Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.2 (PDK1)
 2,238 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Rat epididymal-adipose-tissue mitochondria were made selectively permeable to small molecules without the loss of matrix enzymes by treating the mitochondria with toluene under controlled conditions. With this preparation the entire pyruvate dehydrogenase system was shown to be retained within the mitochondrial matrix and to retain its normal catalytic activity. By using dilute suspensions of these permeabilized mitochondria maintained in the cuvette of a spectrophotometer, it was possible to monitor changes of pyruvate dehydrogenase activity continuously while the activities of the interconverting kinase and phosphatase could be independently manipulated. Permeabilized mitochondria were prepared from control and insulin-treated adipose tissue, and the properties of both the pyruvate dehydrogenase kinase and the phosphatase were compared in situ. No difference in kinase activity was detected, but increases in phosphatase activity were observed in permeabilized mitochondria from insulin-treated tissue. Further studies showed that the main effect of insulin treatment was a decrease in the apparent Ka of the phosphatase for Mg2+, in agreement with earlier studies with mitochondria made permeable to Mg2+ by using the ionophore A23187 [Thomas, Diggle & Denton (1986) Biochem. J. 238, 83-91]. No effects of spermine were detected, although spermine diminishes the Ka of purified phosphatase preparations for Mg2+. Since effects of insulin on pyruvate dehydrogenase phosphatase activity are not evident in mitochondrial extracts, it is concluded that insulin may act by altering some high-Mr component which interacts with the pyruvate dehydrogenase system within intact or permeabilized mitochondria, but not when the mitochondrial membranes are disrupted.
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PMID:Use of toluene-permeabilized mitochondria to study the regulation of adipose tissue pyruvate dehydrogenase in situ. Further evidence that insulin acts through stimulation of pyruvate dehydrogenase phosphate phosphatase. 302 48

The work investigated the mechanisms for modulation of renal and hepatic pyruvate dehydrogenase complex (PDH) activities after carbohydrate re-feeding of 48 h-starved rats, and identified a regulatory role for tri-iodothyronine. Glucose re-feeding decreased blood concentrations of lipid fuels in both euthyroid and hyperthyroid rats. This treatment was not associated with re-activation of hepatic PDH in either group of rats, or of renal PDH in hyperthyroid rats (where activity was already high), but it increased renal PDH in euthyroid rats. Dichloroacetate (DCA), an activator of PDH kinase, increased renal PDH activities in euthyroid rats, but not hyperthyroid rats, and effects of glucose re-feeding or hyperthyroidism were no longer apparent. These treatments therefore exert their effects on renal PDH through changes in PDH kinase. DCA re-activation of hepatic PDH was more marked in hyperthyroid than in euthyroid rats, suggesting that, under conditions of inhibited kinase activity, PDH phosphatase is more active in livers of hyperthyroid rats. The limited effect of DCA on hepatic PDH in euthyroid rats was potentiated by glucose re-feeding or insulin, but not by inhibition of lipolysis, demonstrating a direct effect of insulin to increase hepatic PDH phosphatase. Glucose re-feeding, inhibition of lipolysis or insulin administration did not increase hepatic PDH in DCA-treated hyperthyroid rats, indicating that effects of hyperthyroidism and of insulin on PDH phosphatase are not additive.
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PMID:Regulation of renal and hepatic pyruvate dehydrogenase complex on carbohydrate re-feeding after starvation. Possible mechanisms and a regulatory role for thyroid hormone. 329 32

Activity of the pyruvate dehydrogenase complex determines the rate of glucose oxidation in animals including man. The complex is regulated by reversible phosphorylation, phosphorylation resulting in inactivation. Activity is therefore dependent upon the activities of pyruvate dehydrogenase kinase and phosphatase. Activity of the complex is reduced in diabetes and starvation as a result of insulin deficiency. The mechanism involves activation of pyruvate dehydrogenase kinase by short-term effects of products of fatty acid oxidation and by longer term effects involving specific protein synthesis; in hepatocytes the signals may include lipid fuels and glucagon. Activity of the branched chain ketoacid dehydrogenase complex determines the rate of degradation of branched chain aminoacids which is adjusted according to dietary supply. The complex is regulated by reversible phosphorylation, phosphorylation being inactivating. In liver and kidney, but not in muscles a protein activator (free E1 component) may reactivate phosphorylated complex without dephosphorylation and facilitate hepatic oxidation of branched chain ketoacids. Metabolic adjustments induced by diet and diabetes include loss of activator protein, loss of total complex activity in liver but not muscles, and enhanced inactivation by phosphorylation in liver.
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PMID:alpha-Ketoacid dehydrogenase complexes and respiratory fuel utilisation in diabetes. 405 46

In heart muscle regulation of pyruvate dehydrogenase (PDH) complex activity by reversible phosphorylation is the major determinant of glucose oxidation under physiological conditions and in diabetes. Altered mitochondrial concentrations of effectors of PDH kinase and phosphatase (metabolites, Ca2+, H+) appear to explain effects of oxidation of lipid fuels, myocardial contraction and ischaemia on PDH complex activity. The effects of diabetes and starvation are mediated in addition by protein(s) which increase the activity of PDH kinase. End product inhibition by NADH may be important in ischaemia.
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PMID:Molecular mechanisms regulating myocardial glucose oxidation. 406 41

This paper reports the discovery that the activity of the multienzyme pyruvate dehydrogenase complex from beef kidney mitochondria is regulated by a phosphorylation-dephosphorylation reaction sequence. The site of this regulation is the pyruvate dehydrogenase component of the complex. Phosphorylation and concomitant inactivation of pyruvate dehydrogenase are catalyzed by an ATP-specific kinase (i.e., a pyruvate dehydrogenase kinase), and dephosphorylation and concomitant reactivation are catalyzed by a phosphatase (i.e., a pyruvate dehydrogenase phosphatase). The kinase and the phosphatase appear to be regulatory subunits of the pyruvate dehydrogenase complex.
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PMID:Alpha-keto acid dehydrogenase complexes. X. Regulation of the activity of the pyruvate dehydrogenase complex from beef kidney mitochondria by phosphorylation and dephosphorylation. 430 45

1. Monochloroacetate, dichloroacetate, trichloroacetate, difluoroacetate, 2-chloropropionate, 2,2'-dichloropropionate and 3-chloropropionate were inhibitors of pig heart pyruvate dehydrogenase kinase. Dichloroacetate was also shown to inhibit rat heart pyruvate dehydrogenase kinase. The inhibition was mainly non-competitive with respect to ATP. The concentration required for 50% inhibition was approx. 100mum for the three chloroacetates, difluoroacetate and 2-chloropropionate and 2,2'-dichloropropionate. Dichloroacetamide was not inhibitory. 2. Dichloroacetate had no significant effect on the activity of pyruvate dehydrogenase phosphate phosphatase when this was maximally activated by Ca(2+) and Mg(2+). 3. Dichloroacetate did not increase the catalytic activity of purified pig heart pyruvate dehydrogenase. 4. Dichloroacetate, difluoroacetate, 2-chloropropionate and 2,2'-dichloropropionate increased the proportion of the active (dephosphorylated) form of pyruvate dehydrogenase in rat heart mitochondria with 2-oxoglutarate and malate as respiratory substrates. Similar effects of dichloroacetate were shown with kidney and fat-cell mitochondria. Glyoxylate, monochloroacetate and dichloroacetamide were inactive. 5. Dichloroacetate increased the proportion of active pyruvate dehydrogenase in the perfused rat heart, isolated rat diaphragm and rat epididymal fat-pads. Difluoroacetate and dichloroacetamide were also active in the perfused heart, but glyoxylate, monochloroacetate and trichloroacetate were inactive. 6. Injection of dichloroacetate into rats starved overnight led within 60 min to activation of pyruvate dehydrogenase in extracts from heart, psoas muscle, adipose tissue, kidney and liver. The blood concentration of lactate fell within 15 min to reach a minimum after 60 min. The blood concentration of glucose fell after 90 min and reached a minimum after 120 min. There was no significant change in plasma glycerol concentration. 7. In epididymal fatpads dichloroacetate inhibited incorporation of (14)C from [U-(14)C]glucose, [U-(14)C]fructose and from [U-(14)C]lactate into CO(2) and glyceride fatty acid. 8. It is concluded that the inhibition of pyruvate dehydrogenase kinase by dichloroacetate may account for the activation of pyruvate dehydrogenase and pyruvate oxidation which it induces in isolated rat heart and diaphragm muscles, subject to certain assumptions as to the distribution of dichloroacetate across the plasma membrane and the mitochondrial membrane. 9. It is suggested that activation of pyruvate dehydrogenase by dichloroacetate could contribute to its hypoglycaemic effect by interruption of the Cori and alanine cycles. 10. It is suggested that the inhibitory effect of dichloroacetate on fatty acid synthesis in adipose tissue may involve an additional effect or effects of the compound.
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PMID:Mechanism of activation of pyruvate dehydrogenase by dichloroacetate and other halogenated carboxylic acids. 447 69

A method is described to measure directly in rat brain the activity of pyruvate dehydrogenase kinase (PDHa kinase; EC 2.7.1.99), which catalyzes the inactivation of pyruvate dehydrogenase complex (PDHC, EC 1.2.4.1, EC 2.3.1.12, and EC 1.6.4.3). The activity showed the expected dependence on added ATP and divalent cation, and the expected inhibition by dichloroacetate, pyruvate, and thiamin pyrophosphate. These results, and the properties of pyruvate dehydrogenase phosphate phosphatase (EC 3.1.3.43), indicate that the mechanisms of control of phosphorylation of PDHC seem qualitatively similar in brain to those in other tissues. Regionally, PDHa kinase is more active in cerebral cortex and hippocampus, and less active in hypothalamus, pons and medulla, and olfactory bulbs. Indeed, the PDHa kinase activity in olfactory bulbs is uniquely low, and is more sensitive to inhibition by pyruvate and dichloroacetate than that in the cerebral cortex. Thus, there are significant quantitative differences in the enzymatic apparatus for controlling PDHC activity in different parts of the brain.
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PMID:Properties and regional distribution of pyruvate dehydrogenase kinase in rat brain. 631 89

Increases in the amount of the active non-phosphorylated form of pyruvate dehydrogenase in rat epididymal adipose tissue, as a result of incubation with insulin, persist not only during the preparation of mitochondria but also during subsequent incubation of coupled mitochondria in the presence of respiratory substrates. No effect on insulin was found if the hormone was added directly to mitochondria in the presence or absence of added plasma membranes. Concentrations of several possible regulators of pyruvate dehydrogenase kinase (ATP, ADP, NADH, NAD+, acetyl-CoA, CoA and potassium) were measured in rat epididymal-adipose-tissue mitochondria incubated under conditions where differences in pyruvate dehydrogenase activity persist as a result of insulin action. No alterations were found, and it is suggested that inhibition of the kinase is not the principal means by which insulin activates pyruvate dehydrogenase. The intramitochondrial concentration of magnesium was also unaffected. Differences in pyruvate dehydrogenase activity in interscapular brown adipose tissue associated with manipulation of plasma insulin concentrations of cold-adapted rats were also shown to persist during the preparation and subsequent incubation of mitochondria in the presence or absence of GDP. It is pointed out that the persistence of the effect of insulin on pyruvate dehydrogenase in incubated mitochondria will facilitate the recognition of the mechanism of this action of the hormone. Evidence that the short-term action of insulin involves an increase in pyruvate dehydrogenase phosphate phosphatase activity rather than inhibition of that of pyruvate dehydrogenase kinase is discussed.
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PMID:Persistence of the effect of insulin on pyruvate dehydrogenase activity in rat white and brown adipose tissue during the preparation and subsequent incubation of mitochondria. 632 Aug 7

The total activity of pyruvate dehydrogenase (PDH) complex in rat hind-limb muscle mitochondria was 76.4 units/g of mitochondrial protein. The proportion of complex in the active form was 34% (as isolated), 8-14% (incubation with respiratory substrates) and greater than 98% (incubation without respiratory substrates). Complex was also inactivated by ATP in the presence of oligomycin B and carbonyl cyanide m-chlorophenylhydrazone. Ca2+ (which activates PDH phosphatase) and pyruvate or dichloroacetate (which inhibit PDH kinase) each increased the concentration of active PDH complex in a concentration-dependent manner in mitochondria oxidizing 2-oxoglutarate/L-malate. Values giving half-maximal activation were 10 nM-Ca2+, 3 mM-pyruvate and 16 microM-dichloroacetate. Activation by Ca2+ was inhibited by Na+ and Mg2+. Mitochondria incubated with [32P]Pi/2-oxoglutarate/L-malate incorporated 32P into three phosphorylation sites in the alpha-chain of PDH; relative rates of phosphorylation were sites 1 greater than 2 greater than 3, and of dephosphorylation, sites 2 greater than 1 greater than 3. Starvation ( 48h ) or induction of alloxan-diabetes had no effect on the total activity of PDH complex in skeletal-muscle mitochondria, but each decreased the concentration of active complex in mitochondria oxidizing 2-oxoglutarate/L-malate and increased the concentrations of Ca2+, pyruvate or dichloracetate required for half-maximal reactivation. In extracts of mitochondria the activity of PDH kinase was increased 2-3-fold by 48 h starvation or alloxan-diabetes, but the activity of PDH phosphatase was unchanged.
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PMID:Reversible phosphorylation of pyruvate dehydrogenase in rat skeletal-muscle mitochondria. Effects of starvation and diabetes. 633 93

Intramitochondrial substrate metabolism was examined in cultured neuroblastoma NB41A3 cells exposed to endotoxin in order to elucidate possible causes for the changes in [ATP]/[ADP][Pi] and [NAD+]/[NADH] reported by us previously in these cells [1]. Flux through pyruvate dehydrogenase (PDH), measured with [1-14C]-pyruvate, was inhibited by 54% within 10 min in endotoxin-treated cells (0.99 nmol/min/mg dry wt vs 0.46 nmol/min/mg dry wt). In contrast, flux through 2-oxoglutarate dehydrogenase, measured with [1-14C]-glutamate was unaltered (0.79 nmol/min/mg dry wt). Dichloroacetate, an inhibitor of PDH kinase, restored flux through PDH to control levels. In endotoxin-treated cells, only 44% of the total PDH complex was in the active (nonphosphorylated) form as compared to 72% in control cells. Equilibrium uptake studies with 45Ca2+ and atomic absorption measurements showed that intracellular [Ca2+] in endotoxin-treated cells was about 20% lower than in control cells. It is postulated that binding of endotoxin to the plasma membrane triggers a sequence of events that lead to an initial decline in intracellular calcium concentration and that this latter event may be responsible for the inhibition of PDH phosphatase and consequent conversion of the complex to its inactive phosphorylated form.
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PMID:Cellular effects of endotoxin in vitro. I. Effect of endotoxin on mitochondrial substrate metabolism and intracellular calcium. 635 31


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