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)

The natural product of the glucose-6-phosphate dehydrogenase reaction is 6-phosphoglucono-delta-lactone, which must be hydrolyzed to 6-phosphogluconic acid before it can be further metabolized by 6-phosphogluconate dehydrogenase. Because this lactone is very unstable, it has been uncertain whether the enzyme that hydrolyzes it, 6-phosphogluconolactonase, is required for functioning of the hexose monophosphate pathway. We have purified glucose-6-phosphate dehydrogenase, 6-phosphogluconolactonase, and 6-phosphogluconate dehydrogenase from human erythrocytes to the point where each enzyme is essentially free of each of the other activities. We constructed an artificial hexose monophosphate pathway from these enzymes, providing as substrate 14C-labeled glucose-6-phosphate either directly or by continual generation from 14C-glucose by yeast hexokinase and adenosine triphosphate. The oxidation of 6-phosphogluconic acid was estimated by measuring the CO2 formed. In the absence of a reduced nicotinamide-adenine dinucleotide phosphate (NADPH)-oxidizing system, such as oxidized glutathione (GSSG)-glutathione reductase or phenazine methosulfate, little CO2 was formed, and the presence of 6-phosphogluconolactonase did not affect the amount that was produced. When the hexose monophosphate pathway was stimulated by providing an NADPH-oxidizing system, CO2 was produced two and a half to five times as fast in the presence of 6-phosphogluconolactonase as in its absence. These studies suggest that 6-phosphogluconolactonase is required for the functioning of the hexose monophosphate pathway when the rate of oxidation of NADPH is accelerated.
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PMID:Limiting role of 6-phosphogluconolactonase in erythrocyte hexose monophosphate pathway metabolism. 393 73

The phosphorylation of D-glucose (1.0mM) was measured in homogenates of tumoral islet cells incubated at 7 degrees C in the presence of labelled alpha- and/or beta-D-glucose, with or without exogenous glucose 6-phosphate. The close-to-maximal reaction velocity of hexokinase was higher with beta- than alpha-D-glucose. The latter anomer inhibited beta-D-glucose phosphorylation more than the beta-anomer decreased the phosphorylation of alpha-D-glucose. This behaviour was accounted for by the higher affinity of hexokinase for alpha- than for beta-D-glucose. These direct measurements of the relative contribution of each anomer to the overall rate of glucose phosphorylation in the presence of mixed populations of alpha- and beta-D-glucose validate the concept that the phosphorylation of D-glucose displays anomeric specificity even when the hexose is used at anomeric equilibrium. Glucose 6-phosphate inhibited the phosphorylation of the two anomers more severely when alpha-D-glucose rather than beta-D-glucose was the most abundant anomer.
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PMID:Reciprocal influence of glucose anomers upon their respective phosphorylation by hexokinase. 395 89

Enzymatic assays were modified to permit sensitive and highly reproducible simultaneous measurements of D-mannose and D-glucose in biological fluids during weeks 34-40 of human pregnancy. Plasma mannose and glucose averaged 9.8 +/- 0.4 (+/- SEM) and 790 +/- 16 micrograms/ml, respectively, after an overnight fast in pregnant women (n = 22) with normal carbohydrate metabolism. Significantly higher plasma mannose levels were found, despite only minor increases in plasma glucose, in pregnant women with relatively well controlled diabetes mellitus after an overnight fast (16.9 +/- 0.6 micrograms/ml mannose; 883 +/- 29 micrograms/ml glucose; n = 31) or 3-4 h after breakfast (15.7 +/- 1.2 micrograms/ml mannose; 1159 +/- 101 micrograms/ml glucose; n = 19). Plasma mannose correlated significantly with plasma glucose in the women with diabetes mellitus, particularly after an overnight fast. Samples of amniotic fluid were also obtained from the gravida with diabetes mellitus to provide some index of simultaneous relationships in utero. Amniotic fluid mannose and glucose averaged 5.9 +/- 0.4 and 302 +/- 24 micrograms/ml, respectively, after an overnight fast and 6.7 +/- 1.3 and 459 +/- 84 micrograms/ml 3-4 h after breakfast. In amniotic fluid, as in plasma, the concurrent levels of mannose and glucose conformed to relatively fixed relationships. Thus, both fetus and mother appear to be exposed to readily demonstrable amounts of mannose during late gestation and the absolute as well as relative abundance of mannose may be increased coincident with faulty maternal glucoregulation. However, since mannose did not exceed 3% of the concurrent concentration of glucose in any instance, it does not seem likely that endogenous levels of circulating mannose can modify glucose utilization appreciably by competing with glucose for phosphorylation via hexokinase and subsequent intracellular processing.
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PMID:Relationships between glucose and mannose during late gestation in normal pregnancy and pregnancy complicated by diabetes mellitus: concurrent concentrations in maternal plasma and amniotic fluid. 395 33

At the second and third trimesters of pregnancy an increase in activity of hexokinase, glucose-6-phosphate-(G6PD) and 6-phosphogluconate dehydrogenases (6-PDG) occurred simultaneously with a decrease in concentrations of NADPH2 by 26%, ATP by 17% and an increase in NADP by 10-15% in the pregnant women. Total amount of nicotinamide adenine dinucleotide phosphate was unaltered and constituted 0.082-0.075 mmole/L in erythrocytes from both pregnant and nonpregnant women. Activities of hexose monophosphate and glycolytic pathways of glucose metabolism appear to increase in erythrocytes under conditions of normal pregnancy. Concentration of oxidized glutathione tended to increase in the pregnant women, suggesting a possibility of the hexose monophosphate shunt activation.
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PMID:[Pentose monophoshate pathway and the glutathione system in physiological pregnancy]. 400 57

A study of the reverse reaction of rat brain hexokinase (ATP:D-hexose 6-phosphotransferase, EC 2.7.1.1) has been performed using a photometric method based on a mutarotase-glucose oxidase-peroxidase-chromogen system to trap and visualize glucose, plus a glycerol kinase-glycerol system to trap ATP. Glucose 6-phosphate or 2-deoxyglucose 6-phosphate were used as phosphoryl donors at different concentrations of ADP. Variation of glucose 6-phosphate concentrations resulted in a biphasic curve from which apparent Km and Ki values of ca. 0.2 mM were calculated. In contrast, variation of 2-deoxyglucose 6-phosphate concentrations resulted in Michaelian kinetics with an apparent Km of 2 mM. The Km value for MgADP was 16 mM irrespective of the nature and concentration of the hexose 6-phosphate substrate. These results are fully consistent with an allosteric site for glucose 6-phosphate as an explanation for the inhibition of animal hexokinases by glucose 6-P and further indicate that the maximal rate is the parameter affected. From these observations and previous knowledge, the possible occurrence in animal hexokinases of a regulatory site for ATP to account for the competition between glucose 6-phosphate and ATP in the forward reaction is postulated.
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PMID:Allosteric inhibition of brain hexokinase by glucose 6-phosphate in the reverse reaction. 400 67

The regulation of the hexose monophosphate shunt of human erythrocytes under conditions of oxidative stress has been investigated by monitoring the reduction of oxidised glutathione (GSSG) to reduced glutathione (GSH) in erythrocytes containing high levels of GSSG; 1H NMR and a biochemical assay were used to measure the changes. A reconstituted metabolic system prepared with the purified erythrocyte enzymes was used in conjunction with studies of intact cells and haemolysates to determine the dependence of the rate of GSH production on the activities of hexokinase and glucose-6-phosphate dehydrogenase. Both of these enzymes have previously been claimed to be the rate-limiting step of oxidatively stimulated flux through the hexose monophosphate shunt. The absence of a kinetic isotope effect on the rate of GSH production in these systems, when [1-2H]glucose replaced glucose as the source of reducing equivalents, showed that glucose-6-phosphate dehydrogenase activity was not a strong determinant of the flux. The dependence of the rate of GSH production on the concentration of the hexokinase inhibitors glucose 1,6-bisphosphate and glycerate 2,3-bisphosphate showed that, under conditions of oxidative stress, hexokinase was the principal determinant of flux through the shunt. Glucose 1,6-bisphosphate at the concentration present in vivo appears to be more important in limiting hexokinase activity, and thus the rate of glucose utilisation, than was previously assumed. A detailed computer model of the system was developed based on the reported kinetic parameters of the enzymes involved. A sensitivity analysis of this model predicted that the hexokinase reaction would have a sensitivity coefficient of 0.995 with respect to the maximal rate of GSH production.
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PMID:Regulation of the human-erythrocyte hexose-monophosphate shunt under conditions of oxidative stress. A study using NMR spectroscopy, a kinetic isotope effect, a reconstituted system and computer simulation. 401 89

A 27-year-old woman with severe chronic hemolytic anemia was found to have reduced red cell hexokinase activity when the degree of reticulocytosis was considered. This enzyme had normal pH-dependent activity, normal Km for glucose, fructose, and mannose, normal Km for Mg adenosine triphosphate (ATP)2- and Ki for glucose-1,6-diphosphate. Furthermore, the pH-dependence and orthophosphate dependence of Ki for glucose-1,6-diphosphate were normal. However, this hexokinase was inactivated rapidly at 44 degrees C. No abnormalities were found in the red cell hexokinase isozymic pattern when it was compared with the profile obtained from cells of similar age. The hexokinase specific activity was reduced in all the red blood cell fractions obtained by density gradient ultracentrifugation; a marked difference in the distribution of cells through the gradient was evident. Among the glycolytic intermediates, a significant decrease of 2,3-diphosphoglycerate was evident. ATP and glucose 6-phosphate were also reduced when compared with cells of similar. Glucose consumption of the hexokinase-deficient cells decreased, but the rate of glucose metabolized through the hexose monophosphate shunt was unchanged. Although the total hexokinase activity in lymphocytes was only reduced by 37%, a marked hexokinase deficiency was detected in blood platelets (20% to 25% of normal activity). The parents and one of two siblings of the patient were heterozygous for the defect, with 66% to 74% of normal erythrocyte hexokinase activity and reduced heat stability of the enzyme. These results, when compared with those obtained in previously reported cases of hexokinase deficiency, provide further evidence of the broad phenotypic variability that characterizes this disorder. Furthermore, it is suggested that failure of energy generation is probably the primary cause of hemolytic anemia in hexokinase deficiency.
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PMID:Hereditary nonspherocytic hemolytic anemia due to a new hexokinase variant with reduced stability. 402 85

A 14-month-old child who had a haemolytic episode when he was 5 years old, and with psychomotor retardation, was found to have decreased red cell hexokinase activity. The mutant enzyme was characterized by an increased affinity for glucose associated with an increased inhibition constant for glucose-1,6-diphosphate. Affinity for Mg ATP2-, heat stability and pH-optimum were normal. The isozymic pattern of the red cell enzyme was normal but all the molecular forms were present in reduced amounts. The kinetics of decay of hexokinase during cell ageing was also normal. Glucose consumption of the hexokinase deficient cells was 60-65% of the controls while the amount metabolized through the hexose monophosphate shunt was unchanged. Red cell 2,3-diphosphoglycerate and glucose-6-phosphate levels were normal in the proband but reduced in the erythrocytes of his parents, who were heterozygous for the defect but had normal haematological data. Comparison with the 13 previously reported cases of hexokinase deficiency confirms the broad phenotypic variability that characterizes this disorder.
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PMID:Human erythrocyte hexokinase deficiency: a new variant with abnormal kinetic properties. 405 30

1. The ability of exogenously administered cyclic AMP (adenosine 3':5'-monophosphate) to exert andromimetic action on certain carbohydrate-metabolizing enzymes was investigated in the rat prostate gland and seminal vesicles. 2. Cyclic AMP, when injected concurrently with theophylline, produced marked increases in hexokinase, phosphofructokinase, glyceraldehyde phosphate dehydrogenase, pyruvate kinase, and two hexose monophosphate-shunt enzymes, as well as alpha-glycerophosphate dehydrogenase activity in accessory sexual tissues of castrated rats. The 6-N,2'-O-dibutyryl analogue of cyclic AMP caused increases of enzyme activity that were greater than those induced by the parent compound. 3. Time-course studies demonstrated that, whereas significant increases in the activities of most enzymes occurred within 4h after the injection of cyclic AMP, maximal increases were attained at 16-24h. 4. Increase in the activity of the various prostatic and vesicular enzymes was dependent on the dose of cyclic AMP; in most instances, 2.5mg of the cyclic nucleotide/rat was sufficient to elicit a statistically significant response. 5. Administration of cyclic AMP and theophylline also produced stimulation of enzyme activities in secondary sexual tissues of immature rats. 6. Cyclic AMP and theophylline did not affect significantly any of the enzymes studied in hepatic tissue. 7. Stimulation of various carbohydrate-metabolizing enzymes in the prostate gland and seminal vesicles by cyclic AMP was independent of adrenal function. 8. Concurrent treatment with actinomycin or cycloheximide prevented the cyclic AMP- and theophylline-induced increases in enzyme activities in both castrated and adrenalectomized-castrated animals. 9. Administration of a single dose of testosterone propionate (5.0mg/100g) to castrated rats caused a significant increase in cyclic AMP concentration in both accessory sexual tissues. 10. In addition, treatment with theophylline potentiated the effects of a submaximal dose of testosterone (1.0mg/100g) on all those prostatic and seminal-vesicular enzymes that are increased by exogenous cyclic AMP. 11. The evidence indicates that cyclic AMP may be involved in triggering the known metabolic actions of androgens on secondary sexual tissues of the rat.
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PMID:Metabolic control mechanisms in mammalian systems. Involvement of adenosine 3':5'-cyclic monophosphate in androgen action. 411 Apr 60

The effects of exogenously administered 3',5'-monophosphate (cyclic AMP) on glycogen synthesis and hexose monophosphate shunt enzymes were studied in the uteri of immature and ovariectomized rats to determine whether cyclic AMP mimics the known effects of estrogenic hormones. The injection of cyclic AMP concurrently with theophylline, significantly increased the activity of uterine hexokinase, phosphofructokinase, pyruvate kinase, glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, and uterine glycogen content in immature rats (p less than .05). These increases were related to the dose of cyclic AMP, and as little as .2 mg was able to stimulate uterine glycogen to 169% of control values. The treatment did not significantly increase the activity of the key glycolytic or hexose monophosphate shunt enzymes in the lung and thymus, although these tissues are also not receptive to estrogen. Neither estradiol-17beta or cyclic AMP and theophylline produced any measurable effect on the uterine enzymes, isocitrate dehydrogenase, or alpha-glycerophosphate dehydrogenase. In ovariectomized and adrenalectomized-ovariectomized animals, cyclic AMP and theophylline significantly stimulated the activity of key glycolytic and hexose monophosphate shunt enzymes (p less than .05); the N6, 02-dibutyryl analog of cyclic AMP being more potent than the parent compound. Pretreatment with actinomycin or cycloheximide significantly inhibited the effects of cyclic AMP and theophylline (p less than .05), which indicates that neither cyclic AMP stimulation or the inhibition of the effects of cyclic AMP were dependent on adrenal function. The results support the possiblity that cyclic AMP may be involved in mediating the metabolic effects of estrogen on the uterus.
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PMID:Metabolic control mechanisms in mammalian systems. XV. Studies on the role of adenosine 3' ,5'-monophosphate in estrogen action on the uterus. 411 Aug 9


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