Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.1.1 (hexokinase)
5,274 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. The mechanism by which insulin activates pyruvate dehydrogenase in rat epididymal adipose tissue was further investigated. 2. When crude extracts, prepared from tissue segments previously exposed to insulin (2m-i.u/ml) for 2min, were supplemented with Mg-2+, Ca-2+, glucose and hexokinase and incubated at 30 degrees C, they displayed an enhanced rate of increase in pyruvate dehydrogenase activity compared with control extracts. 3. When similar extracts were instead supplemented with fluoride, ADP, creatine phosphate and creatine kinase, the rate of decrease in pyruvate dehydrogenase activity observed during incubation at 30 degrees C was unaffected by insulin treatment. 4. It is suggested that insulin increases the fraction of pyruvate dehydrogenase present in the tissue in the active dephospho form by increasing the activity of pyruvate dehydrogenase phosphate phosphatase.
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PMID:Activation of pyruvate dehydrogenase in adipose tissue by insulin. Evidence for an effect of insulin on pyruvate dehydrogenase phosphate phosphatase. 16 82

The mechanism by which fatty acid addition leads to the inactivation of pyruvate dehydrogenase in intact rat liver mitochondria was investigated. In all cases the fatty acid octanoate was added to mitochondria oxidizing succinate. Addition of fatty acid caused an inactivation of pyruvate dehydrogenase in mitochondria incubated under State 3 conditions (glucose plus hexokinase), in uncoupled, oligomycin-treated mitochondria, and in rotenone-menadione-treated mitochondria, but not in uncoupled mitochondria or in mitochondria incubated under State 4 conditions. A number of metabolic conditions were found in which pyruvate dehydrogenase was inactivated concomitant with an elevation in the ATP/ADP ratio. This is consistent with the inverse relationship between the ATP/ADP ratio and the pyruvate dehydrogenase activity proposed by various laboratories. However, in several other metabolic conditions pyruvate dehydrogenase was inactivated while the ATP/ADP ratio either was unchanged or even decreased. This observation implies that there are likely other regulatory factors involved in the fatty acid-mediated inactivation of pyruvate dehydrogenase. Incubation conditions in State 3 were found in which the ATP/ADP and the acetyl-CoA/CoASH ratios remained constant and the pyruvate dehydrogenase activity was correlated inversely with the NADH/NAD+ ratio. Other State 3 conditions were found in which the ATP/ADP and the NADH/NAD+ ratios remained constant while the pyruvate dehydrogenase activity was correlated inversely with the acetyl-CoA/CoASH ratio. Further evidence supporting these experiments with intact mitochondria was the observation that the pyruvate dehydrogenase kinase activity of a mitochondrial extract was stimulated strongly by acetyl-CoA and was inhibited by NAD+ and CoASH. In contrast to acetyl-CoA, octanoyl-CoA inhibited the kinase activity. These 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 dehydrogenase kinase and pyruvate dehydrogenase phosphatase.
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PMID:Regulation of pyruvate dehydrogenase by fatty acid in isolated rat liver mitochondria. 17 49

Hyperinsulinemia was produced in fetal rhesus monkeys for 21 days in the last third of gestation by subcutaneous pork insulin injected at 19 U a day. Plasma insulin concentrations in treated fetuses (N = 4) were 3525 microU/ml. There was no difference in paired pre- and post-treatment fetal plasma glucose concentration. Activity of the hepatic enzymes that promote glucose utilization (glucokinase and hexokinase) and glycolysis (phosphofructokinase, pyruvate kinase, and pyruvate dehydrogenase) was unaffected. Similarly, glycogen metabolism enzymes (active and inactive synthase and phosphorylase) were unaltered. Two gluconeogenic enzymes (PEPCK and glucose-6-phosphatase) were diminished in the treated group compared with controls. Fetal hyperinsulinemia enhanced lipogenic and NADPH-producing enzyme activities, as evidenced by a twofold increase in fatty acid synthase and in citrate cleavage enzyme activity. Malic enzyme was absent. Hyperinsulinemia with euglycemia (1) increases the activity of enzymes that participate in lipogenesis, (2) decreases some of those controlling gluconeogenesis, and (3) has no effect on the enzymes of glycolysis.
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PMID:Chronic hyperinsulinemia in the fetal rhesus monkey: effects on hepatic enzymes active in lipogenesis and carbohydrate metabolism. 22 50

The oxidation of an optimal concentration of palmitoyl-carnitine, buffered with bovine serum albumin, by isolated rat heart mitochondria was found to give rise to an inactivation of pyruvate dehydrogenase, provided that the concentration of pyruvate present in the mitochondrial incubation was less than 250 muM. The greatest degree of inactivation was found at the lowest pyruvate concentration used, 50 muM, and this concentration was adopted for further studies in which the rate of mitochondrial respiration was varied. This was done by varying the activity of added hexokinase, in the presence of ATP, MgCl2, and glucose, and thus the availability of ADP to the mitochondrion. The pyruvate concentration in the incubation was approximately stabilized by adding pyruvate on the basis of oxygen consumption, with the ratio of pyruvate consumed:O2 consumed determined by trial and error. This device allowed the maintenance of essentially steady pyruvate concentrations and ATP/ADP ratios for at least 5 min, and allowed the pyruvate dehydrogenase interconversion time to approach a steady state. Activities of pyruvate dehydrogenase after 5 or 6 min of respiration were as follows, with values given in nanomoles/min/mg of protein for incubations containing pyruvate as sole substrate, and values for incubations containing pyruvate plus palmitoylcarnitine given in parentheses: State 4, 27 (9); 55% of State 3, 54 (14); 85% of State 3, 73 (28); State 3, 90 (93). Respiratory states are defined by Chance and Williams (1955) J. Biol. Chem. 217, 409-427). Values at earlier time points are also presented so that some idea may be formed of the time course of pyruvate dehydrogenase inactivation. CoASH/acetyl-CoA, NAD+/NADH, and ATP/ADP ratios were measured at the same time points in precisely scaled up incubations. The presence of palmitoylcarnitine in State 4 was found to give essentially no change in NAD+/NADH and ATP/ADP ratios and thus the inactivation of pyruvate dehydrogenase in that state may be attributed to a decreased CoASH/acetyl-CoA ratio. At a respiratory rate of 85% of State 3, palmitoylcarnitine did not change the ATP/ADP ratio, but lowered both CoASH/acetyl-CoA and NAD+/NADH ratios, both of which may contribute to pyruvate dehydrogenase inactivation. In State 3 there was no pyruvate dehydrogenase inactivation, despite a lowered CoASH/acetyl-CoA ratio in the presence of palmitoylcarnitine. It is concluded that ATP/ADP ratio has a pronounced effect on the interconversion of active and inactive pyruvate dehydrogenase, in according with previous work. Moreover, at a given ATP/ADP ratio, the effects of palmitoylcarnitine oxidation on enzyme interconversion are consistent with a mechanism involving the modulation of the interconversion by NAD+/NADH and CoASH/acetyl-CoA ratios...
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PMID:Studies on inactivation of pyruvate dehydrogenase by palmitoylcarnitine oxidation in isolated rat heart mitochondria. 83 28

1. The development of pyruvate dehydrogenase and citrate synthase activity in rat brain mitochondria was studied. Whereas the citrate synthase activity starts to increase at about 8 days after birth, that of pyruvate dehydrogenase starts to increase at about 15 days. Measurements of the active proportion of pyruvate dehydrogenase during development were also made. 2. The ability of rat brain mitochondria to oxidize pyruvate follows a similar developmental pattern to that of the pyruvate dehydrogenase. However, the ability to oxidize 3-hydroxybutyrate shows a different developmental pattern (maximal at 20 days and declining by half in the adult), which is compatible with the developmental pattern of the ketone-body-utilizing enzymes. 3. The developmental pattern of both the soluble and the mitochondrially bound hexokinase of rat brain was studied. The total brain hexokinase activity increases markedly at about 15 days, which is mainly due to an increase in activity of the mitochondrially bound form, and reaches the adult situation (approx. 70% being mitochondrial) at about 30 days after birth. 4. The release of the mitochondrially bound hexokinase under different conditions by glucose 6-phosphate was studied. There was insignificant release of the bound hexokinase in media containing high KCl concentrations by glucose 6-phosphate, but in sucrose media half-maximal release of hexokinase was achieved by 70mum-glucose 6-phosphate 5. The production of glucose 6-phosphate by brain mitochondria in the presence of Mg(2+)+glucose was demonstrated, together with the inhibition of this by atractyloside. 6. The results are discussed with respect to the possible biological significance of the similar developmental patterns of pyruvate dehydrogenase and the mitochondrially bound kinases, particularly hexokinase, in the brain. It is suggested that this association may be a mechanism for maintaining an efficient and active aerobic glycolysis which is necessary for full neural expression.
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PMID:Development of mitochondrial energy metabolism in rat brain. 88 Feb 41

Factors which influence the distribution of pyruvate dehydrogenase between its active, unphosphorylated form (PDHa) and its inactive, phosphorylated form (PDHb) have been examined in isolated rat liver mitochondria. A rapid freezing method was developed for the extraction of pyruvate dehydrogenase from incubated mitochondria which prevented interconversions between PHDa and PDHb which normally occur when mitochondria are collected by centrifugal methods. The intramitochondrial ATP:ADP ration was varied over a 100-fold range by the addition of dinitrophenol, oligomycin, or both substances to mitochondria oxidizing 2-oxoglutarate. PDHa activity was found to be inversely proportional to the intramitochondrial ATP:ADP ratio but was not closely correlated with the extramitochondrial adenine nucleotide levels. When mitochondria were incubated in State 4 with succinate and rotenone, the addition of pyruvate increased PDHa activity more than 10-fold without appreciably altering the mitochondrial ATP:ADP ratio. These observations are most readily explained by the known inhibitory effects of pyruvate and ADP on PDHa kinase. PDHa activity could be maintained at a high level by incubating mitochondria in a condition resembling State 3 by the addition of succinate, glucose, and hexokinase. The further addition of octanoate reduced PDHa activity by 60% without appreciably altering the ATP:ADP ratio. Rotenone had a sililar effect. When added in the presence of octanoate, rotenone further decreased PDHa activity whereas 4-pentenoate led to an increase in activity. The effects of octanoate on PDHa activity were not seen when mitochondria were incubated in the presence of high levels of pyruvate, though pyruvate oxidation was till diminished by over 50%. The data suggest that octanoate addition favors the PDHa kinase reaction leading to inactivation of PDHa, and in addition causes the accumulation of NADH and acetyl-CoA which are recognized competitive inhibitors of pyruvate dehydrogenase.
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PMID:Regulation of pyruvate dehydrogenase in isolated rat liver mitochondria. Effects of octanoate, oxidation-reduction state, and adenosine triphosphate to adenosine diphosphate ratio. 111 96

mRNA steady-state levels and activities of enzymes of intermediary carbon metabolism (hexokinase, phosphoglucoisomerase, phosphofructokinase, glucose-6-phosphate dehydrogenase, phosphoglucomutase) and glucose-regulated enzymes (pyruvate decarboxylase, pyruvate dehydrogenase, invertase, alcohol dehydrogenase) were determined in glucose-limited continuous cultures of an industrial strain of Saccharomyces cerevisiae at different dilution rates (D) ranging from 0.05 to 0.315 h-1. The activity of most enzymes measured remained constant over this range except for alcohol dehydrogenase I/II which decreased proportionally with increasing dilution rate. A decrease in phosphoglucomutase activity occurred with increasing dilution rate but reached a minimum at D 0.2 h-1 and from thereon remained constant. A decrease in pyruvate decarboxylase activity and a slight decrease in phosphoglucoisomerase activity was observed. At D 0.29/0.315 h-1, at the onset of the Crabtree effect, most glycolytic enzymes remained constant except for pyruvate decarboxylase and glucose-6-phosphate dehydrogenase which increased at D 0.315 h-1 and alcohol dehydrogenase I/II which decreased. The ADHI/II and PDC1 mRNA levels obtained at the different dilution rates were in accordance with the activity measurements. The mRNA level of HXK1 decreased with increasing dilution rates, whereas the transcription of HXK2 increased. Pyruvate dehydrogenase (PDA1) and PGI1 mRNA fluctuated but no significant change could be detected. These results indicate that there is no transcriptional or translational regulation of glycolytic flux between D 0.05 h-1 and 0.315 h-1 except at the branch point between oxidative and fermentative metabolism (pyruvate decarboxylase/pyruvate dehydrogenase) at D 0.315 h-1. Surprisingly regulation of the Crabtree effect does not seem to involve transcriptional regulation of PDA1.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Analysis of transcription and translation of glycolytic enzymes in glucose-limited continuous cultures of Saccharomyces cerevisiae. 148 26

A radioactive assay for the determination of pyruvate dehydrogenase complex activity in muscle tissue has been developed. The assay measures the rate of acetyl-CoA formation from pyruvate in a reaction mixture containing NAD+ and CoASH. The acetyl-CoA is determined as [14C]citrate after condensation with [14C]-oxaloacetate by citrate synthase. The method is specific and sensitive to the picomole range of acetyl-CoA formed. In eleven normal subjects, the active form of pyruvate dehydrogenase (PDCa) in resting human skeletal muscle samples obtained using the needle biopsy technique was 0.44 +/- 0.16 (SD) mumol acetyl-CoA.min-1.g-1 wet wt. Total pyruvate dehydrogenase complex (PDCt) activity was determined after activation by pretreating the muscle homogenate with Ca2+, Mg2+, dichloroacetate, glucose, and hexokinase. The mean value for PDCt was 1.69 +/- 0.32 mumol acetyl-CoA.min-1.g-1 wet wt, n = 11. The precision of the method was determined by analyzing 4-5 samples of the same muscle piece. The coefficient of variation for PDCa was 8% and for PDCt 5%.
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PMID:A sensitive radioisotopic assay of pyruvate dehydrogenase complex in human muscle tissue. 179 21

It has been shown previously that glucose-induced insulin release is completely absent in rat pancreatic islets that had been cultured for 1 day at low glucose (1 mM) and that it is restored by culturing islets for a 2nd day at high (20 mM) glucose (MacDonald, M. J., Fahien, L. A., McKenzie, D. I., and Moran, S. M. (1991) Am. J. Physiol. 259, E548-E554). It has been suggested that the incapacitation of glucose's insulinotropism is due to down-regulation of the synthesis of enzymes that process glucose's metabolic signal for insulin release. In the current study, results of metabolic, enzymic, and molecular biologic experiments were each consistent with (an) intramitochondrial site(s) of down-regulation in islets cultured at low glucose. Glucose metabolism was inhibited 80% in islets cultured at 1 mM glucose. The suppression of release of 14CO2 from [6-14C]glucose greater than from [U-14C]glucose greater than [3,4-14C]glucose greater than from [1-14C]glucose in islets cultured at low glucose indicated a mitochondrial site of down-regulation because C-6 of glucose can only be converted to CO2 in the citric acid cycle, whereas C-1 can be released as CO2 in the 6-phosphogluconate dehydrogenase [corrected] reaction, and C-6 of glucose dwells in the citric acid cycle longer than carbons 2-5 of glucose. Since carbons 3 and 4 of glucose can be decarboxylated in the pyruvate dehydrogenase reaction, incomplete suppression of CO2 formation from these carbons is consistent with suppression of pyruvate carboxylation as well as decarboxylation. Formation of 3HOH from [5-3H]glucose was equal in the two groups of islets, indicating that glycolysis as far as phosphoenolpyruvate was intact. This idea was supported by assays which showed that activities of enzymes of the glycolytic pathway between glucokinase/hexokinase and pyruvate kinase were equal in both types of islets. Additional studies indicated that regulation by glucose was at transcription of genes coding for some mitochondrial enzymes. Glucokinase, malic enzyme, and fumarase mRNAs were not affected by glucose, whereas the pyruvate dehydrogenase E1 alpha subunit and pyruvate carboxylase mRNAs were decreased 85-90% in islets cultured at 1 mM glucose. Pyruvate dehydrogenase enzyme activity was decreased to a similar extent in these islets. About 24 h was required for maximal (de)induction of pyruvate dehydrogenase E1 alpha and pyruvate carboxylase mRNAs, and the amounts of transcripts were proportional to the concentrations of glucose between 1 and 20 mM.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Pyruvate dehydrogenase and pyruvate carboxylase. Sites of pretranslational regulation by glucose of glucose-induced insulin release in pancreatic islets. 193 63

Interleukin-1 beta (IL-1 beta) has been implicated in the pathogenesis of insulin-dependent diabetes mellitus. In the present study we have investigated the effects of IL-1 beta on glucose metabolism in clonal HIT-T15 beta cells. In the short-term (1 h), 25 U/ml IL-1 beta significantly increased the rates of insulin release and glucose utilisation, but not glucose oxidation. In contrast, after 48 h, IL-1 beta inhibited insulin release and glucose utilisation and oxidation. By assaying enzymes (hexokinase, glucokinase, pyruvate dehydrogenase, glucose 6-phosphatase) and nucleotides (ATP, ADP) associated with the regulation of glycolysis and glucose oxidation, we conclude that the inhibitory effects of IL-1 beta may be due to impaired glucokinase activity.
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PMID:Interleukin-1 beta inhibits glucokinase activity in clonal HIT-T15 beta-cells. 219 15


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