Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.1.1 (hexokinase)
 5,274 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Spirochaeta thermophila RI 19.B1 (DSM 6192) fermented glucose to lactate, acetate, CO2, and H2 with concomitant formation of cell material. The cell dry mass yield was 20.0 g/mol of glucose. From the fermentation balance data and knowledge of the fermentation pathway, a YATP of 9.22 g of dry mass per mol of ATP was calculated for pH-uncontrolled batch-culture growth on glucose in a mineral medium. Measurement of enzyme activities in glucose-grown cells revealed that glucose was taken up by a permease and then subjected to ATP-dependent phosphorylation by a hexokinase. Glucose-6-phosphate was further metabolized to pyruvate through the Embden-Meyerhof-Parnas pathway. The phosphoryl donor for phosphofructokinase activity was PPi rather than ATP. This was also found for the type strain of S. thermophila, Z-1203 (DSM 6578). PPi was probably formed by pyrophosphoroclastic cleavage of ATP, with recovery of the resultant AMP by the activity of adenylate kinase. All other measured kinase activities utilized ATP as the phosphoryl donor. Pyruvate was further metabolized to acetyl coenzyme A with concomitant production of H2 and CO2 by pyruvate synthase. Lactate was also produced from pyruvate by a fructose-1,6-diphosphate-insensitive lactate dehydrogenase. Evidence was obtained for the transfer of reducing equivalents from the glycolytic pathway to hydrogenase to produce H2. No formate dehydrogenase or significant ethanol-producing enzyme activities were detected.
 ...
PMID:Glucose catabolism by Spirochaeta thermophila RI 19.B1. 155 64

It has been shown previously that glucose-induced insulin release is completely absent in rat pancreatic islets that had been cultured for 1 day at low glucose (1 mM) and that it is restored by culturing islets for a 2nd day at high (20 mM) glucose (MacDonald, M. J., Fahien, L. A., McKenzie, D. I., and Moran, S. M. (1991) Am. J. Physiol. 259, E548-E554). It has been suggested that the incapacitation of glucose's insulinotropism is due to down-regulation of the synthesis of enzymes that process glucose's metabolic signal for insulin release. In the current study, results of metabolic, enzymic, and molecular biologic experiments were each consistent with (an) intramitochondrial site(s) of down-regulation in islets cultured at low glucose. Glucose metabolism was inhibited 80% in islets cultured at 1 mM glucose. The suppression of release of 14CO2 from [6-14C]glucose greater than from [U-14C]glucose greater than [3,4-14C]glucose greater than from [1-14C]glucose in islets cultured at low glucose indicated a mitochondrial site of down-regulation because C-6 of glucose can only be converted to CO2 in the citric acid cycle, whereas C-1 can be released as CO2 in the 6-phosphogluconate dehydrogenase [corrected] reaction, and C-6 of glucose dwells in the citric acid cycle longer than carbons 2-5 of glucose. Since carbons 3 and 4 of glucose can be decarboxylated in the pyruvate dehydrogenase reaction, incomplete suppression of CO2 formation from these carbons is consistent with suppression of pyruvate carboxylation as well as decarboxylation. Formation of 3HOH from [5-3H]glucose was equal in the two groups of islets, indicating that glycolysis as far as phosphoenolpyruvate was intact. This idea was supported by assays which showed that activities of enzymes of the glycolytic pathway between glucokinase/hexokinase and pyruvate kinase were equal in both types of islets. Additional studies indicated that regulation by glucose was at transcription of genes coding for some mitochondrial enzymes. Glucokinase, malic enzyme, and fumarase mRNAs were not affected by glucose, whereas the pyruvate dehydrogenase E1 alpha subunit and pyruvate carboxylase mRNAs were decreased 85-90% in islets cultured at 1 mM glucose. Pyruvate dehydrogenase enzyme activity was decreased to a similar extent in these islets. About 24 h was required for maximal (de)induction of pyruvate dehydrogenase E1 alpha and pyruvate carboxylase mRNAs, and the amounts of transcripts were proportional to the concentrations of glucose between 1 and 20 mM.(ABSTRACT TRUNCATED AT 400 WORDS)
 ...
PMID:Pyruvate dehydrogenase and pyruvate carboxylase. Sites of pretranslational regulation by glucose of glucose-induced insulin release in pancreatic islets. 193 63

1. Transport and accumulation of 2-deoxy-D-glucose (2dGlc) in rat and murine peritoneal macrophages were investigated by using C-1-3H-labelled and C-2,6-3H-labelled 2dGlc. 2. There was active accumulation of both C-1- and C-2,6-labelled 2dGlc by quiescent rat and murine macrophages via a phloretin-inhibitable transport system. 3. The rate of uptake and accumulation of 2dGlc (C-1 label) was increased by exposure to human macrophage colony-stimulating factor (mCSF-1) (1000 units/ml) in both murine and rat macrophages. This indicates that mCSF-1 enhances coupling between hexokinase activity and glucose transport at the endofacial surface of the transporter. 4. Phorbol 12-myristate 13-acetate ('phorbol') at 40 nM stimulated 2dGlc in rat macrophages entirely by increasing the C-2,6 label uptake. This indicates that phorbol stimulates 2dGlc uptake mainly by increasing the activity of the pentose phosphate pathway. 5. Simultaneous exposure to phorbol and mCSF-1 stimulates 2dGlc uptake to a greater extent than found with either phorbol or mCSF-1 alone. This result is explained by a simultaneous enhancement of pentose phosphate-pathway activity and of hexokinase activity acting at the endofacial surface of the cell membrane. The dual activation of these serial processes coupled to the loss of the reaction products of the pentose phosphate-shunt pathway from the cells in the form of reactive oxygen intermediates, protons and CO2 could explain the synergistic action of phorbol and mCSF-1 in activation of sugar transport in macrophages.
 ...
PMID:Synergistic activation of 2-deoxy-D-glucose uptake in rat and murine peritoneal macrophages by human macrophage colony-stimulating factor-stimulated coupling between transport and hexokinase activity and phorbol-dependent stimulation of pentose phosphate-shunt activity. 240 38

Erythrocytes were separated by age using a combination of density centrifugation and counterflow centrifugation and tested for basal activity of the hexose monophosphate shunt (HMP-shunt) as well as the methylene blue-stimulated maximal capacity by measuring CO2 production. No significant differences were found in basal HMP-shunt activity, but the maximal methylene blue-stimulated activity of old erythrocytes reached only half of the activity of the total cell population. The maximal HMP-shunt activity showed a significant correlation with hexokinase activity, but not with glucose-6-phosphate dehydrogenase activity in all but the youngest cells. The sensitivity to oxidative stress was tested by measuring the kinetics of pyruvate kinase isolated from erythrocytes incubated in presence and absence of methylene blue. Pyruvate kinase kinetics were affected more in the old cell population than in the total cell population: the K0.5 for phosphoenol-pyruvate increased four times in the unseparated cells and eight times in old cells.
 ...
PMID:Hexose monophosphate shunt activity in erythrocytes related to cell age. 261 18

A simple and cheap one-step enzymatic method has been developed for the determination of 1-14C-glucose in plasma. C-1 of glucose is cleaved off as CO2 by treatment with hexokinase, glucose-6-phosphate dehydrogenase, and 6-phosphogluconic dehydrogenase. True 1-14C-glucose activity is then calculated as the difference between total radioactivity and radioactivity remaining after enzyme treatment and evaporation. The reaction is shown to be quantitative and specific, thus eliminating both labelled metabolites and label recycled to other positions in glucose. Two different types of pig experiments show that 1-14C-glucose, when determined by this method, is as irreversible a tracer as the commonly used 3-3H-glucose.
 ...
PMID:Enzymatic determination of 1-14C-glucose in pig plasma. 267 67

The effect of lonidamine (LND), 1-(2,4-dichlorobenzyl)-1H-indazol-3 carboxylic acid, on the utilization of carbon from 14C-labeled glucose by cell cultures of the permanent strain LI derived from a human glioblastoma multiforme (astrocytoma) has been investigated. The results may be summarized as follows. Aerobic glycolysis is the main energy-yielding process as shown by the fact that the greatest part of glucose carbon atoms is incorporated into lactate. Nevertheless, the amount of glucose converted accounts for only 63% of the lactate produced, indicating the presence of an elevated endogenous aerobic glycolysis. The amount of glucose carbon atoms incorporated into CO2, lipids, nucleic acid, and supporting structures is low. LND decreased the incorporation of 14C activity in all the above mentioned isolated compounds because of its ability to inhibit glucose phosphorylation. Consequently, there is a lower concentration of glucose-6-phosphate which, in turn, affects the rate of formation of several metabolites in glycolytic and pentose phosphate pathways. Experiments with [1-14C]-2-deoxy-D-glucose further substantiate the idea of glucose phosphorylation as a main target of LND and strongly suggest the presence of a mitochondrially bound hexokinase. The higher inhibition of glucose phosphorylation in exponentially growing cells indicates a further shift of the enzyme toward mitochondria-bound form and confirms the importance of the energy status of the cell in eliciting the response to LND. The reduced capacity of LND-treated cells to synthetize ATP and glucose-6-phosphate reflects the decreased synthesis of proteins and nucleic acids, which affects cell growth and duplication.
 ...
PMID:Effect of lonidamine on the utilization of 14C-labeled glucose by human astrocytoma cells. 282 Jul 86

Energy metabolism in proliferating cultured rat thymocytes was compared with that of freshly prepared non-proliferating resting cells. Cultured rat thymocytes enter a proliferative cycle after stimulation by concanavalin A and Lymphocult T (interleukin-2), with maximal rates of DNA synthesis at 60 h. Compared with incubated resting thymocytes, glucose metabolism by incubated proliferating thymocytes was 53-fold increased; 90% of the amount of glucose utilized was converted into lactate, whereas resting cells metabolized only 56% to lactate. However, the latter oxidized 27% of glucose to CO2, as opposed to 1.1% by the proliferating cells. Activities of hexokinase, 6-phosphofructokinase, pyruvate kinase and aldolase in proliferating thymocytes were increased 12-, 17-, 30- and 24-fold respectively, whereas the rate of pyruvate oxidation was enhanced only 3-fold. The relatively low capacity of pyruvate degradation in proliferating thymocytes might be the reason for almost complete conversion of glucose into lactate by these cells. Glutamine utilization by rat thymocytes was 8-fold increased during proliferation. The major end products of glutamine metabolism are glutamate, aspartate, CO2 and ammonia. A complete recovery of glutamine carbon and nitrogen in the products was obtained. The amount of glutamate formed by phosphate-dependent glutaminase which entered the citric acid cycle was enhanced 5-fold in the proliferating cells: 76% was converted into 2-oxoglutarate by aspartate aminotransferase, present in high activity, and the remaining 24% by glutamate dehydrogenase. With resting cells the same percentages were obtained (75 and 25). Maximal activities of glutaminase, glutamate dehydrogenase and aspartate aminotransferase were increased 3-, 12- and 6-fold respectively in proliferating cells; 32% of the glutamate metabolized in the citric acid cycle was recovered in CO2 and 61% in aspartate. In resting cells this proportion was 41% and 59% and in mitogen-stimulated cells 39% and 65% respectively. Addition of glucose (4 mM) or malate (2 mM) strongly decreased the rates of glutamine utilization and glutamate conversion into 2-oxoglutarate by proliferating thymocytes and also affected the pathways of further glutamate metabolism. Addition of 2 mM-pyruvate did not alter the rate of glutamine utilization by proliferating thymocytes, but decreased the rate of metabolism beyond the stage of glutamate significantly. Formation of acetyl-CoA in the presence of pyruvate might explain the relatively enhanced oxidation of glutamate to CO2 (56%) by proliferating thymocytes.
 ...
PMID:Glutamine and glucose metabolism during thymocyte proliferation. Pathways of glutamine and glutamate metabolism. 286 9

A major difference between the metabolism of Leishmania species amastigotes and cultured promastigotes was found in the area of CO2 fixation and phosphoenolpyruvate metabolism. Malate dehydrogenase (EC 1.1.1.37) and phosphoenolpyruvate carboxykinase (EC 4.1.1.49) were at much higher activities in amastigotes than promastigotes of both L. m. mexicana and L. donovani, whereas the reverse was true of pyruvate kinase (EC 2.7.1.40). Pyruvate carboxylase (EC 6.4.1.1) and malic enzyme (carboxylating) (EC 1.1.1.40) could not be detected in L. m. mexicana amastigotes. Promastigotes of L. m. mexicana had a high NAD-linked glutamate dehydrogenase activity in comparison to amastigotes, whereas NADP-linked glutamate dehydrogenase activity was detected only in amastigotes. Leishmania m. mexicana culture promastigotes were killed in vitro by the trivalent antimonial Triostam (LD50, 20 micrograms/ml) and the trivalent arsenical melarsen oxide (LD50, 20 micrograms/ml), but they were unaffected by Pentostam. Neither antimonial drug significantly inhibited leishmanial hexokinase (EC 2.7.1.2), phosphofructokinase (EC 2.7.1.11), pyruvate kinase, malate dehydrogenase or phosphoenolpyruvate carboxykinase, whereas melarsen oxide was a potent inhibitor of all the enzymes tested except phosphoenolpyruvate carboxykinase.
 ...
PMID:Leishmania mexicana: enzyme activities of amastigotes and promastigotes and their inhibition by antimonials and arsenicals. 298 38

We propose the following scheme for cerebral uptake and overall metabolism of glucose in vivo: that brain selects from two pools of glucose anomers in arterial blood, that it takes up excess glucose, that glucose enters the brain tissue as glucose-6-phosphate through the actions of mutarotase and hexokinase, that some glucose-6-phosphate becomes metabolized to CO2 and some becomes incorporated into brain carbon pools, and that excess glucose-6-phosphate leaves brain through glucose-6-phosphatase and mutarotase activities. This results from our observations in arterio-venous studies for the determination of cerebral metabolism in humans in vivo that the cerebral uptake of [14C]glucose often appeared to differ from that of unlabeled glucose. With rapidly falling arterial radioactivity, unlabeled glucose uptake was more than [14C]glucose. With rising arterial radioactivity, [14C]glucose extraction exceeded unlabeled glucose. Studies with [14C]glucose-6-phosphate suggested that glucose-6-phosphatase in brain removes excess substrate by dephosphorylation. However, when arterial [14C]glucose increased slowly, [14C]glucose uptake varied considerably and the data resembled human cerebral metabolism of glucose anomers. An experiment employing [13C]glucose and NMR provided further support for our proposed scheme.
 ...
PMID:Evidence for the cerebral uptake in vivo from two pools of glucose and the role of glucose-6-phosphatase in removing excess substrate from brain. 298 20

Synaptosomes prepared and incubated in a variety of ways from rat cerebra exhibited intractable, unphysiologically low adenylate energy charge values (approximately 0.37-0.60), low total adenine nucleotide contents (approximately 8-10 nmol/mg protein), and much higher adenylate kinase apparent Keq values (approximately 3-8) as compared to intact brain tissue (values of approximately 0.90, 25 nmol/mg, and 0.74, respectively). Synaptosomes prepared from mouse, dog, and chicken cerebra had values essentially identical to those from rat. When incubated under oxygen in a physiological salt solution containing glucose, synaptosomes metabolized more glucose to lactic acid than to CO2, and the addition of 100 microM veratridine caused a two- to threefold stimulation of O2 uptake, lactate accumulation, and CO2 output. It is known that synaptosome fractions contain a substantial number (at least 30-45% by volume) of cytoplasm-containing particles devoid of mitochondria (henceforth termed "cytosolic particles"), and that approximately 80% of brain hexokinase is bound to the outer mitochondrial membrane. For the cytosolic particles, lacking oxidative phosphorylation, to maintain their "in vivo" ATP turnover would require about a 19-fold increase in the glycolytic rate, which is not possible due to limiting amounts of hexokinase, and thus these particles are postulated to be responsible for the high level of aerobic lactate accumulation and the intractable low energy charge values found in synaptosome fractions. The mitochondria-containing particles are postulated to have a normal energy charge, a submaximal glycolytic rate, and minimal lactate production, on the basis of the capacity of veratridine to stimulate synaptosomal O2 uptake and CO2 and lactate output. Calculations based on this "two populations of particles" hypothesis indicate that for synaptosome fractions in general, (1) the cytosolic particles contain approximately 35-64% of the total adenine nucleotides and maintain an energy charge of approximately 0.12; (2) the cytosolic particles and mitochondria-containing particles have adenylate kinase apparent Keq values of approximately 0.21-1.66 and 0.74, respectively, revealing that the higher apparent Keq values of the synaptosome fractions probably are not real departures from equilibrium: and (3) approximately 31-45% of synaptosome fraction protein is contained in debris, which, when taken into account, yields total adenine nucleotide contents in the cytosolic particles and mitochondria-containing particles of approximately 15-24 and approximately 11-19 nmol/mg of particle protein, respectively.
 ...
PMID:Intractable unphysiologically low adenylate energy charge values in synaptosome fractions: an explanatory hypothesis based on the fraction's heterogeneity. 309 Feb 2


<< Previous 1 2 3 4 5 6 7 8 Next >>