Showing papers on "Pyruvate dehydrogenase kinase published in 1976"
TL;DR: This paper showed that pyruvate dehydrogenase in perfused rat heart was decreased by alloxan-diabetes or by perfusion with media containing acetate, n-octanoate or palmitate.
Abstract: The proportion of active (dephosphorylated) pyruvate dehydrogenase in perfused rat heart was decreased by alloxan-diabetes or by perfusion with media containing acetate, n-octanoate or palmitate. The total activity of the dehydrogenase was unchanged. 2. Pyruvate (5 or 25mM) or dichloroacetate (1mM) increased the proportion of active (dephosphorylated) pyruvate dehydrogenase in perfused rat heart, presumably by inhibiting the pyruvate dehydrogenase kinase reaction. Alloxan-diabetes markedly decreased the proportion of active dehydrogenase in hearts perfused with pyruvate or dichloroacetate. 3. The total activity of pyruvate dehydrogenase in mitochondria prepared from rat heart was unchanged by diabetes. Incubation of mitochondria with 2-oxo-glutarate plus malate increased ATP and NADH concentrations and decreased the proportion of active pyruvate dehydrogenase. The decrease in active dehydrogenase was somewhat greater in mitochondria prepared from hearts of diabetic rats than in those from hearts of non-diabetic rats. Pyruvate (0.1-10 mM) or dichloroacetate (4-50 muM) increased the proportion of active dehydrogenase in isolated mitochondria presumably by inhibition of the pyruvate dehydrogenase kinase reaction. They were much less effective in mitochondria from the hearts of diabetic rats than in those of non-diabetic rats. 4. The matrix water space was increased in preparations of mitochondria from hearts of diabetic rats. Dichloroacetate was concentrated in the matrix water of mitochondria of non-diabetic rats (approx. 16-fold at 10 muM); mitochondria from hearts of diabetic rats concentrated dichloroacetate less effectively. 5. The pyruvate dehydrogenase phosphate phosphatase activity of rat hearts and of rat heart mitochondria (approx. 1-2 munit/unit of pyruvate dehydrogenase) was not affected by diabetes. 6. The rate of oxidation of [1-14C]pyruvate by rat heart mitochondria (6.85 nmol/min per mg of protein with 50 muM-pyruvate) was approx. 46% of the Vmax. value of extracted pyruvate dehydrogenase (active form). Palmitoyl-L-carnitine, which increased the ratio of [acetyl-CoA]/[CoA] 16-fold, inhibited oxidation of pyruvate by about 90% without changing the proportion of active pyruvate dehydrogenase.
334 citations
TL;DR: Synthetic peptides, representing part of the phosphorylatable site of rat liver pyruvate kinase, were phosphorylated by (32P)ATP and the catalytic subunit of cyclic AMP-stimulated protein kinase.
198 citations
TL;DR: Observations can be explained by a phosphorylation of pyruvate kinase by cyclic-AMP-dependent protein kinase, as described by Ljungström et al, which offers a molecular explanation for the hormonal control of gluconeogenesis.
Abstract: Treatment of isolated rat hepatocytes with saturating concentrations of glucagon caused several modifications properties of pyruvate kinase (ATP:pyruvate 2-O-phosphotransferase, EC 2.7.1.40): S0.5 (substrate concentration at half maximum velocity) for phosphoenolpyruvate was about doubled, whereas Vmax was not changed; the activity measured at 0.15 mM phosphoenolpyruvate (physiological concentration) was reduced 65-80%; and there was also an increase in the Hill coefficient and in the affinity of the enzyme for the inhibitors Mg-ATP and alanine. Glucagon, 3':5'-cyclic AMP, and epinephrine caused an inactivation of pyruvate kinase together with a sitmulation of gluconeogenesis. Insulin (10 nM) antagonized the effect of suboptimal doses of glucagon or cyclic AMP and of even maximal doses of epinephrine, on both pyruvate kinase activity and on gluconeogenesis. These observations can be explained by a phosphorylation of pyruvate kinase by cyclic-AMP-dependent protein kinase, as described by Ljungstrom et al. [(1974) Biochim. Biophys. Acta 358, 289-298] in a reconstructed system. They offer a molecular explanation for the hormonal control of gluconeogenesis. Glucose caused an inhibition of gluconeogenesis with no corresponding change in pyruvate kinase activity.
187 citations
TL;DR: The changes in the kinetic properties of hepatic pyruvate kinase which follow treating the perfused rat liver with glucagon or cyclic AMP are consistent with the changes observed in the enzyme properties upon phosphorylation in vitro by a clyclicAMP-stimulated protein kinase.
152 citations
TL;DR: The 2' , 3'-dialdehyde derivative of ATP (oATP) was prepared by periodate oxidation and on the following criteria was considered to be an effective affinity label and was shown to be a linear competitive inhibitor with respect to MgATP2.
Abstract: The 2′,3′-dialdehyde derivative of ATP (oATP) was prepared by periodate oxidation and on the following criteria was considered to be an effective affinity label. The magnesium complex of this derivative (Mg-oATP2−) was shown to be a linear competitive inhibitor with respect to MgATP2− in both the acetyl-CoA-dependent and -independent activities of the enzyme but was a non-competitive inhibitor with respect to bicarbonate, and an uncompetitive inhibitor with respect to pyruvate. Mg-oATP was covalently bound to pyruvate carboxylase by reduction using sodium borohydride with concurrent irreversible inactivation of the enzyme. Although bicarbonate, pyruvate and oxaloacetate were ineffective, both MgATP2− and acetyl-CoA protected the enzyme against this chemical modification. At 100% inactivation, 1.1 ± 0.1 mol of Mg-oATP2− were bound to the enzyme per mole of biotin. Acetyl-CoA had no effect on this stoichiometry.
Chromatography of samples of an enzymic digest of Mg-o[14C]ATP2− -labelled enzyme revealed one major band of radioactivity which co-chromatographed with authentic Lys-oATP.
135 citations
TL;DR: Results indicate that the inactivation of pyruvate dehydrogenase by fatty acid in isolated rat liver mitochondria may be mediated through effects of the NADH/NAD+ ratio and the acetyl-CoA/CoASH ratio on the interconversion of the active and inactive forms of the enzyme complex catalyzed by pyruVate dehydrogensase kinase and pyruviate dehydrationase phosphatase.
118 citations
TL;DR: In hepatocytes isolated from fed rats an inverse correlation between the mitochondrial ATP/ADP ratio and the active form of pyruvate dehydrogenase was demonstrable on loading with fructose, glycerol or sorbitol, and Physiological values were obtained when the hepatocytes were incubated with albumin-oleate, which yielded the highest mitochondrial ATP-ADP ratios.
Abstract: 1. Cytosolic and mitochondrial ATP and ADP concentrations of liver cells isolated from normal fed, starved and diabetic rats were determined. 2. The cytosolic ATP/ADP ratio was 6,9 and 10 in normal fed, starved and diabetic rats respectively. 3. The mitochondrial ATP/ADP ratio was 2 in normal and diabetic rats and 1.6 in starved rats. 4. Adenosine increased the cytosolic and lowered the mitochondrial ATP/ADP ratio, whereas atractyloside had the opposite effect. 5. Incubation of the hepatocytes with fructose, glycerol or sorbitol led to a fall in the ATP/ADP ratio in both the cytosolic and the mitochondrial compartment. 6. The interrelationship between the mitochondrial ATP/ADP ratio and the phosphorylation state of pyruvate dehydrogenase in intact cells was studied. 7. In hepatocytes isolated from fed rats an inverse correlation between the mitochondrial ATP/ADP ratio and the active form of pyruvate dehydrogenase (pyruvate dehydrogenase a) was demonstrable on loading with fructose, glycerol or sorbitol. 8. No such correlation was obtained with pyruvate or dihydroxyacetone. For pyruvate, this can be explained by inhibition of pyruvate dehydrogenase kinase. 9. Liver cells isolated from fed animals displayed pyruvate dehydrogenase a activity twice that found in vivo. Physiological values were obtained when the hepatocytes were incubated with albumin-oleate, which also yielded the highest mitochondrial ATP/ADP ratio.
117 citations
TL;DR: The results suggest that interconversion of the phosphorylated and dephosphorylated forms of pyruvate dehydrogenase plays a major role in the regulation of pyrivate oxidation by eomparison of enzyme activity with measurements of lactate oxidation in the perfused hindquarter.
Abstract: 1. The interconversion of pyruvate dehydrogenase between its inactive phosphorylated and active dephosphorylated forms was studied in skeletal muscle. 2. Exercise, induced by electrical stimulation of the sciatic nerve (5/s), increased the measured activity of (active) pyruvate dehydrogenase threefold in intact anaesthetized rated within 2 min. No further increase was seen after 15 min of stimulation. 3. In the perfused rat hindquarter, (active) pyruvate dehydrogenase activity was decreased by 50% in muscle of starved and diabetic rats. Exercise produced a twofold increase in its activity in all groups; however, the relative differences between fed, starved and diabetic groups persisted. 4. Perfusion of muslce with acetoacetate (2 mM) decreased (active) pyruvate dehydrogenase activity by 50% at rest but not during exercise. 5. Whole-tissue concentrations of pyruvate and citrate, inhibitors of (active) pyruvate dehydrogenase kinase and (inactive) pyruvate dehydrogenase phosphate phosphatase respectively, were not altered by excerise. A decrease in the ATP/ADP ratio was observed, but did not appear to be sufficient to account for the increase in (active) pyruvate dehydrogenase activity. 6. The results suggest that interconversion of the phosphorylated and dephosphorylated forms of pyruvate dehydrogenase plays a major role in the regulation of pyruvate oxidation by eomparison of enzyme activity with measurements of lactate oxidation in the perfused hindquarter [see the preceding paper, Berger et al. (1976)] suggest that pyruvate oxidation is also modulated by the concentrations of substrates, cofactors and inhibitors of (active) pyruvate dehydrogenase activity.
108 citations
TL;DR: The formation of octopine is discussed in relation to anaerobic metabolism which might occur during burst activity in cephalopods and the highest activity yet recorded for this enzyme is shown.
Abstract: The enzymatic activities of glyceraldehyde-3-phosphate dehydrogenase, octopine dehydrogenase and lactate dehydrogenase were determined fromLoligo vulgaris. Octopine dehydrogenase displays the highest activity yet recorded for this enzyme, exceeding glyceraldehyde-3-phosphate dehydrogenase sixfold and lactate dehydrogenase 365-fold (Table 1).
106 citations
TL;DR: It is concluded that alpha-Cyanocinnamate and its derivates, potent and reversible inhibitors of pyruvate transport, react reversibly with mercaptoethanol and cysteine to form addition products.
Abstract: Pyruvate transport into rat liver mitochondria is inhibited by a variety of thiol reagents. alpha-Cyanocinnamate and its derivates, potent and reversible inhibitors of pyruvate transport, react reversibly with mercaptoethanol and cysteine to form addition products. It is concluded that these inhibitors react with an essential thiol group on the pyruvate carrier.
105 citations
TL;DR: The variation in activity of pyruvate dehydrogenase with ADP/ATP ratio is described in the absence of changes in the other two ratios, conditions which were not met in earlier studies which employed the oxidation of different substrates to generate changes in all three ratios.
TL;DR: Results are consistent with the hypothesis that pyruvate kinase is regulated by phosphorylation-dephosphorylation reactions and full activity was restored when phosphorylated pyruve kinase was dephosphorylated by a histone phosphatase from the soluble fraction of rat liver.
TL;DR: The extramitochondrial activity of pyruvate dehydrogenase phosphate phosphatase in rat epididymal fat-pads was sensitive to activation by Ca2+, but perhaps less sensitive than the mitochondrial activity.
Abstract: 1. Pyruvate dehydrogenase phosphate phosphatase activity in rat epididymal fat-pads was measured by using pig heart pyruvate dehydrogenase [32P]phosphate. About 80% was found to be extramitochondrial and therefore probably not directly concerned with the regulation of pyruvate dehydrogenase activity. The extramitochondrial activity was sensitive to activation by Ca2+, but perhaps less sensitive than the mitochondrial activity.
TL;DR: Variation of the nature of the divalent cation at both sites in the presence of ATP causes a sevenfold variation in the rate of detritiation or pyruvate that correlates with the pKa of the metal-bound water.
Abstract: Rabbit muscle pyruvate kinase requires two divalent cations per active site for catalysis of the enolization of pyruvate in the presence of adenosine 5'-triphosphate (ATP). One divalent cation is bound directly to the enzyme and forms a second sphere complex with the bound ATP (site 1). The second divalent cation is directly coordinated to the phosphoryl groups of ATP and does not interact with the enzyme (site 2). The essential role of the divalent cation at site 1 is shown by the requirement for Mg2+ or Mn2+ for the enolization of pyruvate in the presence of the substitution inert Cr3+-ATP complex. The rate of detritiation of pyruvate shows a hyperbolic dependence of Mn2+ concentration in the presence of high concentrations of enzyme and Cr3+-ATP. A dissociation constant for Mn2+ from the pyruvate kinase-Mn2+-ATP-Cr3+-pyruvate complex of 1.3 +/- 0.5 muM is determined by the kinetics of detritiation of pyruvate and by parallel Mn2+ binding studies using electron paramagnetic resonance. The essential role of the divalent cation at site 2 is shown by the sigmoidal dependence of the rate of detritiation of pyruvate on Mn2+ concentration in the presence of high concentrations of enzyme and ATP yielding a dissociation constant of 29 +/- 9 muM for Mn2+ from site 2. This value is similar to the dissociation constant of the binary Mn-ATP complex (14 +/- 6 muM) determined under similar conditions. The rate of detritiation of pyruvate is proportional to the concentration of the pyruvate kinase-Mn2+-ATP-Mn2+-pyruvate complex, as determined by parellel kinetic and binding studies. Variation of the nature of the divalent cation at site 1 in the presence of CrATP causes only a twofold change in the rate of detritiation of pyruvate which does not correlate with the pKa of the metal-bound water. Variation of the nature of the divalent cation at both sites in the presence of ATP causes a sevenfold variation in the rate of detritiation or pyruvate that correlates with the pKa of the metal-bound water. The greater rate of enolization observed with CrATP fits this correlation, indicating that the electrophilicity of the nucleotide bound metal (at site 2) determines the rate of enolization of pyruvate.
TL;DR: The simplest interpretation of these experiments is that NADH reduces the covalently bound lipoyl groups on the transacetylase by means of the associated lipoamide dehydrogenase component, thereby rendering them susceptible to modification.
Abstract: 1. The reaction of the pyruvate dehydrogenase multienzyme complex of Escherichia coli with maleimides was examined. In the absence of substrates, the complex showed little or no reaction with N-ethylmaleimide. However, in the presence of pyruvate and N-ethylmaleimide, inhibition of the pyruvate dehydrogenase complex was rapid. Modification of the enzyme was restricted to the transacetylase component and the inactivation was proportional to the extent of modification. The lipoamide dehydrogenase activity of the complex was unaffected by the treatment. The simplest explanation is that the lipoyl groups on the transacetylase are reductively acetylated by following the initial stages of the normal catalytic cycle, but are thereby made susceptible to modification. Attempts to characterize the reaction product strongly support this conclusion. 2. Similarly, in the presence of N-ethylmaleimide and NADH, much of the pyruvate dehydrogenase activity was lost within seconds, whereas the lipoamide dehydrogenase activity of the complex disappeared more slowly: the initial site of the reaction with the complex was found to be in the lipoyl transacetylase component. The simplest interpretation of these experiments is that NADH reduces the covalently bound lipoyl groups on the transacetylase by means of the associated lipoamide dehydrogenase component, thereby rendering them susceptible to modification. However, the dependence of the rate and extent of inactivation on NADH concentration was complex and it proved impossible to inhibit the pyruvate dehydrogenase activity completely without unacceptable modification of the other component enzymes. 3. The catalytic reduction of 5,5'-dithiobis-(2-nitrobenzoic acid) by NADH in the presence of the pyruvate dehydrogenase complex was demonstrated. A new mechanism for this reaction is proposed in which NADH causes reduction of the enzyme-bound lipoic acid by means of the associated lipoamide dehydrogenase component and the dihydrolipoamide is then oxidized back to the disulphide form by reaction with 5,5'-dithiobis-(2-nitrobenzoic acid). 4. A maleimide with a relatively bulky N-substituent, N-(4-diemthylamino-3,5-dinitrophenyl)maleimide, was an effective replacement for N-ethylmaleimide in these reactions with the pyruvate dehydrogenase complex. 5. The 2-oxoglutarate dehydrogenase complex of E. coli behaved very similarly to the pyruvate dehydrogenase complex, in accord with the generally accepted mechanisms of the two enzymes. 6. The treatment of the 2-oxo acid dehydrogenase complexes with maleimides in the presence of the appropriate 2-oxo acid substrate provides a simple method for selectively inhibiting the transacylase components and for introducing reporter groups on to the lipoyl groups covalently bound to those components.
TL;DR: The results obtained strongly indicate that phosphorylation of pyruvate kinase may also inhibit the enzyme in vivo, which should be important during gluconeogenesis.
TL;DR: Initial-velocity patterns observed with varying TPP concentrations at various fixed concentrations of pyruvate were indicative of either a compulsory order of addition of substrates to form a ternary complex (pyruvates-Enz-TPP) or a random-sequence mechanism in which interconversion of ternARY intermediates is rate-limiting.
Abstract: 1. A method was devised for preparing pig heart pyruvate dehydrogenase free of thiamin pyrophosphate (TPP), permitting studies of the binding of [35S]TPP to pyruvate dehydrogenase and pyruvate dehydrogenase phosphate. The Kd of TPP for pyruvate dehydrogenase was in the range 6.2-8.2 muM, whereas that for pyruvate dehydrogenase phosphate was approximately 15 muM; both forms of the complex contained about the same total number of binding sites (500 pmol/unit of enzyme). EDTA completely inhibited binding of TPP; sodium pyrophosphate, adenylyl imidodiphosphate and GTP, which are inhibitors (competitive with TPP) of the overall pyruvate dehydrogenase reaction, did not appreciably affect TPP binding. 2. Initial-velocity patterns of the overall pyruvate dehydrogenase reaction obtained with varying TPP, CoA and NAD+ concentrations at a fixed pyruvate concentration were consistent with a sequential three-site Ping Pong mechanism; in the presence of oxaloacetate and citrate synthase to remove acetyl-CoA (an inhibitor of the overall reaction) the values of Km for NAD+ and CoA were 53+/- 5 muM and 1.9+/-0.2 muM respectively. Initial-velocity patterns observed with varying TPP concentrations at various fixed concentrations of pyruvate were indicative of either a compulsory order of addition of substrates to form a ternary complex (pyruvate-Enz-TPP) or a random-sequence mechanism in which interconversion of ternary intermediates is rate-limiting; values of Km for pyruvate and TPP were 25+/-4 muM and 50+/-10 nM respectively. The Kia-TPP (the dissociation constant for Enz-TPP complex calculated from kinetic plots) was close to the value of Kd-TPP (determined by direct binding studies). 3. Inhibition of the overall pyruvate dehydrogenase reaction by pyrophosphate was mixed non-competitive versus pyruvate and competitive versus TPP; however, pyrophosphate did not alter the calculated value for Kia-TPP, consistent with the lack of effect of pyrophosphate on the Kd for TPP. 4. Pyruvate dehydrogenase catalysed a TPP-dependent production of 14CO2 from [1-14C]pyruvate in the absence of NAD+ and CoA at approximately 0.35% of the overall reaction rate; this was substantially inhibited by phosphorylation of the enzyme both in the presence and absence of acetaldehyde (which stimulates the rate of 14CO2 production two- or three-fold). 5. Pyruvate dehydrogenase catalysed a partial back-reaction in the presence of TPP, acetyl-CoA and NADH. The Km for TPP was 4.1+/-0.5 muM. The partial back-reaction was stimulated by acetaldehyde, inhibited by pyrophosphate and abolished by phosphorylation. 6. Formation of enzyme-bound [14C]acetylhydrolipoate from [3-14C]pyruvate but not from [1-14C]acetyl-CoA was inhibited by phosphorylation. Phosphorylation also substantially inhibited the transfer of [14C]acetyl groups from enzyme-bound [14C]acetylhydrolipoate to TPP in the presence of NADH. 7...
TL;DR: It was found that adenosylmethionine is reductively processed during activation of pyruvate formate-lyase to yield methionine, adenine and 5-deoxyribose and it is suggested that transientAdenosylation of enzyme II is required for its function as a converter enzyme.
TL;DR: This paper showed that the effect of glucagon to inhibit hepatocyte pyruvate kinase may be mediated at least in part by a phosphorylation-dephosphorylation mechanism.
TL;DR: The properties of each enzyme from all the strains, including S. lactis 7962, were similar, suggesting that the rapid and homolactic fermentation of lactose that is characteristic of group N streptococci is dependent upon a functional PEP-dependent PTS and the presence of beta-Pgal.
Abstract: Group N streptococci, which have the lactose phosphoenolpyruvate (PEP)-dependent phosphotransferase system (PTS) and phospho-β-d-galactosidase (β-Pgal), grew rapidly on lactose and converted more than 90% of the sugar to l-lactate. In contrast, Streptococcus lactis 7962, which does not have a β-Pgal, grew slowly on lactose and converted only 15% of the sugar to l-lactate. With glucose and galactose, this strain had growth rates and fermentation patterns similar to those of other S. lactis strains, suggesting that the rapid and homolactic fermentation of lactose that is characteristic of group N streptococci is dependent upon a functional PEP-dependent PTS and the presence of β-Pgal. Seventeen strains of group N streptococci were examined for the activator specificities of pyruvate kinase and lactate dehydrogenase. The properties of each enzyme from all the strains, including S. lactis 7962, were similar. Pyruvate kinase had a broad activator specificity, whereas activation of lactate dehydrogenase was specific for ketohexose diphosphate. All intermediates of lactose metabolism from the hexose phosphates to the triose phosphates activated pyruvate kinase. No activation was obtained with adenosine 5′-monophosphate. K+ and Mg2+ were required for pyruvate kinase activity but could be replaced by NH4+ and Mn2+, respectively. Lactate dehydrogenase was activated equally by fructose-1,6-diphosphate and tagatose-1,6-diphosphate, the activation characteristics being pH dependent. The roles of pyruvate kinase and lactate dehydrogenase in the regulation of lactose fermentation by group N streptococci are discussed.
TL;DR: Treatment of mice with ether, morphine, ethanol, or diazepam did not change the proportion of pyruvate dehydrogenase in the active form although these treatments have been reported to alter pyruVate oxidation in brain in vivo, unless they also altered energy charge.
Abstract: —The activity of pyruvate dehydrogenase in the brains of mice frozen in liquid nitrogen was 14·0 nmol/min per mg protein. It rose to 23·8 nmol/min per mg protein after incubation of the brain homogenate with 10mm-MgCl2 to activate (dephosphorylate) the enzyme, indicating that approx 60% of the enzyme was originally in the active form. Treatment with amobarbital or pentobarbital halved the proportion of pyruvate dehydrogenase in the active form. The proportion of pyruvate dehydrogenase in the active form increased during ischemia, activation being complete within one min. Anesthesia with amobarbital slowed the activation during ischemia but did not alter the total amount of pyruvate dehydrogenase activity. The concentration of ATP, the ATP/ADP ratio and the adenylate energy charge increased as the proportion of pyruvate dehydrogenase in the active form decreased during barbiturate anesthesia, and they decreased as the proportion of pyruvate dehydrogenase in the active form increased during ischemia. After treatment with insulin, the proportion of pyruvate dehydrogenase in the active form increased by 30%. but the energy charge did not change. Treatment of mice with ether, morphine, ethanol, or diazepam did not change the proportion of pyruvate dehydrogenase in the active form although these treatments have been reported to alter pyruvate oxidation in brain in vivo. Treatments which altered pyruvate oxidation in the brain did not consistently alter the proportion of pyruvate dehydrogenase in the active form, unless they also altered energy charge.
TL;DR: This technique, which uses cu-cyano-3-hydroxy-cinnamic acid as an ‘inhibitor-stop’, has the merit (in comparison with other methods) of measuring initial rates of uptake along a controlled pH gradient at temperatures near to physiological and suggests that such a pyruvate/dicarboxylate exchange does occur and that it probably involves the pyruVate carrier only.
TL;DR: The energy-linked regulation of pyruvate dehydrogenase in intact tissue is possibly mediated by the equilibrium relations between the cellular redox state and the phosphorylation potential recently confirmed in cardiac tissue.
TL;DR: The pyruvate kinase (ATP: pyruVate 2-O-phosphotransferase, EC 2.7.1.40) of Streptococcus lactis C10 is activated by fructose 1, 6-diphosphate (Fru-1,6-P2), activity being a sigmoidal function of activator concentration.
TL;DR: Evidence is reported against the hypothesis that the effect of insulin is brought about by an inhibition of the kinase caused by a lowering of the mitochondrial concentration ratio ATP:ADP, as well as against the possibility that insulin may act through activation of the phosphatase by an increase in mitochondrial Ca2+ concentration.
Abstract: Incorporation of 32Pi into pyruvate dehydrogenase phosphate in mitochondria from control and insulin-treated adipose tissue
TL;DR: The occurrence and levels of activity of various enzymes of carbohydrate catabolism in culture forms (promastigotes) of 4 human species of Leishmania were compared and no evidence could be found for the production of lactic acid by growing cultures and lactic acids could not be detected either in cell-free preparations or after incubation of cell- free extracts with pyruvate and NADH under appropriate conditions.
Abstract: SYNOPSIS. The occurrence and levels of activity of various enzymes of carbohydrate catabolism in culture forms (promastigotes) of 4 human species of Leishmania (L. brasiliensis, L. donovani, L. mexicana, and L. tropica) were compared. These organisms possess enzymes of the Embden-Meyerhof pathway but lack lactate dehydrogenase. No evidence could be found for the production of lactic acid by growing cultures and lactic acid could not be detected either in cell-free preparations or after incubation of cell-free extracts with pyruvate and NADH under appropriate conditions. All 4 species possess α-glycerophosphate dehydrogenase and α-glycerophosphate phosphatase which together could regenerate NAD, thus compensating for the absence of lactate dehydrogenase. The oxidative and nonoxidative reactions of the hexose monophosphate pathway are present in all 4 species. Cell-free extracts have pyruvate dehydrogenase activity which allows the entry of pyruvate into and its subsequent oxidation through the tricarboxylic acid cycle. All enzymes of this cycle, including a thiamine pyrophosphate dependent α-ketoglutarate dehydrogenase are present. Both NAD and NADP-linked malate dehydrogenase activities are present. The isocitrate dehydrogenase is NADP specific. There is an active glutamate dehydrogenase which could compete with α-ketoglutarate dehydrogenase for the common substrate (α-ketoglutarate). Replenishment of C4 acids is accomplished by heterotrophic CO2 fixation catalyzed by pyruvate carboxylase. All 4 species have high levels of NADH oxidase activity. Several enzymes thus far not found in any species of Leishmania have been demonstrated. These are: phosphoglucose isomerase, triose phosphate isomerase, fructose-1, 6-diphosphatase, 3-phosphoglycerate kinase, enolase, α-glycerophosphate dehydrogenase, α-glycerophosphate phosphatase, pyruvate dehydrogenase complex, citrate synthase, aconitase, α-ketoglutarate dehydrogenase, glutamate dehydrogenase, and NADH oxidase.
TL;DR: Observations indicate that stimulation of liver and kidney pyruvate dehydrogenase kinase activities are mediated through the reduction and acetylation of the lipoyl moiety of the dihydrolipoyl transacetylase.
Journal Article•
TL;DR: It is concluded that the P-enolpyruvate cycle is under comparable acute hormonal control as the FDPase-PFK cycle, linked by the common effector Fru-1,6-P2 making not only direct but also indirect hormonal control of pyruVate kinase flux possible.
TL;DR: The stimulation of fatty acids synthesis by dichloroacetate suggests that the activity of pyruvate dehydrogenase can be rate determining for fatty acid synthesis in isolated liver cells.