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 expression of the kinetic Hill coefficient for a two-substrate, two-product mnemonical enzyme has been derived. Its relation with the gamma coefficient, that is the slope of the reciprocal plots for 1/[A]----O, has been established. The variation of this Hill coefficient, as a function of the second substrate and product concentrations, has been studied theoretically. Whereas the gamma coefficient does not vary as a function of the substrate and first product concentrations, the kinetic Hill coefficient does. If the enzyme is positively co-operative, the Hill coefficient increases upon increasing the second substrate concentration and decreases if the first product concentration is increased. The converse is expected to occur if the enzyme displays a negative co-operativity. The last product may either reverse a positive co-operativity into a negative one or, alternatively, strengthen an already negative co-operativity. The co-operativity generated by the mnemonical model has been compared to the kinetic behaviour of a random model. These two models have been shown to be discriminated on the basis of the departure they show with respect to the Michaelis-Menten behaviour. These theoretical considerations have been applied to previously published data, obtained with wheat germ hexokinase LI. This monomeric enzyme has a negative co-operativity with respect to the preferred substrate, glucose. The Hill coefficient decreases with MgATP concentration, increases with MgADP concentration and decreases with glucose-6-phosphate concentration. This is exactly what is to be expected on the basis of the above theory of kinetic co-operativity.
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PMID:Kinetic co-operativity of monomeric mnemonical enzymes. The significance of the kinetic Hill coefficient. 405 21

The results are reviewed from studies of activity of hexokinase (2.7.1.1.EC), dehydrogenase glucose-6-phosphate (1.1.1.49 EC), and cholinesterase (3.1.1.7 EC) in subcellular fractions of rat brain at the background of chemical sympathectomy induced by long-term administration of guanethidine and subsequent irradiation with a dose of 7 Gy. In conditions of sympathectomy, the enzyme activity is inhibited; in irradiated sympathectomized rats, activity of hexokinase and cholinesterase increases to reach the level of that of intact animals while dehydrogenase remains inhibited.
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PMID:[Brain enzyme activity in irradiated sympathectomized rats]. 408 Sep 98

The metabolism of mannose by human erythrocytes has been investigated. Phosphorylation of mannose is achieved by an enzyme with electrophoretic mobility on starch gel indistinguishable from the glucose-phosphorylating enzyme. Mannose phosphorylation is competitively inhibited by glucose; glucose phosphorylation is competitively inhibited by mannose. The K(i) values of inhibition are similar to the K(m) values for uninhibited phosphorylation. The normal average mannose-phosphorylating activity was found to be 0.69 U/g of Hb; the normal average glucose-phosphorylating activity was found to be 0.64 U/g of Hb. The ratio of mannose-phosphorylating activity to glucose-phosphorylating activity of a hemolysate prepared from the red cells of a subject with hexokinase deficiency was found to be within the normal range.Phosphomannose isomerase (PMI) activity of the red cells was found to average 0.064 U/g of Hb at its pH optimum of 5.9 with a mannose-6-phosphate (Man-6-P) concentration of 5 mmoles/liter. The enzyme activity in young cells was greater than activity in old cells. When human erythrocytes are incubated with mannose rapid accumulation of Man-6-P occurs, a finding indicating that PMI and not hexokinase is the limiting enzyme in the over-all conversion of mannose to fructose by the red cell. The ratio of mannose utilization to glucose utilization in hexokinase-deficient cells was greater than normal, as has been reported previously. These cells were found to have greatly increased PMI activity, presumably because of their young mean cell age. Consequently, Man-6-P accumulated only approximately one-third as rapidly as normal in hexokinase-deficient cells incubated with mannose. It is believed that the more rapid utilization of mannose relative to glucose by intact hexokinase-deficient cells may be explained on the basis of the regulatory effect of the PMI reaction on the rate of mannose utilization.
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PMID:Mannose metabolism in the human erythrocyte. 577 84

The relative rates of catabolism of glucose and glucose-6-phosphate by intact-cell suspensions of the meningopneumonitis agent, a member of the psittacosis group (Chlamydia), and the properties of the hexokinase and glucose-6-phosphate dehydrogenase of these suspensions were investigated. It is proposed that the hexokinase is a host enzyme bound to the surface of the meningopneumonitis cell and that glucose-6-phosphate is the first substrate in the conversion of hexose to pentose to be attacked by enzymes synthesized by the meningopneumonitis agent.
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PMID:Initial step in catabolism of glucose by the meningopneumonitis agent. 606 83

Aluminum inhibited both the cytosolic and mitochondrial hexokinase activities in rat brain. The IC50 values were between 4 and 9 microM. Aluminum was effective at mildly acidic (pH 6.8) or slightly alkaline (pH 7.2-7.5) pH, in the presence of a physiological level of magnesium (0.5 mM). However, saturating (8 mM) magnesium antagonized the effect of aluminum on both forms of hexokinase activity. Other enzymes examined were considerably less sensitive to inhibition by aluminum. The IC50 of aluminum for phosphofructokinase was 1.8 mM and for lactate dehydrogenase 0.4 mM. At 10-600 microM, aluminum actually stimulated pyruvate kinase. Aluminum also inhibited lactate production by rat brain extracts: this effect was much more marked with glucose as substrate than with glucose-6-phosphate. However, the IC50 for inhibiting lactate production using glucose as substrate was 280 microM, higher than that required to inhibit hexokinase. This concentration of aluminum is comparable to those reportedly found in the brains of patients who had died with dialysis dementia and in the brains of some of the patients who had died with Alzheimer disease. Inhibition of carbohydrate utilization may be one of the mechanisms by which aluminum can act as a neurotoxin.
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PMID:Inhibition of brain glycolysis by aluminum. 622 6

The effects of Cu2+ on glycolysis and several glycolytic enzymes were studied in rat brain extracts in vitro. At concentrations reportedly found in Wilson's disease, Cu2+ significantly inhibited lactate production from glucose or glucose-6-phosphate in rat brain postnuclear supernatant with an IC50 of about 3 microM. Cu2+ also inhibited several glycolytic enzymes. Amongst the latter, Cu2+ was most effective in inhibiting hexokinase (IC50 for Cu2+ = 7 microM), moderately effective in inhibiting pyruvate kinase (IC50 for Cu2+ = 56 microM), but least effective in inhibiting lactate dehydrogenase (IC50 for Cu2+ = 300 microM). These results suggest that inhibition of brain glycolysis may have pathophysiological importance in copper poisoning and in Wilson's disease.
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PMID:Neurotoxic effects of copper: inhibition of glycolysis and glycolytic enzymes. 624 58

A simple screening procedure for the detection of adenilate kinase (AK), hexokinase (Hx) or glucose-6-phosphate dehydrogenase (G6PD) deficiencies in blood, is described. It consists of two assays : in the first, the ATP formed by blood AK is coupled to Hx and G6PD, and in the second, the glucose-6-phosphate formed by blood Hx is coupled to G6PD. The enzyme activities are visually estimated by the reduction of NADP+ (non-fluorescent) to NADH (fluorescent). The appearance of fluorescence in the first assay indicates that the three enzyme activities are present. The absence of fluorescence could be due to the deficiency of any one of the three enzymes; in this case the second assay used in combination with the Beutler's screening test for G6PD permits the detection of the specific enzymatic deficiency.
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PMID:A simple screening procedure for adenylate kinase, hexokinase and glucose-6-phosphate dehydrogenase deficiencies. 625 22

Experiments conducted with a rat testicular tissue indicated that delta 9-tetrahydrocannabinol (THC) produced a dose-dependent inhibition of glucose metabolism. Incubation of testicular tissue with different U-14C-fructose concentrations and 0.3 mM THC also significantly inhibited 14CO2 production; however, testicular utilization of 214C-pyruvate remained unaffected by THC. In other experiments, 0.3 mM THC significantly decreased tissue concentrations of dihydroxyacetone phosphate, fructose-1,6-diphosphate, and glucose-6-phosphate by 23, 31 and 29%, respectively. Uptake studies with 14C-2-deoxy-D-glucose showed a 43% reduction in uptake of this substrate by testicular tissue in the presence of 0.3 mM THC. These studies demonstrate that THC has an inhibitory effect on the utilization of energy substrates by the testis. Sites of THC action may be the membrane uptake step, the hexokinase step, and/or possible the phosphofructokinase step. It is proposed that this inhibition of testicular glycolysis could deprive the cells of their energy reserves and thereby may disrupt many gonadal functions.
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PMID:Inhibitory effects of delta 9-tetrahydrocannabinol on glycolytic substrates in the rat testis. 627 42

Vanadate has been found to be a potent inhibitor of both the hydrolytic and synthetic activities of the multifunctional enzyme glucose-6-phosphatase (D-glucose-6-phosphate phosphohydrolase, EC 3.1.3.9). The enzyme, when studied in both microsomal preparations and in situ using permeable isolated hepatocytes, is inhibited by micromolar concentrations of vanadate. The inhibition by vanadate is greater in detergent-treated than in untreated microsomes. In both the microsomal preparations and permeable hepatocytes, the inhibition by vanadate is competitive with the phosphate substrate and is greater for the phosphotransferase than the hydrolase activity of the enzyme. The Ki values of vanadate for carbamyl-phosphate : glucose phosphotransferase and glucose-6-phosphate phosphohydrolase determined with permeable hepatocytes are in good agreement with the values determined with detergent-dispersed microsomes. The previously described inhibition of glucose-6-phosphate phosphohydrolase by ATP (Nordlie, R.C., Hanson, T.L., Johns, P.T. and Lygre, D.G. (1968) Proc. Natl. Acad. Sci. USA 60, 590-597) can now be explained by the vanadium contamination of the commercially available ATP samples used. In contrast with glucose-6-phosphatase, hepatic glucokinase and hexokinase were not inhibited by vanadate. Physiological implications and utilitarian experimental applicability of vanadate as a selective metabolic probe, based on these observations, are suggested.
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PMID:Vanadate: a potent inhibitor of multifunctional glucose-6-phosphatase. 627 21

In order to evaluate properly red cell metabolic data obtained in newborns with congenital hemolytic disorders, the unique metabolic characteristics and normal developmental changes that occur prenatally and postnatally are presented. The age-dependent red cell glycolytic enzymes (hexokinase, aldolase, pyruvate kinase) and glucose-6-phosphate dehydrogenase and most glycolytic intermediates are elevated at birth and at 11 to 12 months of age, consistent with the presence of a young red cell population the entire first year of life. However, certain red cell enzymes are elevated out of proportion to the age of the red cell population [phosphoglucose isomerase. glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase (PGK), and enolase (ENO)] whereas others are decreased [phosphofructokinase (PFK), glutathione peroxidase, carbonic anhydrase, and others]. These metabolic characteristics are felt to be unique and representative of "fetal erythropoiesis." Activities of PGK and ENO decrease the PFK increases toward normal adult values beginning at eight to nine weeks of age. The concentration of glucose-6-phosphate steadily increases after birth and peaks at three to four weeks of age, at a time when PFK activity remains relatively unchanged, suggesting a relative block in glycolysis at the PFK step secondary to an enzyme with both decreased activity and altered kinetic properties (a "fetal" isozyme). Thus, evaluation of red cell enzyme and glycolytic intermediate data obtained in the first year of life should be related to the knowledge that a young red cell population is present and the characteristic unique metabolic red cell alterations described in cord blood persist beyond the immediate neonatal period.
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PMID:Red cell enzymopathies in the newborn. I. Evaluation of red cell metabolism. 628 May 78


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