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)

Detailed time courses of uptake of labeled 3-O-methyl-D-glucose and 2-deoxy-D-glycose by untreated and ATP-depleted Novikoff rat hepatoma cells were determined as function of concentration (0.2-10 mM) by a rapid mixing/sampling technique which allows uptake measurements in time intervals as short as 1.5 seconds. Intracellular accumulation of 3-O-methylglucose in untreated and ATP-depleted cells and of deoxyglucose in ATP-depleted cells to equilibrium followed pseudo-first order kinetics and initial velocities were computed from overall time courses of substrate accumulation. Initial velocity was a Michaelis-Menten function of exogenous substrate concentration. The estimated kinetic constants for zero-trans transport of 3-O-methylglucose were about the same for untreated and ATP-depleted cells (Kztm = 1.73 +/- 0.24 mM; Vztmax = 28.8 +/- 3.6 pmoles/microliter cell H2O. sec) and were similar to those for deoxyglucose transport in ATP-depleted cells (Kztm = 0.65 +/- 0.1 mM; Vztmax = 19.6 +/- 1.6 pmoles/microliter cell H2O. sec). Similar kinetic parameters were obtained for the transport of D-glucose and D-galactose in ATP-depleted cells. The transport of 3-O-methylglucose and deoxyglucose were inhibited by each other in a simple competitive manner with apparent Ki's similar to their transport Km's. In untreated cells, in which deoxyglucose was phosphorylated, intracellular steady-state levels of free deoxyglucose accumulated within 10 to 20 seconds of incubation regardless of its concentration in the medium. Thereafter, the rate of deoxyglucose incorporation into total cell material reflected the rate of phosphorylation rather than the transport rate. The rate of deoxyglucose transport exceeded the initial rate of its phosphorylation by 20-40 %. The intracellular steady-state-levels observed during the first 2 minutes of incubation decreased from about 40% of equilibrium level at 0.2 mM deoxyglucose to about 8% at 10 mM. Computer fits of a kinetic equation describing transport and phosphorylation as independent processes operating in tandem to these data are consistent with the observed kinetic constants for hexose transport and hexokinase activity with deoxyglucose as substrate. Upon longer incubation (2-10 minutes) the rate of deoxyglucose uptake by the phosphorylating cells decreased progressively, concomitant with a decrease in intracellular ATP and an increase in intracellular deoxyglucose to equilibrium levels. It is demonstrated that the rate of deoxyglucose uptake, measured at two or more minutes, seriously underestimates the hexose transport rate and yields misleading conclusions regarding the extent and type of inhibition by transport inhibitors, such as persantin or cytochalasin B. Persantin inhibited hexose transport in a simple non-competitive manner (Ki = 20 muM) indicating that the drug affects the function of the hexose carrier.
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PMID:Deoxyglucose and 3-O-methylglucose transport in untreated and ATP-depleted Novikoff rat hepatoma cells. Analysis by a rapid kinetic technique, relationship to phosphorylation and effects of inhibitors. 67 Mar 3

The intraperitoneal (IP) treatment of rats with diazinon (40 mg/kg) resulted in a variety of changes in the brain. Glycogen was depleted, but there was an increase in the activities of glycogen phosphorylase, phosphoglucomutase, hexokinase, lactate dehydrogenase, and fructose 1,6 diphosphatase. The activity of glucose-6-phosphatase was unaffected while that of cholinesterase was significantly reduced. Lactic acid content was increased, while that of pyruvate was not altered. Animals developed tremors and convulsions, which were maximal two hours after treatment. The induced changes may be compensatory mechanisms to provide extra energy to cerebral tissue as a result of the stimulatory effects in diazinon-treated animals.
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PMID:Cerebral glucose and glycogen metabolism in diazinon-treated animals. 350 78

Effect of diazinon (10,20 and 40 mg/kg, i.p.) on the level of blood glucose in rats was investigated. Hyperglycaemia peaked 2 h after i.p. treatment with 40 mg/kg diazinon. The cerebral acetylcholinesterase activity was significantly reduced. The blood level of pyruvic acid was unchanged while that of lactic acid was significantly increased. Convulsions and biochemical changes caused by diazinon (40 mg/kg) were prevented by diazepam injected immediately after diazinon. In diazinon-treated hyperglycaemic animals, the glycogen content of the brain was depleted, the activities of glycogen phosphorylase, phosphoglucomutase and hexokinase were significantly increased and the activity of glucose-6-phosphatase remained unchanged. Lactate dehydrogenase activity was also increased by treatment with diazinon. The induced changes may compensate for the energy requirement of stimulatory effects caused by diazinon.
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PMID:Changes in cerebral glycogenolysis and related enzymes in diazinon treated hyperglycaemic animals. 362 68

Regulation of gene expression by nutrients is an important part of the mechanisms allowing mammals to adapt to their nutritional environment. This is especially true for enzymes involved in the storage of energy such as the lipogenic and glycolytic enzymes in the liver and adipose tissue. We review in the present paper the cellular and molecular mechanisms involved in the regulation of glycolytic and lipogenic enzyme gene expression by glucose. In vivo and in vitro experiments have demonstrated that FAS and ACC gene expression is upregulated by glucose in adipose tissue, FAS, ACC and L-PK expression in the liver and ACC and L-PK expression in a pancreatic beta-cell line. This regulation involves the stimulation of their transcription. In order for glucose to act as a gene inducer, it must be metabolized. In adipose tissue, insulin increases indirectly the expression of FAS and ACC by stimulating glucose metabolism through its well-known effect on glucose transport. In the liver, the action of insulin is also indirect by allowing the expression of glucokinase and hence by increasing glucose metabolism. In the liver, fructose has a potentiating effect on the stimulation of gene expression by glucose through its stimulatory effect on glucokinase activity. Several evidences suggest that glucose-6-phosphate is the signal metabolite: (i) the effect of glucose is mimicked by 2-deoxyglucose (a glucose analogue whose metabolism stops after its phosphorylation by hexokinase) in adipose tissue and beta-cell line but not in the liver in which 2-deoxyglucose-6-phosphate does not accumulate, (ii) intracellular glucose-6-phosphate concentration varies in parallel with ACC, FAS and L-PK mRNA concentrations in liver, adipose tissue and beta-cell line, (iii) in vivo, the kinetics of hexose-phosphate fits with the time-related pattern of gene induction. Glucose response elements have been characterized on three genes, L-PK, S14 (a gene which codes for a protein of unknown function but which is directly related to lipogenesis) and FAS. These glucose response elements have all in common the presence of a sequence 5'-CACGTG-3' which binds a transcription factor of the basic domain, helix-loop-helix, leucine zipper family called USF/MLTF, although the organization of the overall glucose response element probably differs from one gene to another. The mechanisms linking glucose-6-phosphate to the glucose responsive transcription complex are presently largely unknown.
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PMID:Regulation of lipogenic enzyme expression by glucose in liver and adipose tissue: a review of the potential cellular and molecular mechanisms. 886 48

Mitochondria in saponin-skinned cardiac fiber bundles were reported to have an order of magnitude lower apparent affinity to ADP than isolated mitochondria. Although ADP was measured outside the bundles, it was thought that the low affinity was not caused by diffusion gradients because of relatively short diffusion distances. Here we test the hypothesis that considerable ADP diffusion gradients exist and can be diminished by increasing the intrafiber ADP production rate. We increased the ADP-producing activity in rat heart skinned fiber bundles by incubating with 100 IU/ml yeast hexokinase and glucose. Consequently, we observed a significant decrease of the apparent Michaelis constant (K(m)) to ADP of the respiration rate of bundles from 216 +/- 59 to 50 +/- 9 microM. Fitting the results with a mathematical model, we estimated the K(m) of mitochondria in the bundles to be 25 microM. We conclude that the affinity to ADP of in situ mitochondria in heart is of the same order of magnitude as that of isolated mitochondria.
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PMID:High K(m) of oxidative phosphorylation for ADP in skinned muscle fibers: where does it stem from? 1217 31

1. The rate of reaction of mustard gas (H) with thirteen proteins has been determined. The extreme variation in reaction rates is about 100:1. 2. No qualitative difference in the results was observed when the treatment with H was carried out by the Dixon or stirring methods. 3. The kinetics have been analyzed and a bimolecular equation derived which fits the facts. 4. The carboxyl groups of all proteins reacted when the reaction with H was carried out at pH 6.0 in M/25 acetate buffer. In most cases the number of carboxyl groups covered was approximately equal to the number of H residues bound. 5. The amino groups of proteins failed to react with the possible exception of yeast hexokinase. 6. The color obtained when proteins were mixed with Folin's phenol reagent at pH 8.0 decreased as the protein was treated with H. The color returned on treatment of the H-protein with alkali and many of the combined H groups were hydrolyzed. Similar results were observed when a concentrated glycyltyrosine solution was treated with H.
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PMID:REACTION OF ENZYMES AND PROTEINS WITH MUSTARD GAS (BIS(beta-CHLOROETHYL)SULFIDE). 1987 86