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)

Epinephrine, hydrocortisone, and dibutyril cAMP inhibited glycolysis and glucogenolysis. The inhibitory effect was also found when glucose-6-phosphate (G-6-P) was used as a glycolysis substrate, but not for fructose-1,6-diphosphate. This is the evidence of hexokinase activity inhibition by hormones and dibutyril cAMP, and presumably of phospholylase and phosphofructokinase as well. In the simulated cell-free system the hormones produced no effect, dibutyril cAMP inhibiting hexokinase alone. For the realization of hormones effect their interaction with the cell membrane is required. Inhibition of glycogen and G-6-P decomposition to lactic acid in the rat liver slices was not associated with the hormone action on phosphorylase and phosphofructokinase through cAMP and proteinkinase directly. The results obtained indicated the existence of a supplementary mechanism that modified cAMP effect on the activity of the said enzymes. Insulin was effective in any of the cases.
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PMID:[Effect of adrenaline, hydrocortisone, insulin and dibutyryl-cAMP on glycolysis and glycogenolysis in white rat liver slices]. 21 83

1. Glucokinase was absent from chicken liver and only the low Km hexokinases, inhibited by AMP, ADP but not ATP, were present. 2. The Km of chicken liver glucose-6-phosphatase for glucose-6-phosphate was reduced from 5.65 to 3.75 mM following starvation, and the enzyme was inhibited by glucose. 3. Starvation of chickens for 24 hr slightly lowered the hexokinase activity and doubled glucose-6-phosphatase activity; it did not change subcellular distribution of the enzymes. Oral glucose rapidly restored the activities to fed values. 4. It was concluded that glucose uptake into, and efflux from, chicken hepatocytes, was regulated by the activity and kinetic characteristics of glucose-6-phosphatase and by the glucose-6-phosphate concentration, and that the hexokinases had little regulatory function.
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PMID:Glucose phosphorylation and dephosphorylation in chicken liver. 23 87

The denaturation of eight purified yeast enzymes, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, 3-phosphoglycerate kinase, alcohol dehydrogenase, beta-fructosidase, hexokinase and glucose-6-phosphate isomerase, promoted under controlled conditions by the free fatty acids myristic and oleic, is selective. Glucose-6-phosphate dehydrogenase (D-glucose-6-phosphate:NADP+ 1 oxidoreductase, EC 1.1.1.49) is extremely sensitive to destabilization and was studied in greater detail. Results show that chain length and degree of unsaturation of fatty acids are important to their destabilizing effect, and that ligands of the enzyme can afford protection. The denaturation process results in more than one altered form. These results can be viewed in the perspective of the possibility that amphipathic substances, and in particular free fatty acids, may play a role for enzyme degradation in vivo, by initiating steps of selective denaturation.
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PMID:Selective denaturation of several yeast enzymes by free fatty acids. 35 87

The levels of glucose-6-phosphate and 6-phosphogluconate dehydrogenase in wildtype cells of Aspergillus nidulans varied with the carbon and nitrogen source. In general, hexokinase activity did not vary with carbon or nitrogen source. The ammonium derepressed mutant amrA1 had only 50% of the wildtype level of hexokinase. Phosphoglucomutase activity was low in wildtype cells grown with nitrate, but high in cells grown with ammonium when glucose was the carbon source. A non-inducible mutant, nirA-1, in the regulatory gene for nitrate reductase, had high phosphoglucomutase activity when grown with nitrate or ammonium. A constitutive mutant nirAc1, in the regulatory gene for nitrate reductase had low phosphoglucomutase activity when grown with nitrate or ammonium. The mutants nir-1 and nirAc1 are recessive and semi-dominant respectively for abnormal phosphoglucomutase activity.
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PMID:The regulation of hexokinase and phosphoglucomutase activity in Aspergillus nidulans. 37 22

Type I hexokinase (ATP:D-hexose 6-phospotransferase, EC 2.7.1.1) of porcine heart exists in two chromatographically distinct forms. These do not differ significantly in size, electrophoretic mobility at pH 8.6 or kinetic properties. Both forms obey a sequential mechanism and are potently inhibited by glucose 6-phosphate. In contrast to observations of type I hexokinase from brain, inhibition by glucose 6-phosphate is not relieved by inorganic phosphate. Under most conditions, low concentrations of phosphate (less than 10 mM) have little effect on the kinetic behaviour of the enzyme but at higher concentrations this ligand is an inhibitor. Mannose 6-phosphate inhibits in a manner analogous to glucose 6-phosphate but the Ki is much greater. In view of the similarity of the kinetic parameters governing phosphorylation of mannose and glucose, this difference in affinity for the inhibitor site is seen as consistent with the existence of a separate regulatory site on the enzyme. MgADP inhibits hexokinase but behaves as a normal product inhibitor and inhibition is competitive with respect to MgATP and non-competitive with respect to glucose.
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PMID:Comparison of type I hexokinases from pig heart and kinetic evaluation of the effects of inhibitors. 42 Aug 59

In rats, starting from a month or three-months age, stayed for 2 months on a diet with 54 per cent of saccharose in the saliva the activity of hexokinase, aldolase, malate-dehydrogenase, sorbitol-dehydrogenase, glutamate-dehydrogenase, glucose-6-phosphate-dehydrogenase and the content of lactate, pyruvate and glucose were determined. In the activity of significant differences of enzymes and carbohydrate metabolites in the saliva of three- and five-months old rats were not disclosed. Keeping of the one-month rats for 2 months on the saccharose diet increased the activity of enzymes (except for malate-dehydrogenase) and raised the amount of lactate and pyruvate. In five-month rats receiving the saccharose ration starting from three-month age a tendency towars a rising activity of hexoninase and to a falling malate-dehidrogenase activity were noted. The activity of other enzymes and the lactate level remained unchageed. In young rats given a saccharose diet the presence of an enzymatic shift toward intensification of the anaerobic glycolysis was confirmed by change in the isofermentative spectrum of the lactate-dehydrogenase accompanied by a drop of the total amount of aerobic isoenzymes LDG1, LDG2 and also by an excess accumulation of pyruvate and lactate.
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PMID:[Effect of a saccharose diet on the enzymatic activity and the metabolite content from carbohydrate metabolism in the saliva of rats of varying age]. 43 32

A theory is presented that associates burst (orlag) kinetics with the respective concentrations of enzyme initial states X1 and X6 and with the cooperation of a mnemonical enzyme. The theory predicts that for an enzyme with a negative cooperation, decreasing the initial concentration of X1 (or increasing that of X6) tends to increase the induction time. This increase may correspond to a reversal of a burst in a lag. Similarly, if the enzyme has a positive cooperation, decreasing the initial concentration of X6 (or increasing that of X1) increases the induction time. The first case above is expected to apply to wheat germ hexokinase LI, X1 being the form that binds glucose preferentially, and X6 the one that binds glucose 6-phosphate. By changing solely the respective concentrations of the two initial forms, one may expect to modify the pre-steady-state phase but not the steady-state kinetics of the reaction. By jumping the temperature of the enzyme solution from 4 degrees C to 30 degrees C and letting the transconformation ewuilibrium relax for various periods of time before mixing enzyme with the substrates, one can analyse the effect of the relative concentrations of X1 and X6 on the induction time. One can estimate in that way one of the rate constants of the transconformation between the two free enzyme forms. The shorter the incubation time at 30 degrees C then the smaller is the negative induction time (in absolute values). Another possibility of controlling the ratio between the two initial concentrations of the enzyme, is to pre-mix hexokinase with glucose 6-phosphate and to arrange that glucose-6-phosphate concentration, after mixing enzyme and substrates, is held constant whatever the pre-mixing conditions. When wheat germ hexokinase LI is pre-mixed 30 min at 30 degrees C with glucose 6-phosphate before the reaction starts, the burst does not disappear. If, on the other hand, pre-mixing is effected at 4 degrees C the burst is reversed into lag. This result is taken to mean that the equilibrium constant between the two free enzyme forms (the 'circle' and the 'rhombus') is strongly dependent on temperature. A direct study of the effect of glucose 6-phosphate on the conformational equilibrium of wheat germ hexokinase, gives support to this interpretation. If hexokinase is mixed at 4 degrees C with glucose 6-phosphate a slow increase in fluorescence of tryptophanyl residues is observed, which indicates that the 'rhombus' conformation accumulates under these conditions. On the other hand, at 30 degrees C, glucose 6-phosphate does not produce any significant change in the fluorescence of the protein. As expected, these results imply that the equilibrium between the two free enzymes species is freely reversible a 4 degrees C and nearly irreversible at 30 degrees C. The equations derived from the mnemonical model allow fitting or simulation of the experimental results.
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PMID:Enzyme memory. Effect of glucose 6-phosphate and temperature on the molecular transition of wheat-germ hexokinase LI. 46 32

Recent evidence has suggested a role for the polyol pathway in pathogenesis of cell damage in diabetes Glucose may be phosphorylated to glucose-6-phosphate via hexokinase and enter glycolysis or reduced to sorbitol via aldose reductase to enter the polyol pathway. The poorly diffusible sorbitol is converted via sorbitol dehydrogenase to fructose. Hexokinase, aldose reductase and sorbitol dehydrogenase activities were measured in glomeruli (G) and small arteries (SA) taken from normal and diabetic human kidneys, Hexokinase in diabetic G was 1688, which was significantly decreased from normal, 3147 mmoles/kg-1/h-1. Alodse reductase was significantly elevated in diabetic G,56-6, compared to normal G,10-8 mmoles/kg-1/h-1. In contrast, sorbitol dehydrogenase was significantly depressed in diabetic G, 3-7 VERSUs 10-9 mmoles/kg-1/h-1. The enzymatic changes observed in diabetic G would facilitate accumulation of sorbitol and therefore could contribute to the progression of glomerulosclerosis. The activity of hexokinase was also significantly reduced in SA, whereas aldose reductase and sorbitol dehydrogenase were unchanged.
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PMID:Quantitative histochemistry of the sorbitol pathway in glomeruli and small arteries of human diabetic kidney. 48 51

Various enzymes of glycolysis (hexokinase, phosphoglucoisomerase, aldolase and lactate dehydrogenase), the Krebs cycle (isocitrate, succinic and malate dehydrogenases), and the pentose phosphate cycle (glucose-6-phosphate and 6-phosphogluconate dehydrogenases) were studied in buffalo spermatozoa by biochemical and cytochemical methods. The enzymes of glycolysis were found to be loosely bound whereas those of the Krebs and pentose phosphate cycles were strongly bound to mitochondrial membranes. All the enzymes studied were localized histochemically in the mid-piece.
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PMID:Glycolytic, Krebs cycle and pentose phosphate cycle enzymes in spermatozoa of the buffalo (Bubalus bubalis). 51 3

Mitochondria from rabbit reticulocytes contain about 50% of the total reticulocyte hexokinases. The proportion of mitochondrial hexokinases may be changed under different metabolic conditions. Mitochondrial bound and soluble hexokinases exhibit different kinetic properties (KMATP and glucose-6-phosphate inhibition). The respiratory rate of isolated reticulocyte mitochondria in the presence of glucose depends on the glucose-6-phosphate concentration, as the ADP generation by the endogenous hexokinases is strongly inhibited by glucose-6-phosphate. In the experimental system all intermediary states of mitochondrial respiration can be adjusted between the state of maximal activity (state 3 or active state) and the controlled or resting state (state 4) by different glucose-6-phosphate levels. The stationary levels of the extramitochondrial adenine nucleotides in this experimental system have been measured. The rate of mitochondrial respiration and ATP formation depends on the extramitochondrial ATP/ADP ratio. At ratios of about 10 and lower the mitochondria are in their maximum phosphorylation state, at higher ratios the mitochondrial ATP formation is controlled by the extramitochondrial ATP/ADP ratio. It is postulated that the close intercounnection between the mitochondrial hexokinase and the mitochondrial ATP forming system in reticulocytes is of funcitonal significance for mitochondrial-cytosolic interactions in rabbit reticulocytes and probably in other types of cells with mitochondrial hexokinases, too.
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PMID:Studies on the functional significance of mitochondrial bound hexokinase in rabbit reticulocytes. 59 66


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