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)

During steady-state, the Pi released in the medium is derived from glucose-6-phosphate which continuously regenerates the ATP hydrolyzed. A membrane potential (delta psi) can be built up in submitochondrial particles using glucose-6-phosphate and hexokinase as an ATP-regenerating system. The energy derived from the membrane potential thus formed, can be used to promote the energy-dependent transhydrogenation from NADH to NADP+ and the uphill electron transfer from succinate to NAD+. In spite of the large differences in the energies of hydrolysis of ATP (delta G degrees = -7.0 to -9.0 kcal/mol) and of glucose-6-phosphate (delta G degrees = -2.5 kcal/mol), the same ratio between Pi production and either NADPH or NADH formation were measured regardless of whether millimolar concentrations of ATP or a mixture of ADP, glucose-6-phosphate and hexokinase were used. Rat liver mitochondria were able to accumulate Ca2+ when incubated in a medium containing hexokinase, ADP and glucose-6-phosphate. The different reaction measured with the use of glucose-6-phosphate and hexokinase were inhibited by glucose concentrations varying from 0.2 to 2 mM. Glucose shifts the equilibrium of the reaction towards glucose-6-phosphate formation thus leading to a decrease of the ATP concentration in the medium.
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PMID:Reversal of oxidative phosphorylation in submitochondrial particles using glucose 6-phosphate and hexokinase as an ATP regenerating system. 149 30

Polyphosphate glucokinase (EC 2.7.1.63, polyphosphate:glucose phosphotransferase) was covalently coupled to collagen-coated silica gel beads. The immobilized enzyme, as a packed-bed reactor, was used to determine glucose in serum and other samples. The method was based on a spectrophotometric measurement of NADPH produced by two consecutive reactions, similar to the hexokinase method. The described approach takes advantage of the greater stability of polyphosphate compared to that of ATP, the greater specificity of polyphosphate glucokinase versus that of hexokinase, and the reusability of the immobilized enzyme. Linearity, precision, and accuracy of the method were tested and found to be very good. The results were linear between 10 and 50 nmol of glucose in a 50-microliter sample and the coefficient of variation was less than 4% in five successive determinations. The recovery of glucose was about 100% after calibration of the method. The results of the measurements correlated well with those obtained with soluble polyphosphate glucokinase (r = 0.997, y = 1.036x - 0.016). The immobilized-enzyme reactor showed good operational stability during a month of use, losing about 12% of its initial activity.
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PMID:Glucose determination using immobilized polyphosphate glucokinase. 166 65

ATP is known to be easily determined fluorometrically after it is utilized to produce the corresponding amount of NADPH by combined reactions of hexokinase and glucose-6-phosphate dehydrogenase. We studied further whether nucleoside triphosphates other than ATP can be also determined in a similar manner if they were incubated for a longer period with an increased amount of hexokinase. It was shown that CTP, GTP, ITP, and UTP can be utilized to produce the corresponding amount of NADPH after an incubation of at least 60 min and that 0 to 50 nmols of these nucleotides were able to be determined fluorometrically.
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PMID:Determination of nucleoside triphosphates by use of combined reactions of hexokinase and glucose-6-phosphate dehydrogenase. 181 Feb 51

Rats bearing the Walker-256 carcinosarcoma have a profoundly altered liver metabolite content with significant increases in the concentrations of glucose 6-phosphate, fructose 1,6-bisphosphate, citrate, lactate, and alanine, while the concentrations of glucose, pyruvate, dihydroxyacetone phosphate, and glutamine are decreased. As a result of these changes both the cytosolic NAD+/NADH ratio and the cytosolic phosphorylation potential are significantly lowered while no changes are detected in either the cytosolic NADP+/NADPH ratio or the mitochondrial NAD+/NADH ratio. These hepatic changes are accompanied by marked increases in the circulating concentrations of lactate, non-esterified fatty acids, and triacylglycerols. The activities of both liver hexokinase and phosphofructokinase are also significantly elevated in the tumor-bearing rats. The changes observed both in the redox state and phosphorylation potential are in agreement with the energy imbalance associated with tumor burden.
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PMID:The energy state of tumor-bearing rats. 199 70

A method to monitor extracellular glucose in freely moving rats, based on intracerebral microdialysis coupled to an enzyme reactor is described. The dialysate is continuously mixed with a solution containing the enzymes hexokinase and glucose-6-phosphate dehydrogenase, and the fluorescence of NADPH formed enables the on-line registration of extracellular glucose. The method is applied to monitor changes in extracellular brain glucose during the infusion of glucose, electrically induced seizure, immobilization stress, and repetitive hypoxia. After glucose loading or after seizure, hippocampus dialysate glucose concentration was increased transiently. During immobilization, there was a short-lasting decrease and, thereafter, an increase in the extracellular hippocampus glucose. During repetitive hypoxia in rats with a unilaterally occluded carotid artery, the content of glucose of striatal dialysates followed closely changes in blood pressure. These results illustrate the usefulness of the method in studying changes in brain glucose concentrations under pathological and physiological conditions.
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PMID:On-line monitoring of extracellular brain glucose using microdialysis and a NADPH-linked enzymatic assay. 207 9

The rate of ATP formation from ADP by adenylate kinase is known to be easily followed by determination of the increase in fluorescence due to the NADPH that is formed by combined reactions of hexokinase and gluc-6-p dehydrogenase. We found that the rate of CTP formation from CDP also can be followed similarly by use of more units of hexokinase and extension of the reaction time. A crude enzyme sample containing most of the activity of adenylate kinase was prepared from pig brain and eluted from a CM-cellulose column. Enzymatic activity of ATP formation and that of CTP formation were compared for all the fractions. Two fractions were found in the eluate; one was rather specific for ADP as substrate, and the other was less specific for ADP and could form CTP at an appreciable rate.
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PMID:Multiple forms of adenylate kinase in pig brain. 224 94

Selected aspects of the metabolism of Plasmodium falciparum are reviewed, but conclusions based on the study of other species of plasmodia are intentionally not included since these may not be applicable. The parasites increase glucose consumption 50-100 fold as compared to uninfected red cells; most of the glucose is metabolized to lactic acid. The parasite contains a complete set of glycolytic enzymes. Some enzymes such a hexokinase, enolase and pyruvate kinase are vastly increased over corresponding levels in uninfected red cells. However, the pathway for synthesizing 2,3-diphosphoglycerate (2,3-DPG) is absent. Parasitized red cells show a decline in the concentration of 2,3-DPG which may function as an inhibitor for certain essential enzyme pathways. Pentose shunt activity is increased in absolute terms, but as a percent of total glucose consumption, there is a decrease during parasite infection of the red cell. The parasite contains a gene for G6PD and can produce a small quantity of parasite-encoded enzyme. It is not clear if the production of this enzyme can be up-regulated in G6PG deficient host red cells. The NADPH normally produced by the pentose shunt can be obtained from other parasite pathways (such as glutamate dehydrogenase). NADPH may subserve additional needs in the infected red cell such as driving diribonucleotide reductase activity--a rate limiting enzyme in DNA synthesis. The role of NADPH in protecting the parasite-red cell system against oxidative stress (via glutathione reduction) remains controversial. Parasitized red cells contain about 10 times more NAD(H) than uninfected red cells, but the NADP(H) content is unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Plasmodium falciparum carbohydrate metabolism: a connection between host cell and parasite. 225 22

Chemiluminometric methods are described for the automated flow injection analysis of NADPH and NADH using an immobilized enzyme column reactor and serum magnesium. This application is for the clinical analysis of NADPH and NADH. The reactor for NADPH and NADH contains immobilized L-glutamate dehydrogenase and L-glutamate oxidase, and that for serum magnesium immobilized hexokinase, glucose-6-phosphate dehydrogenase, L-glutamate dehydrogenase and L-glutamate oxidase. When the sample is introduced into the four-enzyme bioreactor, hydrogen peroxide is produced in proportion to the concentration of serum magnesium by the successive reactions. A co-immobilized hexokinase/glucose-6-phosphate dehydrogenase/glutamate dehydrogenase column reactor gave better efficiency compared with an enzyme column which was prepared by packing co-immobilized hexokinase/glucose-6-phosphate dehydrogenase and immobilized glutamate dehydrogenase to make two layers. Magnesium in serum was determined with 1 microL of the sample without carry-over and for an assay time of approximately 15 s. The present method is sensitive (detection limit 0.1 nmol) because Mg2+ is recycled in a column, and gives perfect linearity of the data up to 3.0 mmol/L with satisfactory precision, reproducibility, and accurate reaction recoveries.
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PMID:A chemiluminometric method for NADPH and NADH using a two-enzyme bioreactor and its application to the determination of magnesium in serum. 238 94

The primary cause of red cell destruction in enzymopathies of anaerobic remains controversial and difficult to investigate especially because the erythrocyte population in enzymopenic patients is largely heterogeneous. We have shown that loading human erythrocytes with monospecific enzyme-inactivating antibodies could be useful in understanding the biochemical modifications occurring in enzymopenic erythrocytes and the mechanisms leading to red cell destruction. Hexokinase-inactivating antibodies were prepared and loaded in human erythrocytes using a procedure of encapsulation based on hypotonic hemolysis, isotonic resealing and reannealing. Red blood cells loaded with anti-hexokinase IgG showed 20 +/- 3% residual hexokinase activity while all other enzymes were normal. Lactate production by these cells was 30% of controls while the amount of glucose metabolized in the hexose monophosphate pathway (HMP) was unchanged under resting conditions. However, in the presence of methylene blue HMP rates were only 12% of controls. Determination of adenine nucleotide levels suggests that the antihexokinase-loaded red blood cells are not able to maintain, in vitro, their ATP level as well as their 2,3-diphosphoglycerate. Osmotic fragility, methemoglobin, and reduced glutathione content were near normal. These and other properties of the antihexokinase-loaded erythrocytes were similar to those found in cases of hexokinase deficiency. When the antibody-loaded erythrocytes were chromatrographed on immobilized Protein A columns 66-70% of cells were retained by the column against 0-10% of controls suggesting that hexokinase inactivation promotes autologous IgG binding. Since the phenomenon is known to be associated with red cell phagocytosis, it could be concluded that in hexokinase deficiency red cells are mainly removed by phagocytosis, and that hemolysis probably occurs in cases of oxidative stress when the production of a large amount of reducing equivalents (NADPH) is needed but not provided by the hexokinase-deficient erythrocytes.
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PMID:Human red blood cell loading with hexokinase-inactivating antibodies. An in vitro model for enzyme deficiencies. 250 71

A histochemical analysis of reaction rates of a series of enzymes was performed in electromotor neurons of the weakly electric fish Apteronotus leptorhynchus. These neurons were selected because of their functional homogeneity. The high metabolic activity of these cells as well as their large size facilitate cytophotometric analysis in cryostat sections. Sections were incubated for the activity of hexokinase, glucose-6-phosphate dehydrogenase, succinate dehydrogenase, NADPH dehydrogenase, NADPH ferrihaemoprotein reductase and beta-hydroxybutyrate dehydrogenase. All media contained polyvinyl alcohol as tissue stabilizer and Nitro BT as final electron acceptor. Measurements were performed with a Vickers M85a cytophotometer. Linear relationships between the specific formation of formazan (test minus control reaction) and incubation time were obtained for all enzymes although some reactions showed an initial lag phase or an intercept with the ordinate. The relatively high activities of hexokinase, succinate dehydrogenase and the extremely low activity of hydroxybutyrate dehydrogenase indicate that energy is mainly supplied by glycolysis. Glucose-6-phosphate dehydrogenase showed a high activity whereas NADPH reductase and dehydrogenase activity were low in electromotor neurons, indicating that the NADPH generated is largely used for biosynthesis. Despite their synchronous firing pattern activity, electromotor neurons showed a considerable heterogeneity with respect to their metabolic activity.
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PMID:Enzyme reaction rate studies in electromotor neurons of the weakly electric fish Apteronotus leptorhynchus. 251 71


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