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 mechanism of retraction of the longitudinal flagellum of Ceratium tripos was studied by making extracted models of the flagellum. Non-detergent models extracted in low ionic strength medium containing 1 M-glucose, 10 mM-EDTA, and 50 mM-Tris X HCl buffer (pH 8.0), retracted when Ca2+, Mg2+, Ba2+, Sr2+, Mn2+ or Cd2+ was applied locally with a glass capillary. A demembranated model of the flagellum was made with an extraction medium containing 0.8-1.0 M-glucose, 20 mM-Tris-acetate (pH 7.8), 2 mM-EGTA, 5-7 mM-MgSO4, 0.1 M-potassium glutamate and 0.1% Triton X-100. The model required a concentration of Mg2+ of a few mmol/l for successful reactivation of both retraction and undulation, and about 0.1 M-potassium glutamate (or sodium glutamate) for reactivation of undulation. Neither type of motion of the models could be reactivated above 35 degrees C. Ca2+ induced the retraction at pCa 5.5 or less. In addition to Ca2+, Mn2+, Ba2+, Sr2+ and Cd2+ also induced retraction but Mg2+, La3+ or Tb3+ did not. Although ATP was required for undulation, it was not required for retraction. Co-incubation with hexokinase to remove contaminating ATP did not suppress the retraction. The potent ATPase inhibitor, orthovanadate, inhibited undulation at 10 micron but did not inhibit retraction even at 2 mM. SH blockers, N-ethylmaleimide and dithio-bis-nitrobenzoic acid strongly suppressed undulation but had no effect on retraction. Calmodulin inhibitors, trifluoperazine and chlorpromazine, also had no effect on retraction. These data indicate that undulation is generated by a 9 + 2 microtubular axoneme using energy released by hydrolysis of ATP and that retraction can be induced by Ca2+ without a requirement for ATP.
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PMID:Extraction model of the longitudinal flagellum of Ceratium tripos (Dinoflagellida): reactivation of flagellar retraction. 385 92

Inositol 1,4,5-trisphosphate (InsP3) releases Ca2+ from the non-mitochondrial Ca2+ store site of various types of cells. To study the mechanisms of the Ca2+ release from the store site, the effect of InsP3 on the passive Ca2+ release and influx, and the active Ca2+ uptake in the presence of oxalate, was examined using saponin-treated guinea pig peritoneal macrophages. InsP3 stimulated the passive Ca2+ release and influx. Although InsP3 slightly inhibited the active Ca2+ uptake in the presence of oxalate, it seems unlikely that the Ca2+ release by this agent is caused by the inhibition of the Ca2+ uptake, because the addition of apyrase or hexokinase (which removes ATP within 30 s, so that no more Ca2+ can be accumulated) or vanadate (which inhibits the Ca2+ uptake) resulted in very slow release of Ca2+. These results suggest that the Ca2+ permeability of the Ca2+ store membrane is increased by InsP3. InsP3 did not cause an increase in the Ca2+ permeability of phospholipid vesicles (liposomes), indicating that this agent may bring about Ca2+ release by a specific effect on the physiologically relevant Ca2+ channels or carriers in the non-mitochondrial Ca2+ store site. The passive Ca2+ release by InsP3 was enhanced by ATP and an unhydrolyzable ATP analogue, 5'-adenylyimidodiphosphate, but not by ADP or AMP. The passive Ca2+ release by InsP3 was observed even at 0 degree C.
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PMID:Increase in Ca2+ permeability of intracellular Ca2+ store membrane of saponin-treated guinea pig peritoneal macrophages by inositol 1,4,5-trisphosphate. 387 10

Permeabilized hepatocytes accumulated 45Ca2+ into a non-mitochondrial pool when provided with ATP. 45Ca2+ efflux from this pool was revealed by removal of ATP with glucose and hexokinase or by inhibiting uptake with NaVO3. The effect of inositol 1,4,5-trisphosphate (IP3) on 45Ca2+ efflux from the pool was investigated. IP3 (5 microM) evoked a rapid increase in the rate of 45Ca2+ efflux. Kinetic analysis of the effect of IP3 indicated the existence of two distinct Ca2+ fractions within the pool; only one, accounting for about one-third of the ATP-dependent Ca2+ content of the pool, was responsive to IP3. The effect of IP3 on 45Ca2+ efflux from the non-mitochondrial pool does not require ATP, a finding that is inconsistent with a previous suggestion that this effect may be mediated by protein phosphorylation.
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PMID:Size of the inositol 1,4,5-trisphosphate-sensitive calcium pool in guinea-pig hepatocytes. 387 72

The effect of hypoparathyroidism and low blood calcium on enzyme levels in rat liver and kidney is shown. Four animal groups were used: parathyroidectomized (PTX), PTX with CaCl2 added in the drinking water, sham-operated controls and sham-operated with CaCl2 added in the drinking water. PTX significantly lowered serum parathyroid hormone (PTH) and calcium. Supplementation of CaCl2 in the drinking water increased serum Ca levels in PTX rats but not in the controls. Significant changes in several liver and kidney enzymes were seen. Most affected were the liver NADP dependent enzymes, glucose-6-phosphate dehydrogenase and malic enzyme. Similar patterns but with relatively smaller changes were seen in the liver enzymes, lactic dehydrogenase, hexokinase, and aspartate transferase. No significant differences between the groups were seen in the levels of malic dehydrogenase, isocitric dehydrogenase, fructose-6-phosphate kinase and cholinesterase. In the kidney, which was less affected than the liver, the only significant difference was seen in the level of malic enzyme. Serum total lipids in the PTX group were significantly lower. All the changes seen were partially reversed by Ca supplementation in the drinking water.
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PMID:Biochemical change in the liver and kidney of rats following parathyroidectomy. 400 1

Addition of 0.4-25 microM extracellular ATP results in transient, dose-dependent increases in cytosolic free calcium measured in Ehrlich ascites tumor cells. In cells incubated with 1 mM extracellular Ca2+, ATP induces a triphasic Ca2+ transient: an initial rapid increase (2-3 s), a second, slower phase of increase (60-90 s), and, finally, a gradual return to near resting [Ca2+]i (4-5 min). Several findings demonstrate that the initial, rapid phase of Ca2+ transient results from a mobilization of Ca2+ from a non-mitochondrial intracellular store, while the second, slow phase of increase is produced by enhanced influx of Ca2+ across the plasma membrane. Successive additions of extracellular ATP can elicit repetitive Ca2+ transients if the initially added ATP is removed either through the action of native ecto-ATPase activity or exogenous hexokinase. Other adenine nucleotides, including non-hydrolyzable ATP analogs, neither alter cytosolic [Ca2+] nor antagonize the ATP-induced effects. Conversely, other nucleotide triphosphates (ITP, UTP, and GTP) induce Ca2+ transients which are identical to those produced by ATP. A variety of experimental results indicate that these actions of ATP and other nucleotide triphosphates are not due to a generalized increase in plasma membrane permeability. The results suggest that, in these transformed cells, ATP may act in a manner similar to other Ca2+ mobilizing hormones and growth factors.
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PMID:Intracellular Ca2+ mobilization activated by extracellular ATP in Ehrlich ascites tumor cells. 403 Jul 63

The present study shows that in brain mitochondria the active calcium uptake and the sodium-dependent calcium efflux are modulated by the porin-bound enzyme hexokinase. The release of the enzyme, promoted by glucose-6-phosphate (G-6-P), under conditions which do not affect mitochondrial functions, is accompanied by a decrease of the rates of fluxes of the cation. This phenomenon is discussed and correlated with the formation of microcompartments between the inner and outer mitochondrial membranes, where the hexokinase-porin complex may constitute a regulating gate system for calcium.
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PMID:The role of hexokinase as a possible modulator of Ca2+ movements in isolated rat brain mitochondria. 403 8

ATP-dependent Ca2+ sequestration by rat liver microsomes was assayed using three different methods, and characterized with regard to the effect of various inhibitors. When glucose and hexokinase were added in combination to deplete ATP in the incubation, Ca2+ uptake was followed by rapid release of Ca2+ from the microsomes. Ca2+ sequestration was inhibited by reagents that cause alkylation (e.g. p-chloromercuribenzoate) or oxidation (e.g. diamide) of protein sulfhydryl groups. Moreover, pretreatment of the microsomes with cystamine, which causes formation of mixed disulfides with protein thiols, also resulted in the inhibition of Ca2+ sequestration. It is concluded that microsomal Ca2+ sequestration is critically dependent on protein sulfhydryl groups, and that modification of protein thiols may be an important mechanism for the inhibition of microsomal Ca2+ sequestration by a variety of toxic agents.
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PMID:On the role of thiol groups in the inhibition of liver microsomal Ca2+ sequestration by toxic agents. 405 10

Exposure of red cells to fluoride produces a variety of metabolic alterations, most of which are based upon the secondary effects of enolase inhibition, which reduces pyruvate synthesis and interferes with the regeneration of diphosphopyridine nucleotide (NAD). Adenosine triphosphate (ATP) is consumed in the hexokinase and phosphofructokinase reactions but is not regenerated since the deficiency of NAD limits glyceraldehyde phosphate dehydrogenase. ATP depletion in the presence of fluoride and calcium induces a massive loss of cations and water. Of the other known sites of ATP utilization, membrane-bound ATPase is inhibited by fluoride, but the incorporation of fatty acids into membrane phospholipids is unaffected until ATP is depleted. The addition of methylene blue to fluoride-treated red cells regenerates NAD, permitting triose oxidation and the generation of 3-phosphoglycerate and 2,3-diphosphoglycerate. Enolase inhibition is then partially overcome by mass action, and sufficient glycolysis proceeds to maintain the concentration of ATP. This in turn prevents the massive cation and water loss, and permits membrane phospholipid renewal to proceed. Membrane ATPase activity is not restored by the oxidant so that normal cation leakage remains unopposed by cation pumping in red cells exposed to the combination of fluoride and methylene blue.
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PMID:Energy metabolism in human erythrocytes. I. Effects of sodium fluoride. 432 3

The regulation of extramicrosomal Ca2+ concentration maintained by suspensions of rat insulinoma microsomes was studied using Ca2+-selective minielectrodes. The Ca2+-transporting activity was MgATP dependent and correlated with the endoplasmic reticulum marker NADPH-cytochrome c reductase. When incubated in a high KCl medium containing Mg2+ and phosphate, the microsomes lowered [Ca2+] within less than 10 min to around 0.2 microM. They had a high Ca2+-sequestering activity since they were able to take up and retain several small Ca2+ additions. No evidence for a Na+/Ca2+ countertransport was obtained. The accumulated Ca2+ was released by the Ca2+ ionophore A23187 or upon transforming ATP into ADP using glucose plus hexokinase. The addition of ADP, at concentrations present in cells, resulted in a dose-dependent and reversible net Ca2+ efflux from the microsomes until a higher [Ca2+] steady state was reached. This was specific for ADP since GDP, UDP, CDP, IDP, and the nonhydrolyzable analogue methylene-ADP as well as AMP and cAMP did not reproduce the effect. Insulin secretory granules were unable to lower medium [Ca2+] or to take up a pulse addition of Ca2+. However, most of the large granular calcium content was released by A23187. The addition of Na+ and lowering or increasing medium pH by 0.2 pH unit did not induce Ca2+ uptake or efflux from the secretory granules. The results indicate that insulinoma endoplasmic reticulum but not insulin secretory granules may play a critical role in the regulation of cytosolic Ca2+. A variation in cellular ADP content following secretagogue addition might modulate Ca2+ fluxes across the endoplasmic reticulum and contribute in raising cytosolic Ca2+.
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PMID:Regulation of Ca2+ transport by isolated organelles of a rat insulinoma. Studies with endoplasmic reticulum and secretory granules. 608 82

Deciliation of Paramecium tetraurelia by a Ca2+ shock procedure releases a discrete set of proteins which represent about 1% of the total cell protein. Marker enzymes for cytoplasm (hexokinase), endoplasmic reticulum (glucose-6-phosphatase), peroxisomes (catalase), and lysosomes (acid phosphatase) were not released by this treatment. Among the proteins selectively released is a Ca2+-dependent ATPase. This enzyme has a broad substrate specificity which includes GTP, ATP, and UTP, and it can be activated by Ca2+, Sr2+, or Ba2+, but not by Mg2+ or by monovalent cations. The crude enzyme has a specific activity of 2-3 mumol/min per mg; the optimal pH for activity is 7.5. ATPase, GTPase, and UTPase all reside in the same protein, which is inhibited by ruthenium red, is irreversibly denatured at 50 degrees C, and which has a sedimentation coefficient of 8-10 S. This enzyme is compared with other surface-derived ATPases of ciliated protozoans, and its possible roles are discussed.
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PMID:A Ca2+-activated ATPase specifically released by Ca2+ shock from Paramecium tetraurelia. 612 13


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