of peripherally administered pyruvate and lactate on the intake of high fat (HF) and low fat (LF) diets by a strain of rat either sensitive (Osborne-Mendel, OM) or resistant (SSB/Pl) to high fat-induced obesity. Both pyruvate and lactate inhibited the intake of HF and LF diets by OM rats and these effects were blocked by selective hepatic vagotomy. In contrast, in S5B/Pl rats fed an LF diet the responses to pyruvate and lactate were attenuated and were absent in S5B/Pl rats fed the HF diet. These data suggest that OM and S5B/Pl rats differ either in their metabolism of pyruvate and lactate or in their responses to these metabolites.

Animals↗

PubMed1990

The in vitro effects of four isomers of dinitrotoluene on rat Sertoli and Sertoli-germ cell cocultures: germ cell detachment and lactate and pyruvate production.

The present study was undertaken to evaluate the in vitro effects of four isomers of a known testicular toxicant, dinitroluene (DNT). Rat Sertoli or Sertoli-germ cell cocultures were treated, after 3 days in culture, with DNT isomers (0.01 to 100 microM) or 1,3-dinitrobenzene (1,3-DNB) for 24 hr. Cellular morphology, germ cell detachment (GCD) and lactate pyruvate production were used as sensitive effect markers of in vitro toxicity. Morphologically the Sertoli cell monolayer remained intact 24 hr after exposure to DMSO, 1,3-DNB, or DNT isomers. Some apparent cytotoxicity was observed at 100 microM 3,4-DNT: the monolayer was disrupted with extensive vacuolation of the Sertoli cells. Cocultures treated with concentrations of 50 microM DNT isomers closely resembled cells treated with 100 microM 1,3-DNB. GCD increased in a dose-dependent manner (0.01 and 10 microM DNT isomers) increasing between 2- and 10-fold over control. Both lactate and pyruvate production increased with rising concentrations of DNT isomers. The most sensitive effect was seen with 3,4-DNT (10 to 25 microM). In the case of 2,6-DNT, despite increases in GCD and lactate production, only a minimal increase in pyruvate was demonstrated. Overall, the ratio of lactate to pyruvate production declined with increasing doses of DNT. These results indicate that the four isomers of DNT directly affected Sertoli cell morphology and function, effects comparable to those seen with the Sertoli cell toxicant 1,3-DNB. Further, the data support the hypothesis that DNT may be a Sertoli cell toxicant.

Animals↗

PubMed1984

An enzyme specific method for estimation of pyruvic acid radioactivity in biological samples.

A method for the estimation of pyruvate radioactivity in complex biological samples is presented. After perchloric acid deproteinization, the samples were divided in two aliquots. All pyruvate was removed from the first aliquot with lactate dehydrogenase and NADH; the other was left undisturbed. Then all hydrophilic components of the sample were removed through an Amberlite XAD-7 column. The samples were treated with dinitrophenylhydrazine to obtain the corresponding hydrazones, which were retained in an Amberlite XAD-7 column and then were eluted with acetone and their radioactivity counted. The difference between both aliquots corresponded to the pyruvate radioactivity in the sample. No contamination by lactate, glycerol, glucose or amino acids was observed. The mean recovery of 5 determinations of pyruvate radioactivity was 91.3% +/- 1.0.

Acrylic Resins↗