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)

A type C hexokinase (ATP:D-hexose-6-phosphotransferase EC 2.7.1.1) was partially purified from the liver of the frog Calyptocephalella caudiverbera. The enzyme is inhibited by glucose levels in the range of normal blood sugar concentrations. The extent of the inhibition by glucose depends on the concentration of ATP, being most marked between 1 and 5 mM ATP. Fructose, although a substrate, was not inhibitory of its own phosphorylation. The inhibitory effect of high glucose levels exhibited a strong, reversible pH dependence being most marked at pH 6.5. At pH 7.5 the inhibition by high glucose levels was a function of the enzyme concentration, the effect being stronger at high enzyme concentrations, whereas no inhibition was observed when assaying very diluted preparations. At all enzyme concentrations studied, high levels of glucose caused no inhibition at pH 8.5, whereas at pH 6.5 strong inhibition was always observed. Short times of photooxidation of hexokinase C as well as incubation with low concentrations of p-chloromercuribenzoate resulted in the loss of the inhibition by excess of glucose. Glucose-6-phosphate was found to be a strong inhibitor of hexokinase C but only at high glucose levels. The inhibitory effect of glucose-6-P follows sigmoidal kinetics at low (about 0.02 mM) glucose concentrations, the Hill coefficient being 2.3. The kinetics of the inhibition became hyperbolic at high (greater than 0.2 mM) glucose levels. These results suggest that the inhibition of hexokinase C by excess glucose is due to the interaction of glucose with a second, aldose-specific, regulatory site on the enzyme. The modification of the inhibitory effect by ATP, glucose-6-P, enzyme concentration, and pH, all of them at physiological levels, indicates a major role for hexokinase C in the regulation of glucose utilization by the liver.
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PMID:The allosteric regulation of hexokinase C from amphibian liver. 0 52

In the subcommissural organ (SCO) of the guinea pig, rat, golden hamster, and mouse the activity and distribution of enzymes related to the energy-supplying metabolism and of some marker enzymes of different cell organelles have been investigated by means of mostly modified histochemical methods. The results were compared with findings in the ciliated ependyma of the ventricular wall and with those in the ependyma of the choroid plexus of the third ventricle. In the ependymal part of the SCO only a moderate activity of hexokinase is observed in its specialized columnar cells whereas a high activity is present both in the ciliated ependyma and the choroid plexus. - The staining pattern of glucose-6-phosphatase is similar to that of hexokinase but this enzyme is found is the SCO only. - Likewise hexokinase, glycogen granules and enzymes related to glycogen metabolism (phosphoglucomutase, uridine-diphosphoglucose pyrophosphorylase, glycogen synthetase and phosphorylase) are regularly found most numerous and active in the nuclear and supra-nuclear area of the ependymal part. These enzymes are less active in both the other ependymal regions. - Uridine-diphosphoglucose dehydrogenase could not be demonstrated in the SCO. The NADP-linked enzymes of the pentose phosphate shunt, glucose-6-phosphate and 6-phosphogluconate dehydrogenase, show a moderate activity which decreases also from the nuclear towards the apical area of the ependymal cells of the SCO. Enzymes of the glycolytic pathway, such as glucosephosphate isomerase, fructose-6-phosphate kinase, fructose-I,6-diphosphate aldolase, glyceraldehyde-3-phosphate and lactate dehydrogenase, are highly active in the SCO and are located mainly in the supranuclear area, too. Fructose-1,6-diphosphatase could not be demonstrated thus indicating that in the SCO the pathway is most probably only glycolytic but not gluconeogenetic. Compared to the ependyma of the ventricular wall and of the choroid plexus, in the SCO the M type subunits of lactate dehydrogenase predominate. Glycolytic enzymes are also very active in the choroid plexus but less in the ciliated ependyma. Compared to the ciliated ependyma and especially to the ependyma of the choroid plexus, the activities of enzymes which are only present in mitochondria (NAD-linked isocitrate dehydrogenase, succinate dehydrogenase, NAD-linked malate dehydrogenase after preextraction, cytochrome oxidase, 3-hydroxybutyrate and glycerolphosphate and glutamate dehydrogenase) are relatively low. Mitochondria are accumulated near the superior pole of the nuclei as well as in the most apical part of the ependymal cells. - The staining pattern of NADP-linked isocitrate and malate dehydrogenase as well as of NADH dehydrogenase suggests that these enzymes are localized both in and out of mitochondria. The extramitochondrial activity of the first two enzymes might be localized in the cytosol. The extramitochondrial activity of NADH dehydrogenase might be localized in the endoplasmic reticulum...
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PMID:Enzymatic organization of the subcommissural organ. 123 49

1. Time-curves of insulin effects on energy-producing systems in different cellular compartments of rat diaphragm muscle have revealed: (a) a rapid (within minutes) and transient stimulatory effect of insulin on cytoskeletal phosphofructokinase and aldolase and mitochondrial hexokinase. (b) A slower and consistent stimulatory effect on glucose 1,6-bisphosphate level, with concomitant gradual activation of cytosolic phosphofructokinase. Fructose 2,6-bisphosphate levels were not changed by insulin. (c) Lactate concentration correlated with the stimulation of cytoskeletal and cytosolic glycolysis. 2. Calmodulin antagonists, trifluoperazine or CGS 9343B, prevented all these effects of insulin. 3. These results suggest that cytoskeletal glycolysis and mitochondrial oxidation are the source of ATP for the rapid actions of insulin, whereas cytosolic glycolysis is the source of ATP for the slow actions of insulin. Calmodulin is involved in all these effects of insulin.
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PMID:Sequence of insulin effects on cytoskeletal and cytosolic phosphofructokinase, mitochondrial hexokinase, glucose 1,6-bisphosphate and fructose 2,6-bisphosphate levels, and the antagonistic action of calmodulin inhibitors, in diaphragm muscle. 139 93

Most of the enzymes involved in glycolysis are readily reversible and are also active in gluconeogenesis. However, three reaction steps are irreversible, i.e., those catalyzed by hexokinase, phosphofructokinase, and pyruvate kinase; for in each of these reactions there occurs a large negative free-energy change, and these are reactions thus bypassed by alternate enzyme-catalyzed reactions. Pyruvate kinase (EC 2.7.1.40, PK) plays an important role in controlling glycolysis and gluconeogenesis. To clarify the characteristics of glycolysis in dental pulp, we examined the enzymatic properties of pyruvate kinase from pig dental pulp and compared them with those of the enzyme from pig brain. 1) Pyruvate kinase from dental pulp and brain were purified by use of ammonium sulphate fractionation, phosphocellulose colum chromatography, and isoelectric focusing. The prepared enzymes showed a single protein band on SDS polyacrylamide gel electrophoresis. 2) The subunit molecular weight of dental pulp and brain enzymes was determined to be 63,000 and 59,000, respectively. 3) Substrate inhibition of dental pulp and brain enzymes by phosphoenolpyruvate was not observed, and the relationship between reaction velocity and substrate concentration at pH 7.2 was explained by the Michaelis-Menten equation. Fructose-1,6-diphosphate had no observable effect on either enzyme. 4) Effect of amino acids on dental pulp and brain enzyme activity were examined, and no significant relationship was observed between the side chain structure of amino acids and their potency in inhibiting dental pulp and brain enzyme activity. Glutamic and aspartic acids markedly inhibited dental pulp and brain enzymes at pH 7.2. 5) Oxalate showed inhibitory activity against dental pulp and brain enzymes, and the Ki value was determined to be 50 microM and 80 microM, respectively. The inhibition of dental pulp and brain enzyme activity by oxalate was competitive with respect to phosphoenolpyruvate. 6) Both dental pulp and brain enzymes were clearly inhibited by malate at concentrations higher than 1.0 mM: 50% and 100% inhibition occurred at 2.2-2.3 mM and 3.0 mM malate, respectively.
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PMID:[Studies on pyruvate kinase from pig dental pulp and brain]. 198 6

Administration of vasopressin and glucagon evokes a transient release of Ca2+ from perfused livers. The Ca2+ is released from a pool that is depletable by the mitochondrial uncoupler carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP). Therefore, the mechanism of the FCCP-stimulated Ca2+ release was examined. The FCCP-stimulated Ca2+ release was associated with a decrease in ATP levels. In the presence of oligomycin, which blocked the FCCP-induced rapid ATP breakdown, FCCP did not release Ca2+ though it still stimulated respiration. The possibility that FCCP might indirectly cause a release of Ca2+ by lowering hepatic ATP was examined at two levels of organization: 1) in the whole organ, by perfusing livers with fructose, a compound that was shown previously to drastically lower ATP in the liver, and 2) in isolated microsomal vesicles by depleting ATP with glucose and hexokinase. Fructose evoked Ca2+ release from the perfused liver. Similarly, depletion of ATP by the addition of glucose and hexokinase evoked a rapid release of the accumulated Ca2+ from microsomal vesicles probably by the inhibition of the Ca2(+)-ATPase. These results demonstrate that the major mechanism by which FCCP releases Ca2+ in intact cells is by lowering ATP levels.
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PMID:Hormonal stimulation of Ca2+ release from the perfused liver: effects of uncoupler. 210 59

The glycolytic enzyme 6-phosphofructokinase (EC 2.7.1.11) was studied in adult and fetal type II pneumocytes which had been isolated from rat lung at different days of development. In addition, the activities of the enzymes hexokinase (EC 2.7.1.1), enolase (EC 4.2.1.11) and pyruvate kinase (EC 2.7.1.40) were assayed. The specific activities of the latter enzymes decrease during perinatal development and reach about adult values shortly after birth. In contrast, 6-phosphofructokinase activity increases slightly until 2 days before birth, and drops sharply afterwards. The 6-phosphofructokinase subunit composition was determined in fetal and adult type II cells. The ratio of the three subunits of 6-phosphofructokinase in type II cells isolated on fetal days 19 and 21 (term is at day 22) and in adult type II cells was identical: the three subunits were present in a ratio of 68: 14: 18 for types L, M and C, respectively. In addition, we investigated some regulatory properties of 6-phosphofructokinase from alveolar type II cells. 6-Phosphofructokinase from alveolar type II cells is strongly inhibited by increasing MgATP concentrations. This inhibition is reflected by an increase in the S0.5 for fructose 6-phosphate. Fructose 2,6-bisphosphate stimulates alveolar type II 6-phosphofructokinase. Half-maximal stimulation occurs at 1.6 and 2.0 microM fructose 2,6-bisphosphate for fetal and adult type II cells, respectively. The level of the most potent positive effector of 6-phosphofructokinase, fructose 2,6-bisphosphate, was also determined. The level of the hexose bisphosphate decreases during prenatal development; however, the level in the adult type II cells is considerably lower. The concentration of fructose 2,6-bisphosphate appears to be sufficient to fully activate 6-phosphofructokinase both in fetal and adult type II cells.
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PMID:Phosphofructokinase in alveolar type II cells isolated from fetal and adult rat lung. 252 36

Whereas glucose is a major substrate for pulmonary lipid synthesis, fructose has also been suggested as a potential substrate. In vivo pulmonary fatty acid synthesis is depressed in hormonally deprived conditions, such as diabetes, and this can be modified by fructose feeding, but not by glucose feeding. In this study the glucose and fructose utilizations were compared in normal, diabetic and fasting states using isolated perfused rat lungs. When (U-14C)- or (5-3H)-glucose was used as substrate, glucose utilization by lung was reduced by 50% in both the fasting and diabetic animals compared to the normal controls. Using (U-14C)-glucose as substrate, the incorporation of (14C)-label in various metabolites of glucose was significantly depressed. For example, this reduction was 50% in lactate, pyruvate and CO2, 15% in ethanol-insoluble fraction, 65% in neutral lipids, 75% in phospholipids, 80% in fatty acid moiety, 40% in deacylated fraction and 10% in the polysaccharide fractions. Refeeding the fasted animals or insulin treatment to the diabetic animals restored these depressed (14C)-recoveries to the normal levels. Fructose utilization was less than 10% of glucose utilization, but remained unaffected by fasting and diabetic states. In addition, pulmonary hexokinase enzyme activity was lowered significantly in fasting and diabetic animals, whereas fructokinase enzyme activity was not altered. Despite the low rate of fructose utilization, these results suggest that fructose may serve as an alternative substrate for pulmonary phospholipid synthesis when glucose utilization is significantly depressed.
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PMID:Nutritional and hormonal control of glucose and fructose utilization by lung. 390 22

Pathways of mannitol biosynthesis and utilization in Aspergillus candidus NRRL 305 were studied in cell-free extracts of washed mycelia prepared by sonic and French pressure cell treatments. A nicotinamide adenine dinucleotide-linked mannitol-1-phosphate (M1P) dehydrogenase was found in French pressure cell extracts of d-glucose-grown cells, whereas a specific mannitol-1-phosphatase was present in extracts prepared by both methods. The existence of these two enzymes indicated that mannitol may be synthesized in this organism by the reduction of fructose-6-phosphate. A specific nicotinamide adenine dinucleotide phosphate-linked mannitol dehydrogenase was also identified in both extracts. This enzyme may have been involved in mannitol utilization. However, the level of the mannitol dehydrogenase appeared to be substantially reduced in extracts from mannitol-grown cells, whereas the level of M1P dehydrogenase was increased. A hexokinase has been identified in this organism. Fructose-6-phosphatase, glucose isomerase, and mannitol kinase could not be demonstrated.
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PMID:D-mannitol metabolism by Aspergillus candidus. 430 50

1. The maximum catalytic activities of fructose diphosphatase from flight muscles of bumble-bees (Bombus spp.) are at least 30-fold those reported for the enzyme from other tissues. The maximum activity of fructose diphosphatase in the flight muscle of any particular bee is similar to that of phosphofructokinase in the same muscle, and the activity of hexokinase is similar to or greater than the activity of phosphofructokinase. There is no detectable activity of glucose 6-phosphatase and only a very low activity of glucose 6-phosphate dehydrogenase in these muscles. The activities of both fructose diphosphatase and phosphofructokinase vary inversely with the body weight of the bee, whereas that of hexokinase is relatively constant. 2. There is no significant hydrolysis of fructose 1-phosphate, fructose 6-phosphate, glucose 1,6-diphosphate and glycerol 3-phosphate by extracts of bumble-bee flight muscle. 3. Fructose 1,6-diphosphatase from bumble-bee flight muscle and from other muscles is inhibited by Mn(2+) and univalent cations; the potency of inhibition by the latter varies in the order Li(+)>Na(+)>K(+). However, the fructose diphosphatase from bumble-bee flight muscle is different from the enzyme from other tissues in that it is not inhibited by AMP. 4. The contents of ATP, hexose monophosphates, fructose diphosphate and triose phosphates in bumble-bee flight muscle showed no significant changes between rest and flight. 5. It is proposed that both fructose diphosphatase and phosphofructokinase are simultaneously active and catalyse a cycle between fructose 6-phosphate and fructose diphosphate in resting bumble-bee flight muscle. Such a cycle would produce continuous hydrolysis of ATP, with the release of energy as heat, which would help to maintain the thoracic temperature during rest periods at a level adequate for flight.
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PMID:The activities of fructose diphosphatase in flight muscles from the bumble-bee and the role of this enzyme in heat generation. 434 71

The activities of various ammoniagenic, gluconeogenic, and glycolytic enzymes were measured in the renal cortex and also in the liver of rats made diabetic with streptozotocin. Five groups of animals were studied: normal, normoglycemic diabetic (insulin therapy), hyperglycemic, ketoacidotic, and ammonium chloride treated rats. Glutaminase I, glutamate dehydrogenase, glutamine synthetase, phosphoenolpyruvate carboxykinase (PEPCK), hexokinase, phosphofructokinase, fructose-1,6-diphosphatase, malate dehydrogenase, malic enzyme, and lactate dehydrogenase were measured. Renal glutaminase I activity rose during ketoacidosis and ammonium chloride acidosis. Glutamate dehydrogenase in the kidney rose only in ammonium chloride treated animals. Glutamine synthetase showed no particular variation. PEPCK rose in diabetic hyperglycemic animals and more so during ketoacidosis and ammonium chloride acidosis. It also rose in the liver of the diabetic animals. Hexokinase activity in the kidney rose in diabetic insulin-treated normoglycemic rats and also during ketoacidosis. The same pattern was observed in the liver of these diabetic rats. Renal and hepatic phosphofructokinase activities were elevated in all groups of experimental animals. Fructose-1,6-diphosphatase and malate dehydrogenase did not vary significantly in the kidney and the liver. Malic enzyme was lower in the kidney and liver of the hyperglycemic diabetic animals and also in the liver of the ketoacidotic rats. Lactate dehydrogenase fell slightly in the liver of diabetic hyperglycemic and NH4Cl acidotic animals. The present study indicates that glutaminase I is associated with the first step of increased renal ammoniagenesis during ketoacidosis. PEPCK activity is influenced both by hyperglycemia and ketoacidosis, acidosis playing an additional role. Insulin appears to prevent renal gluconeogenesis and to favour glycolysis. The latter would seem to remain operative in hyperglycemic and ketoacidotic diabetic animals.
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PMID:Renal enzymes during experimental diabetes mellitus in the rat. Role of insulin, carbohydrate metabolism, and ketoacidosis. 623 75


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