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 ligands (glucose, ATP and Mg2+) and zwitterionic micelles of lysophosphatidylcholine (LPC) or N-hexadecyl-N,N-dimethyl-3-ammonium propanesulfonate (HPS) in the yeast hexokinase (HK) stability was studied at 35 degrees C. The thermal inactivation kinetics followed one-exponential decay. The effect of ligands on protecting the enzyme against inactivation followed the order: glucose > glucose/Mg2+ >ATP/Mg2+ approximately or approximately equal to Mg2+l approximately or approximately equal to buffer only. Both LPC and HPS micelles increased the enzyme stability only when the incubation medium contained glucose or glucose/Mg2+, suggesting that the protein conformation is a key prerequisite for the enzyme-micelle interaction to take place. This enzyme-micelle interaction resulted in an increased catalytic efficiency (with a decrease in Km for ATP and increase in Vmax as well as in changes on the tertiary (intrinsic fluorescence) structure of the yeast hexokinase.
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PMID:Increased stability and catalytic efficiency of yeast hexokinase upon interaction with zwitterionic micelles. Kinetics and conformational studies. 1088 10

Extracellular ATP regulates a variety of functions in epithelial tissues by activating the membrane P2-receptor. The purpose of this study was to investigate the autocrine/paracrine regulation by luminal ATP of electrogenic amiloride-sensitive Na(+) absorption in the distal colon from guinea pigs treated with aldosterone by measuring the amiloride-sensitive short-circuit current (I(sc)) and (22)Na(+) flux in vitro with the Ussing chamber technique. ATP added to the luminal side inhibited the amiloride-sensitive I(sc) and (22)Na(+) absorption to a similar degree. The concentration dependence of the inhibitory effect of ATP on amiloride-sensitive I(sc) had an IC(50) value of 20-30 microM, with the maximum inhibition being approximately 50%. The effects of different nucleotides and of a nucleoside were also studied, the order of potency being ATP = UTP > ADP > adenosine. The effects of ATP were slightly, but significantly, reduced in the presence of suramin in the luminal solution. The inhibitory effect of luminal ATP was more potent in the absence of both Mg2+ and Ca2+ from the luminal solution. Pretreatment of the tissue with ionomycin or thapsigargin in the absence of serosal Ca2+ did not affect the percent inhibition of amiloride-sensitive I(sc) induced by ATP. Mechanical perturbation with a hypotonic luminal solution caused a reduction in amiloride-sensitive I(sc), this effect being prevented by the presence of hexokinase, an ATP-scavenging enzyme. These results suggest that ATP released into the luminal side by hypotonic stimulation could exert an inhibitory effect on the electrogenic Na(+) absorption. This effect was probably mediated by a P2Y(2) receptor on the apical membrane of colonic epithelial cells, and a change in the intracellular Ca2+ concentration may not be necessary for this process.
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PMID:Role of luminal ATP in regulating electrogenic Na(+) absorption in guinea pig distal colon. 1212 76

It has been found that mitochondria isolated from the flight muscle of the housefly, Musca domestica, are capable of effecting oxidative phosphorylation. A systematic investigation of the factors which regulate this coupling was undertaken. It was found: 1. The molarity of the isolation medium had considerable influence on the morphology of the mitochondria. These physical alterations were associated with changes in oxidation, phosphorylation, and ATPase activity. 2. In addition to an optimum isolation medium, the normal morphology of the mitochondria needed to be further stabilized by serum albumin. 3. A "latent" ATPase activity in insect mitochondria was demonstrated. An inverse relationship was found between oxidative phosphorylation and ATPase activity. 4. Oxygen consumption and the uptake of phosphate were linear with respect to time. 5. A respiratory substrate was necessary for phosphorylation and for maintenance of spatially organized mitochondria. 6. No differences in oxygen uptake were found in the presence or absence of inorganic phosphate. 7. Magnesium was required for optimal oxidative phosphorylation. Calcium and manganese inhibited both respiration and phosphorylation. 8. The addition of cytochrome c had no effect on either oxygen or phosphate uptake. 9. ATP, ADP, or AMP were capable of participating in oxidative phosphorylation, but the glucose-hexokinase trapping system was necessary. 10. Fluoride inhibited the phosphorylation of AMP, but increased P/O when ATP was used. This stimulation was not due to the inhibition of ATPase. 11. Neither arginine nor creatine was phosphorylated. 12. The addition of other isolated fractions of flight muscle to the mitochondrial system had no appreciable effect on respiration or phosphorylation.
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PMID:Investigations on the mitochondria of the housefly, Musca domestica L. III. Requirements for oxidative phosphorylation. 1311 5

A recombinant thermophilic Thermus caldophilus GK24 hexokinase, one of the ROK-type (repressor protein, open reading frames, and sugar kinase) proteins, exists uniquely as a 120 kDa molecule with four subunits (31 kDa), in contrast to eukaryotic and bacterial sugar kinases which are monomers or dimers. The optimal temperature and pH for the enzyme reaction are 70-80 degrees C and 7.5, respectively. This enzyme shows broad specificity toward glucose, mannose, glucosamine, allose, 2-deoxyglucose, and fructose. To understand the sugar specificity at a structural level, the enzyme-ATP/Mg2+-sugar binding complex models have been constructed. It has been shown that the sugar specificity is probably dependent on the interaction energy occurred by the positional proximity of sugars bound in the active site of the enzyme, which exhibits a tolerance to modification at C2 or C3 of glucose.
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PMID:A hexokinase with broad sugar specificity from a thermophilic bacterium. 1605 15

In this work, the effects of visible (655 nm) and near-infrared (830 nm) light on ATP in solution were examined. The addition of irradiated ATP to the hexokinase reaction caused significant differences in the reaction rates and in the Michaelis-Menten kinetic parameters, k(m) and v(max). Irradiated ATP cleavage by hexokinase occurred in less time. Changes were wavelength and dose dependent. Excitation of ATP with a 260 nm wavelength ultraviolet light induced a fluorescence emission that was decreased when Mg2+ was added due to ion binding of the phosphates, which are the structures that modify the fluorescence produced by the adenine dipoles. The irradiation of this ATP.Mg2+ solution using 655 and 830 nm light increased the fluorescence by a possible displacement of Mg2+ from the phosphates. In conclusion, visible and near-infrared light modifies the biochemical behavior of ATP in the hexokinase reaction and the fluorescence intensity of the molecule thus altering the Mg2+ binding strength to the oxygen atoms in the phosphate group.
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PMID:Modification of the intrinsic fluorescence and the biochemical behavior of ATP after irradiation with visible and near-infrared laser light. 1610 16

1. A method is described for the isolation of hexokinase from baker's yeast. The method is based mainly on fractionation with alcohol and results See PDF for Structure in a 30-fold increase in specific activity. The final product could be crystallized from ammonium sulfate without change in specific activity. 2. The enzyme catalyzes a transfer of phosphate from adenosinetriphosphate to glucose, fructose, or mannose, the relative rates with these three sugars being 1:1.4:0.3. 3. With glucose as substrate, the turnover number for the crystalline enzyme is 13,000 moles of substrate per 10(5) gm. of protein per minute at 30 degrees and pH 7.5. The temperature coefficient (Q(10 degrees )) between 0 and 30 degrees is 1.9. 4. Magnesium ions are necessary for the activity, the dissociation constant for the Mg(++) -protein complex being 2.6 x 10(-3). Fluoride in concentrations as high as 0.125 M has no inhibitory effect on the enzyme when the Mg(++) and orthophosphate concentrations are 6.5 x 10(-3)M and 1 x 10(-3)M, respectively. 5. The crystalline enzyme shows a loss in activity when highly diluted. This loss in activity can be prevented by diluting in the presence of small amounts of other proteins. Of the various protective proteins tested, insulin was the most effective, providing complete protection in a concentration of 6 micrograms per cc.; with serum albumin, a concentration of 60 micrograms per cc. was necessary. Thiol compounds (cysteine, glutathione) exerted no protective action. 6. The inactivation of the crystalline enzyme on incubation with trypsin can be prevented to a marked degree by the presence of glucose. The instability of crude preparations of yeast hexokinase may be attributed to the presence of proteolytic enzymes, since glucose or fructose has a remarkable protective effect on such preparations.
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PMID:ISOLATION OF HEXOKINASE FROM BAKER'S YEAST. 1987 67


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