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)

The effect of dietary and hormonal variations on the specific activities of hexokinase isoenzymes, N-acetylglucosamine kinase and pyruvate kinase isoenzymes in parenchymal and non-parenchymal liver cells was studied. Hexokinase D was markedly decreased in hepatocytes from animals fasted or fed on the carbohydrate-free diet as well as from diabetic rats, attaining a constant low level of about 17% of normal values. Pyruvate kinase L was also diminished in hepatocytes under the same experimental conditions. In contrast, the three high-affinity hexokinase isoenzymes A, B and C remained without variation in total amount or in their relative proportions in hepatocytes and non-parenchymal liver cells isolated from animals under the various conditions studied. N-Acetylglucosamine kinase activities also did not change either in parenchymal or in non-parenchymal liver cells under all conditions. The results are discussed in relation to the significance of N-acetylglucosamine kinase and the various hexokinase isoenzymes for the phosphorylation of glucose after dietary and hormonal manipulations.
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PMID:Stability of hexokinases A, B and C and N-acetylglucosamine kinase in liver cells isolated from rats submitted to diabetes and several dietary conditions. 608 34

The kinetic properties of the glycosomal hexokinase (HG)2 and phosphofructokinase (PFK) from Trypanosoma brucei bloodstream forms were investigated. Hexokinase has a very high affinity for glucose (Km = 17 microM) and exhibits a broad pH optimum with a maximum at pH 7.8. No indications have been found for regulation of HK activity. Phosphofructokinase behaves as an allosteric protein with respect to its substrate, fructose-6-phosphate. 5'-AMP acts as a positive allosteric effector. The apparent Km for 5'-AMP is extremely low (7 microM). The other substrate for PFK is Mg2+-ATP chelate which activates the enzyme in a hyperbolic manner. Excess of ATP over Mg2+ is inhibitory. The enzyme needs Mg2+ for full activity. Compounds known to be positive or negative heterotrophic modifiers of PFK in other organisms are without effect. It is concluded that PFK and HK probably do not play a regulatory role in glycolysis in T. brucei.
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PMID:Regulation of glycolysis in Trypanosoma brucei: hexokinase and phosphofructokinase activity. 612 64

Hexokinase variation in insects appears to be under the control of a single locus in some species and under multiple-locus control in others. It is often difficult to distinguish the number of loci controlling hexokinase expression. Analysis of hexokinase electrophoretic patterns in six species of mosquitoes and five species of crickets, as well as a review of hexokinase variation in other insect species, is used to emphasize the importance of interspecific comparisons when making genetic inferences. Evidence is provided which adds support for multiple hexokinase loci in dipterans. Hexokinase control by multiple loci may be difficult to determine in some species because of tight linkage, disequilibrium, and/or posttranslational modification.
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PMID:Genetic control of hexokinase variation in insects. 612 38

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

Hexokinase (ATP: hexose 6-phosphotransferase, E.C.2.7.1.1) and phosphofructokinase (ATP:fructose-6-phosphate 1-phosphotransferase, E.C.2.7.1.11), two key regulatory enzymes of the glycolytic pathway in vertebrate cells, have been isolated and partially purified from Trypanosoma (Schizotrypanum) cruzi epimastigotes. Both enzymes are associated with particles sedimentable at 105 000 X gav for 1 h and have a high degree of latency; they can be solubilized by sonication. Hexokinase catalyses the phosphorylation of a series of monosaccharides at the following relative rates: D-glucose (100) congruent to D-fructose (97) greater than 2-deoxy-D-glucose (72) congruent to mannose (69) greater than 2-amino-D-glucose (63) greater than 3-O-methyl-D-glucose (21). Very little or no phosphorylating activity was found for D-galactose, N-acetyl-2-amino-D-glucose or 1-alpha-methyl-D-glucose. D-Glucose phosphorylation at fixed ATP concentration follows simple Michaelis-Menten kinetics with Km = 40 microM and Vmax = 440 nmol min-1 mg-1 protein. D-Mannose, 2-deoxy-D-glucose and N-acetyl-2-amino-D-glucose act as competitive inhibitors of glucose phosphorylation, suggesting a single kinase. Mg2+-ATP is the preferred phosphoryl donor, ITP and GTP being much less effective. T. cruzi hexokinase is not inhibited by D-glucose 6-phosphate, or by any of the following compounds (2 mM):D-fructose 6-phosphate, D-fructose 1,6-diphosphate, D-glucose 1,6-diphosphate, phosphoenol pyruvate, L-malate and citrate. Phosphofructokinase displays simple Michaelis-Menten kinetics with no evidence of sigmoidicity with respect to D-fructose 6-phosphate at all ATP concentrations tested, giving a Km of 1.31 mM and Vmax = 400 nmol min-1 mg-1 protein at optimal ATP levels. With respect to ATP, the enzyme exhibits Michaelis-Menten kinetics at low concentration (less than 1 mM) of the substrate (Km = 40 microM at 5 mM MgCl2, pH 7.4). A moderate inhibition is observed at high ATP levels (70% of maximal activity at 2 mM). GTP can substitute for ATP as the phosphoryl donor (Km = 79 microM under the same conditions), but produces only very small inhibitory effects at high concentrations. 5'-AMP activates the enzyme by decreasing its Km with respect to D-fructose 6-phosphate without affecting Vm. Other well-known regulators of the activity of this enzyme in procaryote and vertebrate systems such as citrate, phosphoenol pyruvate, ammonium and phosphate ions have no effect in T. cruzi.
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PMID:Regulation of energy metabolism in Trypanosoma (Schizotrypanum) cruzi epimastigotes. I. Hexokinase and phosphofructokinase. 623 52

Mitochondria were isolated from whole homogenates of normal liver and Novikoff hepatomas using reorienting rate zonal centrifugation on sucrose gradients. The activities of several mitochondrial-specific enzymes and ultrastructure were compared in the two tissues. Our results indicate that cytochrome oxidase, lipoamide dehydrogenase, malate dehydrogenase, and succinate dehydrogenase activities are all higher in liver homogenates than in Novikoff hepatoma homogenates. Mitochondrial hexokinase, however, is much greater in the hepatoma than in liver. The activity of these enzymes in isolated mitochondria displayed a much different pattern. Both cytochrome oxidase and succinate dehydrogenase activities were higher in hepatoma mitochondria than in liver mitochondria. Lipoamide dehydrogenase and malate dehydrogenase, conversely, were higher in liver mitochondria. Hexokinase was found to be virtually absent in liver mitochondria but plentiful in hepatoma mitochondria. Ultrastructural studies have shown that the hepatoma mitochondria are much smaller in size, which results in a decreased rate of migration into the gradient. These studies have also shown that normal liver consists of predominantly "condensed" forms of mitochondria, whereas hepatoma contained a majority of "twisted" species. Experiments using 1% bovine serum albumin in the homogenization procedures and in the gradient have confirmed earlier observations that bovine serum albumin is essential for optimal isolation of neoplastic mitochondria.
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PMID:Characteristics of mitochondria isolated by rate zonal centrifugation from normal liver and Novikoff hepatomas. 624 94

The activities of hexokinase, glucose-6-phosphate dehydrogenase, hydroxyacyl-CoA-dehydrogenase, adenylate kinase and glutathione reductase were determined in the aorta of rats made diabetics with streptozotocin for over two weeks and in noninjected controls. Adenosinetriphosphate (ATP) and total adenine nucleotide content were also measured. Glutathione reductase activity was not significantly changed in the diabetic aorta whereas the activities of glucose-6-phosphate dehydrogenase, hydroxyacyl-CoA-dehydrogenase and adenylate kinase were all increased. Hexokinase activity was significantly decreased in diabetic rat aorta. When measured after incubation in vitro for 2 h with 5.6 mmol/l glucose, the ATP-concentration was reduced in the diabetic aorta while the total concentration of adenine nucleotides was unchanged. Insulin treatment started three days after induction of diabetes with streptozotocin and continued for twelve days restored the growth rate of the rats but their glucose metabolism was not completely normalized. After insulin treatment no significant differences between diabetic and normal rats were found in the aortic activities of glucose-6-phosphate dehydrogenase, hydroxyacyl-CoA-dehydrogenase, adenylate kinase or in the ATP content.
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PMID:Influence of diabetes on enzyme activities in rat aorta. 626 26

Hexokinase-binding protein and mitochondrial porin were isolated from rat liver mitochondria by different procedures. It was found that the hexokinase-binding protein made lipid vesicles permeable to ADP and formed asymmetric pores in lipid bilayer membranes identical to those obtained from the mitochondrial porin. On the other hand, the mitochondrial porin confers the ability to bind hexokinase. In addition, evidence is presented that both hexokinase-binding protein and mitochondrial porin bind glycerol kinase.
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PMID:Evidence for identity between the hexokinase-binding protein and the mitochondrial porin in the outer membrane of rat liver mitochondria. 628 67

Due to the close correlation between glucose mobilization and utilization within animal tissues, in this paper, the stages of appearance of phosphorylase, glucose-6-phosphatase and hexokinase as well as the levels of some intermediates of glucose metabolism have been investigated during Bufo bufo development. Phosphorylase first appears at stage 13 and is dominant in the neural part of the embryo, but, after this stage, increases relatively more in the nonneural one. Hexokinase appears at stage 17 and glucose-6-phosphatase soon after. Phosphorylase appearance at stage 13 is correlated with an increase of lactate content in the embryo; this may indicate a metabolization of hexoses. On this basis, the subsequent appearance of hexokinase and glucose-6-phosphatase activities also seems coherent with hexose mobilization and utilization within embryo. No direct causative factor for the changes observed was evident.
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PMID:Developmental aspects of hexose metabolism in Bufo bufo. 629 68

The relative contributions of transport and intracellular metabolism of glucose to the control of overall glucose utilization were evaluated in rat adipocytes. Transport of 3-O-methylglucose and hexokinase activity in crude homogenates were measured and the derived kinetic parameters incorporated into network thermodynamic computer simulations. Hexokinase was found to be inhibited in a fully noncompetitive pattern by glucose 6-phosphate (Ki = 0.46 mM). When this feature was incorporated into the computer simulations, they reflected measured rates of overall glucose utilization as well as intracellular glucose 6-phosphate concentrations, both in the presence and absence of insulin. The effect of the hormone was represented in the simulations solely by an increase in the number of hexose carriers. A predominant stimulation of transport rather than metabolism was also suggested by the finding that intracellular glucose concentrations assessed by glucose-induced 3-O-methylglucose counter-transport were higher in the presence than in the absence of insulin over a wide range of extracellular glucose concentrations. Nevertheless, it was also found that insulin induced a significant countertransport gradient while the oxidant H2O2 did not, which suggests that insulin-stimulated metabolism does increase overall glucose utilization independently of effects on transport. These studies show that the kinetic patterns of basal and insulin-stimulated glucose utilization in adipocytes may be generated simply by coupling transport and phosphorylation steps and providing for inhibition of the latter by accumulated glucose 6-phosphate.
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PMID:Glucose utilization in rat adipocytes. The interaction of transport and metabolism as affected by insulin. 633 5


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