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)

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

The role of mitochondrial hexokinase (EC 2.7.1.1.) and mitochondrial ATP synthesis in the utilization of glucose for the support of estrogen biosynthesis was examined in placental mitochondrial preparations supplemented with NADP+, glucose-6-phosphate dehydrogenase (EC 1.1.1.49) and 4-androstene-3,17-dione. With 14 mitochondrial preparations, rates of steroid aromatization supported by 100 mM glucose and 20 mM ATP had a mean of 65.7 +/- 7.1 (SD) % of rates achieved with saturating levels of glucose 6-phosphate. ADP, but not AMP, could substitute for ATP in this system. Aromatization supported by glucose and high concentrations of ADP was inhibited by AMP but not by 2,4-dinitrophenol or oligomycin. Glucose also supported mitochondrial aromatization when combined with a respiratory chain-linked metabolic substrate (glycerol 3-phosphate) and a limiting concentration of ADP (2 mM). This support was inhibited by 2,4-dinitrophenol, the p-trifluoromethoxyphenylhydrazone of carbonyl cyanide, oligomycin and atractyloside. Thus, glucose metabolism by mitochondrial hexokinase, utilizing ATP generated either by oxidative phosphorylation or mitochondrial adenylate kinase (EC 2.7.4.3), can be coupled with a soluble NADPH-generating system to provide effective support of mitochondrial estrogen synthesis.
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PMID:The support of steroid aromatization by mitochondrial metabolic activities of the human placenta. 670 59

1. The following were measured in pieces of perirenal adipose tissue obtained from foetal lambs at about 120 days of gestation or within 3 days of term, and 9-month-old sheep: the rates of synthesis from glucose of fatty acids, acylglycerol glycerol, pyruvate and lactate; the rate of glucose oxidation to CO2 and the proportions contributed by the pentose phosphate cycle, pyruvate dehydrogenase and the tricarboxylic acid cycle; the activities of hexokinase, glucose 6-phosphate dehydrogenase, phosphofructokinase, pyruvate kinase and pyruvate dehydrogenase. 2. The total rate of glucose utilization was lower in pieces of adipose tissue from near-term lambs than 120-day foetal lambs and the pattern of glucose metabolism differed, with, for example, a much smaller proportion of glucose carbon being used for fatty acid synthesis, whereas a greater proportion of glucose oxidation occurred via the tricarboxylic acid cycle in the near-term lambs. In general, these differences in glucose metabolism were not associated with differences in the activities of the various enzymes listed above. 3. The rates of glucose utilization per fat-cell by 120-day foetal lambs and 9-month-old sheep were very similar but, again, the proportions metabolized to the various products differed. In particular, there was a smaller proportion of glucose oxidized via the pentose phosphate cycle and a greater proportion oxidized via pyruvate dehydrogenase and the tricarboxylic acid cycle in adipose tissue from foetal lambs. These differences were matched by a lower activity of glucose 6-phosphate dehydrogenase and a higher pyruvate dehydrogenase activity in fat-cells from the foetal lambs.
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PMID:Glucose metabolism and its regulation in pieces of perirenal adipose tissue from foetal lambs. 687 Aug 2

To probe the effects of the substrate, glucose, and the cofactor, Mg2+, on the structure of hexokinase (ATP:D-hexose 6-phosphotransferase, EC 2.7.1.1), titrations of the tryptophan fluorescence of yeast hexokinase isozyme P-II(B) were performed. Acrylamide was used as a quenching titrant in the absence and in the presence of glucose and Mg2+ singly and together at pH 5.5 and 8.3 at 20 degrees C. The four tryptophan residues of the monomeric subunit of yeast hexokinase may be classified as two surface residues, one being highly accessible to dissolved I- and one with restricted accessibility to I-, one glucose-quenchable residue in the cleft, and one buried (Kramp, D.C. and Feldman, I. (1978) Biochim. Biophys. Acta 537, 406--416). The acrylamide data were analyzed by least-squares computer analysis for quenching constants and fractional fluorescence values of the tryptophan residues. The quenching constants measure the accessibilities of the residues to the quencher, while the fractional fluorescences are related to the microenvironments of the fluorophores. At each pH value, glucose altered the quenching constants, but not the fractional fluorescence, of the tryptophan residues. Mg2+ greatly accentuated at this glucose effect, especially for the surface residue near the cleft opening. Comparison of acrylamide- and I-quenching data shows that this particular residue has a positively charged microenvironment. A pH change from 5.5 to 8.3 increased the acylamide-accessibility of the cleft tryptophan but did not seem to influence accessibility of the surface residues or the buried residue significantly, thus strengthening our previous conclusion that the cleft opening is small enough at pH 5.5 to partially restrict entrance of organic molecules and negative ions. However, with saturating glucose present there was a pH effect on the surface residue accessibility. Titrations in 55 vol.% glycerol suggest the presence of transient channels (not just holes) in the hexokinase structure, which allows penetration of the protein by solution. Consequently, the buried tryptophan residue is quenched more strongly by dissolved acrylamide than is attributable to diffusion of quencher through the protein matrix.
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PMID:Effects of glucose and magnesium ion on the quenching of yeast hexokinase fluorescence by acrylamide. 700 Jan 90

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

1. The following were measured in adipose-tissue pieces, obtained from 7-9 month-old sheep, before or after the tissue pieces had been maintained in tissue culture for 24 h: the rates of synthesis from glucose of fatty acids, acylglycerol glycerol, pyruvate and lactate; the rate of glucose oxidation to CO(2); the rate of glucose oxidation via the pentose phosphate pathway; the activities of hexokinase, glucose 6-phosphate dehydrogenase, phosphofructokinase, pyruvate kinase, pyruvate dehydrogenase and ATP citrate lyase; the intra- and extra-cellular water content; the concentration of various metabolites and ATP, ADP and AMP. 2. The proportion of glucose carbon converted into the various products in sheep adipose tissue differs markedly from that observed in rat adipose tissue. 3. There was a general increase in the rate of glucose utilization by the adipose-tissue pieces after maintenance in tissue culture; largest changes were seen in the rates of glycolysis and fatty acid synthesis from glucose. These increases are paralleled by an increase in pyruvate kinase activity. There was no change in the activities of the other enzymes as measured, although the net flux through all the enzymes increased. 4. Incubation of fresh adipose-tissue pieces for 2-6h led to an increase in the affinity of pyruvate kinase for phosphoenolpyruvate. 5. The rate of pyruvate production by glycolysis was greater than the activity of pyruvate dehydrogenase of the tissue. 6. The results suggest that both pyruvate kinase and pyruvate dehydrogenase have important roles in restricting the utilization of glucose carbon for fatty acid synthesis in sheep adipose tissue.
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PMID:Regulation of glycolysis and fatty acid synthesis from glucose in sheep adipose tissue. 715 Feb 63

Lipolysis stimulated in perifused isolated fat cells by 0.5 micrometers epinephrine is an ATP-dependent process which can be monitored by measuring the release of glycerol. The stimulated lipolysis is inhibited to 10 micrometers carbonyl cyanide m-chlorophenyl hydrazone (CCCP), an uncoupler of oxidative phosphorylation. If 20-micrometers glucose is continuously present in the perifusion medium during and after treatment with epinephrine and CCCP, the inhibition of the stimulated lipolysis is reversible when the CCCP is discontinued; otherwise it is not readily reversible. Since 20 micrometers 2-deoxyglucose will not substitute for glucose, metabolism of glucose beyond phosphorylation by hexokinase is concluded to be necessary in order to maintain the reversibility of the inhibition of CCCP. Substitution of 10 micrometers succinate for glucose also did not preserve the reversibility of the CCCP inhibition, and there was no significant difference in the amount of decrease of ATP in fat cells incubated with CCCP and epinephrine in the presence of glucose as compared to the decrease observed in the presence of succinate. The mechanism by which glucose maintains reversibility of the inhibition of stimulated lipolysis by CCCP is therefore not clear.
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PMID:The reversible inhibition by carbonyl cyanide m-chlorophenyl hydrazone of epinephrine-stimulated lipolysis in perifused isolated fat cells. 732 56

Aspergillus nidulans wild-type and the extreme carbon catabolite derepressed mutant creAd-30 were characterized with respect to enzyme activities, metabolite concentrations and polyol pools all related to glycolysis, after growth on D-glucose. In the creAd-30 strain the enzymes hexokinase and fructose-6-phosphate reductase showed a two- and threefold increase in activity, respectively, whereas phosphofructokinase and pyruvate kinase activity decreased two- and threefold, respectively, in comparison with the wild-type strain. The most notable changes in metabolite concentrations were that fructose 2,6-bisphosphate and fructose 1,6-bisphosphate showed a 2.5-fold increase, whereas both pyruvate and citrate decreased in the creAd-30. Striking differences were found for the polyol concentrations measured for the two strains tested. Intracellular glycerol and arabitol concentrations were 10-fold higher and erythritol fivefold higher in creAd-30, whereas intracellular trehalose and mannitol were both decreased. The total internal polyol concentration appears to be constant at approximately 700 mumol (g dry wt)-1. All polyols were also detected in high amounts in the culture filtrate of the creAd-30 mutant strain but no extracellular trehalose was found. The overall production of polyols in this strain was therefore much higher than in the wild-type. The high level of polyols produced and the changes in metabolite concentrations in the creAd-30 strain suggest that the differences in enzyme activities result in an altered flow through glycolysis leading to a more rapid formation of polyols which are subsequently secreted.
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PMID:An extreme creA mutation in Aspergillus nidulans has severe effects on D-glucose utilization. 749 42

Intravenous administration of a single dose (100 micrograms/kg bw) of recombinant tumour necrosis factor-alpha (TNF, cachectin) to rats increased the rate of in vitro fatty acid synthesis in interscapular brown adipose tissue (IBAT) from both glucose and alanine, without changes in the oxidation of these substrates to 14CO2. Lactate production and glycerol release were also unaffected by treatment with the cytokine. Additionally, the presence of TNF in the incubation media did not affect fatty acid synthesis, suggesting an indirect effect of the cytokine. The activities of different enzymes of glucose and alanine metabolism such as hexokinase, phosphofructokinase, pyruvate kinase, glucose-6-phosphate dehydrogenase and alanine transaminase, did not suffer changes as a consequence of TNF administration. The same applied to the enzymatic activities involved in fatty acid synthesis such as fatty acid synthase, acetyl-CoA carboxylase and ATP-citrate lyase. Conversely, citrate levels in IBAT were increased in animals treated with TNF, suggesting that it could be the cause for the increased fatty acid synthesis in this tissue.
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PMID:Metabolic effects of tumour necrosis factor-alpha on rat brown adipose tissue. 759 46

Macromolecules as components of the physiological mitochondrial environment were substituted by addition of 10% dextran 70. This led to a significant reduction of the space between the two envelope and the crista membranes and to an increase of contact sites as observed by freeze-fracture analysis. The preferential binding of hexokinase in these sites was employed to further analyze the dextran effect: (i) desorption of the enzyme by digitonin treatment was found to be significantly reduced in the presence of dextran although liberation of adenylate kinase and monoamine oxidase were not affected, (ii) the affinity of isolated hexokinase isozyme I to liver mitochondria was increased by dextran. Generally the binding of hexokinase to intact mitochondria (also control mitochondria) followed a co-operative mechanism and led to an activation. Cooperativity and activation were not observed when the contact formation was suppressed by dinitrophenol or glycerol. The binding of hexokinase to the isolated outer membrane resembled that of mitochondria in the absence of contacts (i.e., no cooperativity and activation). Conversely to the observation in intact mitochondria, dextran rather reduced the affinity of hexokinase to the isolated outer membrane. Kinetic analyses of the dextran effect served to explain the function of contact site specific hexokinase binding. We observed that dextran improved the hexokinase dependent stimulation of the oxidative phosphorylation (state 3 respiration), while the activity of the enzyme with internal or external ATP remained unaffected. The results suggest three things: (i) that contact sites are probably more frequent in the intact cell than in vitro in the absence of macromolecules, (ii) that the contact preference of hexokinase serves rather the ADP supply of the translocator than the ATP transfer to the enzyme and (iii) that the total cellular hexokinase activity may be regulated by specific binding of the enzyme to the contact sites, either because of a different pore structure or because of additional components exclusively exposed in these sites.
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PMID:Effect of macromolecules on the structure of the mitochondrial inter-membrane space and the regulation of hexokinase. 768 6


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