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)

In a group of ten adult obese subjects, maintained for 15 days on a normal caloric intake and balanced diet, the activity of hexokinase (EC 2.7.1.1),6-phosphofructokinase (EC 2.7.1.11), and ATP citratelyase (EC 4.1.3.8) in the adipose tissue was significantly increased, both on a protein and on a fat cell number basis, compared to matched normal subjects. The activity of glucose-6-phosphate dehydrogenase (EC 1.1.1.49), malate dehydrogenase (EC 1.1.1.37), and malate dehydrogenase (decarboxylating) (NADP) (EC 1.1.1.40), on the other hand, was unchanged. Since both hexokinase and 6-phosphofructokinase are rate-limiting in glycolysis, their enhanced activity would indicate the occurrence of an increased capacity to metabolize glucose and therefore to generate alpha-glycerophosphate. The elevation of ATP citrate-lyase would suggest increased lipogenesis, owing to the regulatory role that this enzyme plays in fatty acid synthesis. The normal activity of glucose-6-phosphate dehydrogenase and malate dehydrogenase (decarboxylating) (NADP), which supply NADPH for the reduction of acetyl-CoA to fatty acids, would suggest that the change in lipogenesis is of moderate degree, thereb) affecting only the most rate-limiting enzyme, ATP citrate-lyase. These data, on the whole, are consistent with the occurrence of enhanced triglyceride formation. Whether the enzyme changes observed are adaptive or genetic in nature remains to be clarified.
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PMID:Enzymes related to lipogenesis in the adipose tissue of obese subjects. 13 Dec 32

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

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

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

The steady state mitochondrial content of coenzyme A-SH (CoA), acetyl-CoA, succinyl-CoA, and long chain acyl-CoA has been determined during the oxidation of palmitoylcarnitine by rabbit heart mitochondria. Variation of the substrate concentration during ADP-stimulated (state 3) respiration varies the mitochondrial content of long chain acyl-CoA and the rate of O2 uptake, and permits the conclusion that the Km of beta oxidation for intramitochondrial long chain acyl-CoA is approximately 1 nmol/mg of mitochondrial protein. At near saturating concentrations of palmitoylcarnitine, plus L-malate, the addition of ADP causes a decrease in acetyl-CoA, an increase in CoA and succinyl-CoA, and no clear change in long chain acyl-CoA content. These changes reverse upon the depletion of ADP (state 3 leads to 4 transition). Similar changes in CoA, acetyl-CoA, and succinyl-CoA are seen during state 4 leads to 3 leads to 4 transitions with pyruvate plus L-malate and octanoate plus L-malate as substrates. These results suggest a limitation of flux by citrate synthase during the controlled oxidation of these three substrates. The ratio acetyl-CoA/succinyl-CoA was determined not only during state 3 and state 4 oxidation of palmitoylcarnitine plus L-malate and pyruvate plus L-malate, but also during intermediate respiratory states (state 3 1/2) generated by adding glucose and varying amounts of hexokinase. These intermediate states are characterized by a high succinyl-CoA content, relative to either state 3 or state 4, and a suboptimal flux through citrate synthase, estimated either by pyruvate disappearance or by O2 uptake.
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PMID:The steady state concentrations of coenzyme A-SH and coenzyme A thioester, citrate, and isocitrate during tricarboxylate cycle oxidations in rabbit heart mitochondria. 119 59

The maximum activities of some key enzymes of metabolism were studied in lungs of fed and 48-h-starved rats. The maximum activity of hexokinase in the lung is similar to that of other tissues of the body, but lower than that of phosphorylase and 6-phosphofructokinase. High activities of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase were found in lung tissue, suggesting the importance of the pentose phosphate pathway in the lung. The activities of hexokinase and 6-phosphofructokinase were decreased whereas that of phosphorylase increased in response to starvation. Of the enzymes of the tricarboxylic acid cycle whose activities were measured, that of oxoglutarate dehydrogenase was the lowest, yet its activity (approximately 4.2 nmol/min per mg protein at 37 degrees C) was considerably greater than the flux through the cycle (0.46 nmol/min per mg protein at 37 degrees C; calculated from oxygen consumption by incubated lung slices). The activities of both oxoglutarate dehydrogenase and citrate synthase were decreased by starvation. The activities of 3-oxoacid CoA-transferase and acetoacetyl-CoA thiolase were low in lung tissue compared to those of other tissues (eg kidney, brain) and that of 3-hydroxybutyrate dehydrogenase was very low. The activity of carnitine palmitoyl transferase is higher in the lung, suggesting that fatty acids (and possibly acetoacetate) could provide acetyl-CoA as substrate for the tricarboxylic acid cycle. Very low rates of utilization of 3-hydroxybutyrate were observed during incubation of lung slices, but that of oleate was 1.2 nmol/h per mg of protein.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Metabolism of glucose, glutamine, long-chain fatty acids and ketone bodies by lungs of the rat. 176

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

In order to find the markers of the toxicity of the autoxidized lipids in the liver, rats were given a lethal amount of secondary autoxidation products of linoleic acid (400 mg/rat/day for 3 days) and then changes in the hepatic metabolic functions were analyzed. A decrease in acetyl-CoA level to half caused by the depletion of CoASH was reported in an associated paper (J. Nutr. Sci. Vitaminol., 35, 11-23, 1989). Citrate, isocitrate, and 2-oxoglutarate also decreased to half the level of those of the control group. Reduction in isocitrate dehydrogenase activity was only 25%, while NADH2 and ATP levels remained unchanged. Thus, the reduction in the citrate cycle activity was due to the decrease in acetyl-CoA. The activity of mitochondrial succinate dehydrogenase was decreased to 1/5. Other appreciable changes were depletion of glucose 6-phosphate and fructose 6-phosphate, accumulation of glucose 1-phosphate, reductions in hexokinase, phosphofructokinase, glucose-6-phosphatase, phosphoglucomutase, and phosphogluconate dehydrogenase activities, and decrease in the NADPH2 level. It was considered that these changes were caused by the depletion of glucose 6-phosphate whose synthetic pathways were abnormal. Therefore, the markers of the hepatotoxicity of secondary products were the changes in the CoASH level and the activities of succinate dehydrogenase and synthetic pathways for glucose 6-phosphate.
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PMID:Succinate dehydrogenase and synthetic pathways of glucose 6-phosphate are also the markers of the toxicity of orally administered secondary autoxidation products of linoleic acid in rat liver. 254 8

Energy metabolism in proliferating cultured rat thymocytes was compared with that of freshly prepared non-proliferating resting cells. Cultured rat thymocytes enter a proliferative cycle after stimulation by concanavalin A and Lymphocult T (interleukin-2), with maximal rates of DNA synthesis at 60 h. Compared with incubated resting thymocytes, glucose metabolism by incubated proliferating thymocytes was 53-fold increased; 90% of the amount of glucose utilized was converted into lactate, whereas resting cells metabolized only 56% to lactate. However, the latter oxidized 27% of glucose to CO2, as opposed to 1.1% by the proliferating cells. Activities of hexokinase, 6-phosphofructokinase, pyruvate kinase and aldolase in proliferating thymocytes were increased 12-, 17-, 30- and 24-fold respectively, whereas the rate of pyruvate oxidation was enhanced only 3-fold. The relatively low capacity of pyruvate degradation in proliferating thymocytes might be the reason for almost complete conversion of glucose into lactate by these cells. Glutamine utilization by rat thymocytes was 8-fold increased during proliferation. The major end products of glutamine metabolism are glutamate, aspartate, CO2 and ammonia. A complete recovery of glutamine carbon and nitrogen in the products was obtained. The amount of glutamate formed by phosphate-dependent glutaminase which entered the citric acid cycle was enhanced 5-fold in the proliferating cells: 76% was converted into 2-oxoglutarate by aspartate aminotransferase, present in high activity, and the remaining 24% by glutamate dehydrogenase. With resting cells the same percentages were obtained (75 and 25). Maximal activities of glutaminase, glutamate dehydrogenase and aspartate aminotransferase were increased 3-, 12- and 6-fold respectively in proliferating cells; 32% of the glutamate metabolized in the citric acid cycle was recovered in CO2 and 61% in aspartate. In resting cells this proportion was 41% and 59% and in mitogen-stimulated cells 39% and 65% respectively. Addition of glucose (4 mM) or malate (2 mM) strongly decreased the rates of glutamine utilization and glutamate conversion into 2-oxoglutarate by proliferating thymocytes and also affected the pathways of further glutamate metabolism. Addition of 2 mM-pyruvate did not alter the rate of glutamine utilization by proliferating thymocytes, but decreased the rate of metabolism beyond the stage of glutamate significantly. Formation of acetyl-CoA in the presence of pyruvate might explain the relatively enhanced oxidation of glutamate to CO2 (56%) by proliferating thymocytes.
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PMID:Glutamine and glucose metabolism during thymocyte proliferation. Pathways of glutamine and glutamate metabolism. 286 9

In this study we investigated the variations of the maximal activities of the rate-controlling glycolytic enzymes (i.e., hexokinase, HK; phosphofructokinase, PFK; pyruvate kinase, PK) and of the pyruvate-dehydrogenase complex (PDHc) during the early embryogenesis of Xenopus laevis (from cleavage through hatching). All the enzymatic assays, using different coupled reactions, were performed spectrophotometrically on cytosolic and mitochondrial fractions. The maximal HK activity increases markedly from neurulation onwards, PFK activity presents a peak around gastrulation, PK activity remains relatively constant throughout the period studied and the highest PDHc activity is observed during cleavage. The specific activities display the same temporal pattern. Furthermore, in the sequence of reactions by which glucose is degraded to form acetyl-CoA, the maximal activities of PFK and PK are not limiting while those of HK and PDHc could be rate-limiting at relatively late developmental stages (hatching).
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PMID:Changes in activity of the regulatory glycolytic enzymes and of the pyruvate-dehydrogenase complex during the development of Xenopus laevis. 293 70


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