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 energy requirement for protein translocation across membrane was studied with inverted membrane vesicles from an Escherichia coli strain that lacks all components of F1F0-ATPase. An ompF-lpp chimeric protein was used as a model secretory protein. Translocation of the chimeric protein into membrane vesicles was totally inhibited in the presence of carbonyl cyanide m-chlorophenylhydrazone (CCCP) or valinomycin and nigericin and partially inhibited when either valinomycin or nigericin alone was added. Depletion of ATP with glucose and hexokinase resulted in the complete inhibition of the translocation process, and the inhibition was suppressed by the addition of ATP-generating systems such as phosphoenolpyruvate-pyruvate kinase or creatine phosphate-creatine kinase. These results indicate that both the proton motive force and ATP are required for the translocation process. The results further suggest that both the membrane potential and the chemical gradient of protons (delta pH), of which the proton motive force is composed, participate in the translocation process.
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PMID:In vitro translocation of protein across Escherichia coli membrane vesicles requires both the proton motive force and ATP. 302 75

1. The products of the lactoperoxidase-catalysed oxidation of thiocyanate by hydrogen peroxide were sulphate, carbon dioxide and ammonia. Cyanate, sulphite and a compound showing increased extinction at 235mmu (the ;235 compound') were intermediate oxidation products. 2. Two of the intermediates acted as electron acceptors in the oxidation of NADH(2). Thus NADH(2) was oxidized by sulphite in the presence of lactoperoxidase (EC 1.11.1.7) and Mn(2+) and by the ;235 compound' in the presence of an enzyme, the NADH(2)-oxidizing enzyme, present in extracts of lactoperoxidase-resistant streptococci. Sulphur dicyanide also acted as an electron acceptor in the latter reaction. The ;235 compound' was also reduced non-enzymically by sulphite. 3. The glycolysis of lactoperoxidasesensitive streptococci suspended in glucose solution was not inhibited by sulphite, cyanate, cyanide or the ;235 compound' but was inhibited by sulphur dicyanide. The inhibition by 0.1mm-sulphur dicyanide could be reversed, as could that caused by lactoperoxidase, thiocyanate and hydrogen peroxide, by washing the cells or by the addition of a cell-free extract of a lactoperoxidase-resistant streptococcus. 4. The effects of 0.1mm-sulphur dicyanide on catabolic enzymes of resting streptococci were very similar to those of the lactoperoxidase-thiocyanate-hydrogen peroxide system. Thus hexokinase was completedly inhibited, glucose 6-phosphate dehydrogenase and aldolase were partially inhibited and phosphohexokinase was little affected in both cases.
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PMID:The inhibition of streptococci by lactoperoxidase, thiocyanate and hydrogen peroxide. The oxidation of thiocyanate and the nature of the inhibitory compound. 533 6

Inhibitor titration experiments carried out with carboxyatractyloside, oligomycin and rotenone show that in the case of heart mitochondria the membrane-bound ATPase and the respiratory chain are the major factors controlling the rate of oxidative phosphorylation whereas the adenine nucleotide carrier exhibits no control strength. As shown by carboxyatractyloside titration curves under different conditions, the relative importance of the adenine nucleotide carrier depends on the mode of regeneration (F1-ATPase or glucose plus hexokinase) of ADP from ATP exported outside mitochondria, on the total concentration of adenine nucleotides present in the medium and on the mode of limitation of the rate of respiration (cyanide, rotenone, oligomycin or mersalyl). Concomitantly with the inhibition of O2 consumption, carboxyatractyloside brings about a rise in membrane potential. The inverse relationship between the two processes is observed for carboxyatractyloside concentrations ranging between 0.7 and 1.5 nmol per mg protein. Carboxyatractyloside concentrations below and above this range increase the membrane potential without affecting significantly the rate of respiration. Titration experiments aimed at comparing the effects of ADP, carboxyatractyloside and the uncoupler, carbonyl cyanide p-trifluoromethoxyphenylhydrazone, corroborate the conclusion that in heart mitochondria a major limiting factor in oxidative phosphorylation is the capacity of the respiratory chain.
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PMID:Control of oxidative phosphorylation in rat heart mitochondria. The role of the adenine nucleotide carrier. 608

Cells of the aerotolerant anaerobe Giardia lamblia respire in the presence of oxygen. Endogenous respiration is stimulated by glucose but not by other carbohydrates and Krebs cycle intermediates. Endogenous and glucose-stimulated respiration are insensitive to cyanide, malonate, and 2,4-dinitrophenol, but are inhibited by atabrin and iodoacetamide. G. lamblia produces ethanol, acetate and CO2 both aerobically and anaerobically either from endogenous reserves or exogenous glucose. Molecular hydrogen is not produced. The following enzyme activities were detected in homogenates: hexokinase, fructose-biphosphate aldolase, pyruvate kinase, phosphoenolpyruvate carboxykinase, malate dehydrogenase, malate dehydrogenase (decarboxylating), pyruvate synthase, acetyl-CoA synthetase, alcohol dehydrogenase (NADP+), NADH dehydrogenase, NADPH dehydrogenase, NADPH oxidoreductase and superoxide dismutase. The enzymes of energy and carbohydrate metabolism are nonsedimentable (109 000 x g for 30 min). Activities of lactate dehydrogenase, hydrogenase, phosphate acetyltransferase, acetate kinase, citrate synthase, succinate dehydrogenase, fumarate hydratase and catalase were below the limits of detection. The results suggest the occurrence of glycolysis, energy production by substrate level phosphorylation and a flavin, iron-sulfur protein mediated electron transport system as well as the absence of cytochrome mediated oxidative phosphorylation and functional Krebs cycle.
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PMID:Energy metabolism of the anaerobic protozoon Giardia lamblia. 610 7

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

Previous studies with lens dispersions indicated that the rate-limiting step in glycolysis shifts from hexokinase (HK) in the young lens to phosphofructokinase (PFK) in older lenses. Because the concentrations of the complex controlling factor for these enzymes could not be reproduced reliably in homogenates, the question of age-related control of glycolysis was re-examined in intact lenses. Toward this end, the levels of several metabolites of glucose were measured in fresh and incubated clear lenses. Of the substrates measured per fresh lens, only one changed significantly with age; fructose diphosphate was increased. When lenses were incubated in 2 to 12 mM glucose, the lactate production per lens was not significantly different with age. Together these results suggested that the glycolytic mass of the lens was constant with age. In both young and older lenses, increases in glucose in the medium led to increases in both glucose and glucose-6-phosphate in the lens. The lack of corresponding increase in lactate production suggested that the regulatory step lay downstream from HK, probably at PFK. This finding was corroborated by evidence that the initial acceleration of lactate production by the addition of cyanide (the Pasteur effect) was accompanied by decreases in the substrates of PFK, glucose-6-phosphate and fructose-6-phosphate. A secondary disinhibition of HK, as indicated by decreased lens glucose, became apparent after longer incubation with cyanide. This suggested that after disinhibition of PFK, HK became rate-limiting until the level of glucose-6-phosphate fell enough to allow the disinhibition of the latter enzyme as well. Thus PFK seemed to be the primary regulatory step in aerobic glycolysis in lenses of rats from 1 to 12 months of age.
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PMID:Age and the control of glycolysis in the rat lens. 645 26

We have studied the regeneration of adenosine triphosphate (ATP) in the glycolytic pathway in platelets with a 75% reduction in hexokinase (HK) activity and have investigated aggregation and Ca2+ secretion. HK-deficient platelets had a normal glycolytic flux in the resting state, but responded insufficiently to stimulation with thrombin (5 U/ml). In contrast, glycogen contents and glycogenolysis were normal. When the metabolic adenine nucleotides were labeled with 14C-adenine, the patient's platelets showed a normal adenylate energy charge and a normal level of 14C-ATP. However, the inhibitor of mitochondrial energy generation, CN-, induced a weaker fall in 14C-ATP in the patient's platelets than in the controls. Analysis of secretion markers revealed decreased amounts of granule-bound ATP and secretable Ca2+, whereas granule-bound adenosine diphosphate (ADP), beta-thromboglobulin, N-acetyl-beta-D-glucosaminidase, and beta-glucuronidase were within the normal range. Aggregation and Ca2+ secretion induced by 5 U/ml thrombin were normal and were not changed in the presence of inhibitors of mitochondrial and glycogenolytic energy generation. Aggregation was also normal at 0.1 U/ml thrombin and was independent of these inhibitors, but Ca2+ secretion was greatly impaired when mitochondrial and glycogenolytic ATP resynthesis was abolished. These findings indicate that a severe reduction in HK activity causes insufficient acceleration of the glycolytic flux during stimulation with thrombin. This leads to impaired dense granule secretion in conditions where secretion depends on concurrent ATP resynthesis and glycolysis is rate limiting.
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PMID:Platelet functions and energy metabolism in a patient with hexokinase deficiency. 668 46

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

The distribution of hexokinase between bound and soluble forms was studied by digitonin fractionation of Zajdela hepatoma ascites cells maintained under various metabolic conditions. Addition of glucose to Zajdela cells respiring on endogenous substrates induces an immediate inhibition of respiration by 50-60% ( Crabtree effect), and a production of acid due to glycolysis. Acid production decreases abruptly after 60s to 50% of the initial rate. The ATP/ADP ratio is not altered by the addition of glucose or by different rates of glycolysis. The uncoupling agent carbonyl cyanide m-chlorophenylhydrazone decreases the ATP/ADP ratio by 10-fold in cells respiring on endogenous substrate, but has little effect on cells oxidizing glucose. Rapid fractionation of the cells under these various metabolic conditions revealed no change in the distribution of hexokinase. Approx. 75% of hexokinase is bound in all cases, in contrast with lactate dehydrogenase, 95% of which was in the soluble form. Longer-term incubations (to 20 min) revealed only slight (10-15%) increases in soluble hexokinase in cells incubated with glucose. Various metabolic inhibitors had little additional affect on the subcellular distribution of hexokinase. Thus a rapid release of hexokinase from mitochondrial membrane is not a mechanism by which glycolysis is regulated in rapidly growing Zajdela hepatoma.
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PMID:Altered metabolic states do not change the intracellular distribution of hexokinase in Zajdela hepatoma ascites cells. 672 51

The atractyloside-insensitive accumulation of adenine nucleotides by rat liver mitochondria (as opposed to the exchange-diffusion catalysed by the adenine nucleotide translocase) has been measured by using the luciferin/luciferase assay as well as by measuring [14C]ATP uptake. In foetal rat liver mitochondria ATP is accumulated more rapidly than ADP, whereas AMP is not taken up. The uptake of ATP occurs against a concentration gradient, and the rate of ATP uptake is greater in foetal than in adult rat liver mitochondria. The accumulated [14C]ATP is shown to be present within the mitochondrial matrix space and is freely available to the adenine nucleotide translocase for exchange with ATP present in the external medium. The uptake is specific for ATP and ADP and is not inhibited by adenosine 5'-[beta gamma-imido] triphosphate, GTP, CTP, cyclic AMP or Pi, whereas dATP and AMP do inhibit ATP accumulation. The ATP accumulation is also inhibited by carbonyl cyanide m-chlorophenylhydrazone, KCN and mersalyl but is insensitive to atractyloside. The ATP uptake is concentration-dependent and exhibits Michaelis-Menten kinetics. The divalent cations Mg2+ and Ca2+ greatly enhance ATP accumulation, and the presence of hexokinase inhibits the uptake of ATP by foetal rat liver mitochondria. These latter effects provide an explanation for the low adenine nucleotide content of foetal rat liver mitochondria and the rapid increase that occurs in the mitochondrial adenine nucleotide concentration in vivo immediately after birth.
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PMID:The transport and accumulation of adenine nucleotides during mitochondrial biogenesis. 730 14


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