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 requirements of a cloned macrophage-like cell line, J774.16, for oxygen metabolism, and the nature of the defect in oxidative metabolism in a variant clone derived from it, J774.C3C, were studied. Upon stimulation with phorbol myristate acetate (PMA), the parental clone produced approximately 1 nmol O2-/min/10(6) cells, whereas the variant clone produced no detectable O2- under the same conditions. Sustained O2- production by J774.16 was totally dependent on extracellular glucose; in glucose-free medium, the cells initiated O2- production but could not sustain it. When cells were stimulated with PMA, glucose-C-1 oxidation of J774.16 cells increased 20-fold while that of J774.C3C remained at resting levels. O2- production in J774.16 cells was inhibited by some agents known to block mitochondrial electron transport before coenzyme Q, such as rotenone and tetrathiafulvalene, whereas antimycin A enhanced O2- production. A dissociation between O2- production and glucose-C-1 oxidation was observed when J774.16 was treated with certain metabolic inhibitors. Quinacrine, 2,4-dinitrophenol, chlorpromazine, and trifluoperazine inhibited O2- production completely under conditions in which glucose-C-1 oxidation was reduced only by 30%. Rotenone inhibited O2- production with no effect on glucose-C-1 oxidation whereas antimycin A augmented O2- production 50% but inhibited glucose oxidation by 20%. Glucose transport studies, with 2-deoxy-D-glucose, showed that the Km for glucose transport of both clones was about 1 mM, indicating that cells could effectively transport glucose even at low concentrations. The Vmax for glucose transport in both J774.16 and variant J774.C3C cells doubled after PMA stimulation, indicating that the variant was effectively stimulated by PMA, even though O2- was not produced. Similarly, PMA induced protein phosphorylation in both clones. No differences between clones J774.16 and J774.C3C in hexokinase, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, glutathione reductase, or glutathione peroxidase activities could be found. When dithionite-reduced and -oxidized difference spectra of plasma membranes of these clones were compared, comparable levels of b-type cytochrome were found in both clones. However, CO difference spectra indicated that CO was bound to a b-type cytochrome (presumed to be b-245) in clone J774.16 but not in J774.C3C.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Oxygen metabolism in cloned macrophage cell lines: glucose dependence of superoxide production, metabolic and spectral analysis. 631 50

The number and nature of glucose-phosphorylating enzymes of rat intestinal mucosa were investigated by chromatographic, electrophoretic, and kinetic methods. Three fractions with glucose-phosphorylating activity were obtained from the supernatant fluid of mucosa homogenate by means of DEAE-cellulose chromatography, corresponding to hexokinases A and B (EC 2.7.1.1.), and N-acetyl-D-glucosamine kinase (EC 2.7.1.59). Although the latter uses N-acetylglucosamine as the main substrate, it is also able to phosphorylate glucose. Electrophoresis in polyacrylamide and in cellulose acetate gels showed the same three enzyme activities. None of these procedures revealed the presence of either hexokinase D ("glucokinase") or hexokinase C in the intestinal mucosa. In the sediment fractions hexokinase A and B, but not N-acetylglucosamine kinase, were found. The Km values for glucose of partially purified hexokinases A and B were 0.025 and 0.174 mM, respectively, and their substrate specificity was the same as that of hexokinases A or B from other tissues. Partially purified N-acetylglucosamine kinase showed hyperbolic saturation functions for N-acetylglucosamine and ATP, with Km values of 0.021 and 0.38 mM, respectively. This enzyme also phosphorylated glucose, mannose, fructose, 2-deoxyglucose, and glucosamine. The dependence of velocity on glucose concentrations was complex, mimicking negative cooperativity. The molecular weight of both hexokinases A and B was 98,000 and that of N-acetylglucosamine kinase was 59,000. The kinetic properties, as well as the chromatographic and electrophoretic mobilities, of N-acetylglucosamine kinase may serve to confuse it with hexokinase D, and thus several criteria should be applied for correct identification.
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PMID:Kinetic, chromatographic and electrophoretic studies on glucose-phosphorylating enzymes of rat intestinal mucosa. 632 88

In vitro biochemical characteristics of three strains of Haemonchus contortus, benzimidazole-susceptible, mebendazole-resistant and thiabendazole-resistant isolates, were investigated. Steady-state pool sizes of glucose and metabolic intermediates, including adenine nucleotides and end-products revealed no differences between adult worms resistant or susceptible to benzimidazoles in 30-60 min incubations. Possible regulatory steps in the glycolytic pathway are identified as those involving the enzymes hexokinase, phosphofructokinase and pyruvate kinase. The major component of carbohydrate reserves was trehalose, some glycogen was present and the glucose pool was small. On incubation for 18 h in vitro, carbohydrates were metabolised in all three strains. However, in the benzimidazole-susceptible worms there was a preferential use of the glycogen reserves to maintain energy metabolism. All three strains had similar levels of total lipid, total protein and free amino acid and these did not change on incubation. The major products found in the medium on incubation, in vitro, for 18 h were propionate, acetate and propanol, with smaller amounts of ethanol, lactate and malate. All three strains produced a similar sum total of end-products; however, in the mebendazole-resistant strain there appeared to be a diversion of carbon flow to the ethanol-producing pathway. Carbon dioxide production in 60 min incubations was measured using radioactively labelled glucose. A greater output of labelled CO2 was noted under aerobic than anaerobic conditions. This was particularly true of the mebendazole-resistant strain and, in this strain, was sensitive to cyanide. The extent to which metabolic differences noted in the three strains may be related to benzimidazole resistance is not readily apparent.
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PMID:Energy metabolism of adult Haemonchus contortus in vitro: a comparison of benzimidazole-susceptible and -resistant strains. 642 5

Although aqueous outflow is most likely a passive, nonenergy-dependent process, alterations in cellular function in the trabecular meshwork presumably are involved in the development of some types of glaucoma. Accordingly, it seems important to define both the normal and abnormal biochemistry of this tissue. The authors have chosen glycolysis as their starting point, concentrating on the regulatory enzymes, hexokinase, and, in a companion paper, phosphofructokinase. Hexokinase activity has been measured in the 100,000 X g supernatant of homogenates prepared from excised calf trabecular meshwork. Treatment of the homogenate with Triton X-100 before centrifuging caused a twofold increase in measurable activity. Electrophoresis on cellulose acetate revealed types I and II isoenzymes. Electrophoresis on starch gel further resolved type 1 into the adult and fetal subtypes. The principal isoenzyme type released into solution by Triton X-100 was type 1. The kinetic behavior of hexokinase was measured by varying the concentrations of glucose at saturating levels of ATP. Kms calculated from these plots were 7.15 X 10(-2) M, 1.78 X 10(-3) M, and 1.19 X 10(-4) M. Apart from the fetal form of type I hexokinase, the isoenzymes from trabecular meshwork resemble those of other ocular tissues and most extraocular tissues. The special role, if any, of the fetal isoenzyme in regulating glycolysis is not known. Possibly, it is a "kinetically adaptable" isoenzyme.
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PMID:Hexokinase of calf trabecular meshwork. 649 Mar 30

Subcutaneous adipose tissue samples were obtained by biopsy technique and at slaughter from steers fed either a corn concentrate or pelleted alfalfa (roughage) diet. Steers fed the roughage diet had slightly greater metabolizable energy intakes than the concentrate-fed steers due to greater rates of feed intake; however, steers fed the concentrate diet had faster rates of gain, primarily in the fat depots. Diet had no effect on the incorporation of 14C-labeled acetate and lactate into fatty acids, although 3H2O incorporation into fatty acids was greater in the concentrate-fed steers. Although backfat thickness was 60% greater in the concentrate-fed steers, the number of adipocytes per gram adipose tissue was unaffected by diet, suggesting adipose cell hyperplasia. The activities of acetyl-CoA carboxylase, fatty acid synthetase, ATP citrate lyase, NADP+ malate dehydrogenase, and hexokinase were greater in the steers fed the concentrate diet; pyruvate kinase activity was unaffected by diet. Fatty acid synthesis and several lipogenic enzyme activities increased with age and then declined markedly by the time of the terminal biopsy. Basal and net rates of lipolysis generally were unaffected by diet but increased with age of the animal. As the animals gained weight, the ratio of net fatty acids released to glycerol released decreased, suggesting more extensive reesterification of fatty acids released during lipolysis.
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PMID:Interrelationships among diet, age, fat deposition and lipid metabolism in growing steers. 669 76

Two new battery-operated digital reflectance meters for blood glucose measurement have been tested for precision and accuracy in a laboratory trial. Reflocheck (Boehringer Company Ltd) is calibrated from a bar code printed on each test strip, Reflolux (Boehringer Company Ltd) from a bar code on acetate film provided with each bottle of BM-Test-Glycemie 20-800R strips, which can also be read visually. Three aqueous standards (3.3, 8.3 and 11.7 mmol/l) were assayed 10 times on each of 10 days. Overall coefficients of variation for Reflocheck were 2.8, 1.7 and 2.0% and for Reflolux 3.1, 1.5 and 2.8% respectively. One hundred and four blood samples measured on the machines gave very high correlations with a manual hexokinase assay: for Reflocheck, y = 1.1x - 0.7, r = 0.99 and for Reflolux, y = 1.07x + 0.1, r = 0.99. In the range 2.2-10 mmol, errors of 1 mmol or more occurred on seven occasions with Reflocheck and eight with Reflolux (n = 80) but none of these errors was of therapeutic significance. The performance of both machines was as good or better than previously published data for similar instruments. The ease of calibration and accuracy of both machines are advantageous as is the use of BM-Test-Glycemie 20-800R by Reflolux which enables a check to be made on visual readings.
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PMID:A laboratory trial of two new blood-glucose reflectance meters featuring automatic external calibration. 671 41

Rat brain mitochondrial hexokinase (ATP: D-hexose 6-phosphotransferase, EC 2.7.1.1) was solubilized by treatment of the mitochondria with glucose 6-phosphate and partly purified. The solubilized enzyme was compared with the cytosolic enzyme fraction. The solubilized and cytosolic enzymes were also compared with the enzyme bound to the mitochondrial membrane. The following observations were made. 1. There is no difference in electrophoretic mobility on cellulose-acetate between the cytosolic and the solubilized enzyme. Both fractions are hexokinase isoenzyme I. 2. There is no difference in kinetic parameters between the cytosolic or solubilized enzymes (P less than 0.001). For the cytosolic enzyme Km for glucose was 0.067 mM (S.E. = 0.024, n = 7); Km for MgATP2- was 0.42 mM (S.E. = 0.13, n = 7) and Ki,app for glucose 1,6-diphosphate was 0.084 mM (S.E. = 0.011, n = 5). For the solubilized enzyme Km for glucose was 0.071 mM (S.E. = 0.021, n = 6); Km for MgATP2- was 0.38 mM (S.E. = 0.11, n = 6) and Ki,app for glucose 1,6-diphosphate was 0.074 mM (S.E. = 0.010, n = 5). However when bound to the mitochondrial membrane, the enzyme has higher affinities for its substrates and a lower affinity for the inhibitor glucose 1,6-diphosphate. For the mitochondrial fraction Km for glucose was 0.045 mM (S.E. = 0.013, n = 7); Km for MgATP2- was 0.13 mM (S.E. = 0.02, n = 7) and Ki,app for glucose 1,6-diphosphate was 0.33 mM (S.E. = 0.03, n = 5). 3. The cytosolic and solubilized enzyme could be (re)-bound to depleted mitochondria to the same extent and with the same affinity. Limited proteolysis fully destroyed the enzyme's ability to bind to depleted mitochondria. 4. Our data support the hypothesis that soluble- and solubilizable enzyme from rat brain are one and the same enzyme, and that there is a simple equilibrium between the enzyme in these two pools.
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PMID:Mitochondrial and cytosolic hexokinase from rat brain: one and the same enzyme? 682 26

The kinetic properties of rabbit red blood cell hexokinase in different buffer systems have been studied. At pH 8.0 the reaction velocity (v) is about 30% higher in glycylglycine compared to Tris, Tea, Hepes or ammonium acetate buffers. The enzyme stability, heat-dependence and spectral properties of the enzyme are also affected by the buffer utilized. None of the following kinetic properties of red blood cell hexokinase varies with pH in the range 6.8-8.5: Km of glucose; Km of ATP and Ki of glucose 6-phosphate.
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PMID:Effects of buffers and pH on rabbit red blood cell hexokinase. 688 40

Isolated ovine adipocytes were incubated in vitro with specifically labeled 14C-glucose in the presence or absence of acetate. The flux patterns of glucose carbon through major metabolic pathways were estimated. When glucose was added as the sole substrate, approximately equal portions of glucose carbon (10%) were oxidized to CO2 in the pentose phosphate pathway, in the pyruvate dehydrogenase reaction and in the citrate cycle. Fifteen percent of the glucose carbon was incorporated into fatty acids and 43% was released as lactate and pyruvate. Addition of acetate to the medium increased glucose carbon uptake by 1.5-fold. Most of this increase was accounted for by a sevenfold increase in the activity of the pentose phosphate pathway. Acetate increased glucose carbon fluxes via pentose phosphate pathway to triose phosphates, from triose phosphate to pyruvate, into glyceride glycerol, into lactate and pyruvate and into pyruvate dehydrogenase and citrate cycle CO2. Glucose carbon incorporated into fatty acids was decreased 50% by acetate while, carbon fluxes through the phosphofructokinase-aldolase reactions were not significantly increased. Results of this study suggest that, when glucose is the sole substrate, the conversion of glucose to fatty acids in ovine adipocytes may not be limited by the maximum capacity of hexokinase, the pentose phosphate pathway or enzymes involved in the conversion of triose phosphates to pyruvate and of pyruvate to fatty acid. Acetate increased glucose utilization apparently by increasing activity of the pentose phosphate pathway as a result of enhanced NADPH utilization for fatty acid synthesis.
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PMID:Glucose metabolism and effect of acetate in ovine adipocytes. 714 48

Rat hexokinases fro caput sperm (immature) and caudal sperm (mature) were investigated. The hexokinases from both sources were studied by DEAE-cellulose column chromatography and by cellulose acetate electrophoresis. The specific activity of caput sperm hexokinase was not significantly different from that of the caudal sperm enzyme. Spermatozoa possess two isozymes of hexokinase. Type I hexokinase was the predominant type in caput sperm whereas the sperm type of hexokinase was predominant in caudal sperm. Hexokinase types II and III were absent in both extracts.
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PMID:Increase in sperm type hexokinase activity of rat spermatozoa during maturation. 720 84


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