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)

Brain hexokinase (ATP:D-hexose-6-phosphotransferase, EC 2.7.1.1) binds selectively to the outer membrane of rat liver mitochondria but not to inner mitochondrial or microsomal membranes nor to the plasma membrane of human erythrocytes. A protein having subunit molecular weight of 31,000, determined by sodium dodecyl sulfate-gel electrophoresis, has been highly purified from the outer mitochondrial membrane by repetitive solubilization with octyl-beta-D-glucopyranoside followed by reconstitution into membranous vesicles when the detergent is removed by dialysis. When incorporated into lipid vesicles, the protein confers the ability to bind brain hexokinase in a Glc-6-P-sensitive manner as is seen with the intact outer mitochondrial membrane. Hexokinase binding ability and the 31,000 subunit molecular weight protein co-sediment during sucrose density gradient centrifugation. Both hexokinase binding ability and the 31,000 subunit molecular weight protein are resistant to protease treatment of the intact outer mitochondrial membrane while other membrane proteins are extensively degraded. It is concluded that this protein, designated the hexokinase-binding protein (HBP), is an integral membrane protein responsible for the selective binding of hexokinase by the outer mitochondrial membrane.
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PMID:Purification of a hexokinase-binding protein from the outer mitochondrial membrane. 44 25

The genetics of hexokinase (HK) variants in a mosquito, Culex pipiens L., was studied using starch gel electrophoresis. Three isozymic forms of HK, all migrating anodally, were present in all three body regions, but in differing proportions. No obvious differences in specificity for three hexose sugars was detected among the three isozymic bands. However, qualitative differences in staining intensity indicate the following order of substrate affinity: glucose greater than fructose greater than mannose. The inheritance of the HK variants is controlled by a pair of co-dominant alleles at a single genetic locus.
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PMID:The genetics of hexokinase in a mosquito, Culex pipiens. 53 25

We assessed the analytical performance of the co-immobilized hexokinase (EC 2.7.1.1) and glucose-6-phosphate dehydrogenase (EC 1.1.1.49) method for D-glucose analysis on the Technicon SMAC. The enzyme-containing coils were usable for one month, or 12 000 tests. Bilirubin, hemoglobin, lipemia, creatinine, uric acid, citric acid, and ascorbic acid did not interfere. Results with this method were compared to those by the National Glucose Reference Method. The upper limits of the total error estimate (a combination of random and systematic errors) were 76, 74, and 125 mg/liter at concentrations of 500, 1200, and 3000 mg/liter, respectively. The error estimates were less than allowable errors based on medical usefulness; thus the method was judged to perform acceptably with respect to the Reference Method. We also present performance data for the routine SMAC glucose oxidase (EC 1.1.3.4)/Peroxidase (EC 1.11.1.7) 3-methyl-2-benzothianolinone hydrazone-N,N-dimethylaniline method, the direct hexokinase method with the Du Pont aca, and the glucose oxidase oxygen-rate method with the Beckman Glucose Analyzer.
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PMID:Evaluation of the co-immobilized hexokinase/glucose-6-phosphate dehydrogenase method for glucose, as adapted to the Technicon SMAC. 65 1

We have demonstrated previously that in vitro L-sorbose acts directly on dog erythrocytes to induce hemolysis. Here we report that L-sorbose depresses lactate formation in dog hemolysates from glucose, mannose and fructose but not from glucose-6-phosphate and galactose, suggesting that L-sorbose interacts with glycolysis at the level of the hexokinase.
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PMID:Inhibition of glycolysis by L-sorbose in dog erythrocytes. 65 9

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 D-glucose anomeric preference of hexokinases isolated from rat liver, brain, and skeletal muscle, and bovine retina was studied using the glucose-6-phosphate dehydrogenase-NADP system. The ratios of maximum phosphorylation rates of beta-D-glucose to those of alpha-D-glucose were 1.33, 1.46, and 1.54 for hexokinase types I, II, and III from rat liver, 1.45 and 1.63 for type I from rat brain and bovine retina, 1.53 for type II from rat skeletal muscle, and 0.55 (when determined at 5 mM) for type IV (glucokinase) from rat liver, respectively.
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PMID:D-Glucose anomeric preference of hexokinases in higher animals. 71 11

The compounds P1-(adenosine-5')-P3-(glucose-6) triphosphate (Ap3 glucose) and P1-(adenosine-5')-P4-(glucose-6)tetraphosphate (Ap4 glucose) were synthesized as possible transition-state analogs for hexokinase (ATP: D-hexose 6- phosphotransferase, EC 2.7.1.1). Both compounds were inhibitors of this enzyme, competitive against ATP and apparently uncompetitive against glucose. The inhibition constants for Ap3 glucose and Ap4 glucose were 0.43 mM and 0.37 mM, respectively. These results indicate that the inhibitors do not appreciably bind to hexokinase until the glucose binding site is filled. The sugar portion of the inhibitors therefore does not contribute to binding, and the compounds are acting as ATP analogs, Ap3 glucose and Ap4 glucose are also slow substrates for glucose-6-phosphate dehydrogenase.
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PMID:Inhibition of hexokinase by multisubstrate analogs. 83 47

Three glucose-phosphorylating enzymes having different specificities for glucose and fructose were separated from the cell-free extract of Candida tropicalis by means of ammonium sulfate fractionation and chromatography on DEAE-cellulose and Sephadex G-100. Two of them, which phosphorylated fructose 1.5 times faster than glucose, were designated as hexokinase I and II (ATP : D-hexose 6-phosphotransferase, EC 2.7.1.1.), and the other with very low or no fructose-phosphorylating activity, as glucokinase (ATP : D-glucose 6-phosphotransferase, EC 2.7.1.2). Km values for glucose with both hexokinase I and glucokinase were 0.3 mM, and that for fructose with hexokinase I was 2.2 mM. Time-course changes in the levels of these enzymes in C. tropicalis growing on glucose and on n-alkane revealed that hexokinase was induced specifically by the sugars, while glucokinase was a constitutive enzyme. Addition of cycloheximide to the culture medium prevented the increase in the hexose-phosphorylating activity and in the Fru/Glu ratio (the ratio of enzymatic phosphorylation of fructose to that of glucose) in the cells. Although Candida lipolytica also contained hexokinase and glucokinase, both enzymes seemed to be constitutive.
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PMID:Glucose-phosphorylating enzymes of Candida yeasts and their regulation in vivo. 83 48

The uptake and phosphorylation of 2-deoxy-D-glucose by isolated adipocytes of the rat was determined by a method of rapid flotation through oil coupled with separation of sugar from sugar phosphate by chromatography on Dowex-1-formate. Uptake of the sugar is rapid and linear over 5 min, with a gradual decline thereafter; by 1 h, no further uptake is observed. Initially only 2-deoxy-glucose phosphate is observed within the cells; by 1 h, however, free 2-deoxy-glucose accumulates to levels approximately those in the medium. Phosphorylation ceases when intracellular levels of 2-deoxyglucose phosphate are about 50 mM regardless of the medium concentration of 2-deoxyglucose; this does not represent feedback inhibition of hexokinase, since the enzyme in fat cell homogenates is not inhibited by 50 mM 2-deoxyglucose 6-phosphate. Accumulation of deoxyglucose 6-phosphate is associated with a marked decline in intracellular ATP levels. Fat cell respiration is also depressed by approximately 50 per cent after a 1 h preincubation with 10 or 20 mM 2-deoxyglucose. Intracellular ATP levels and O2 uptake are only partially corrected by the addition of pyruvate to the incubation medium. Since no glucose was present in the medium, and intracellular concentrations of glycogen are known to be small in adipose tissue, it is proposed that accumulation of 2-deoxyglucose 6-phosphate within fat cells has a direct inhibitory effect on cell respiration unrelated to inhibition of glycolysis. No increase in intracellular free fatty acids was observed to explain this, and under the conditions of the incubations it is unlikely that Pi availability was rate limiting. The exact locus of inhibition is unknown.
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PMID:Metabolic effects of 2-deoxy-D-glucose in isolated fat cells. 83

Hexokinase from pyloric caeca of the starfish, Asterias amurensis, was purified to a specific activity of 148 units/mg protein. The purified enzyme appeared to be homogeneous on SDS-polyacrylamide gel electrophoresis. The molecular weight determined by SDS polyacrylamide gel electrophoresis and Ultrogel AcA 34 gel filtration was about 50,000. The enzyme showed a broad pH optimum ranging from 7.4 to 9.5. The Km values for D-glucose, D-fructose, 2-deoxy-D-glucose, D-mannose, D-glucosamine and ATP were 0.045, 4, 0.21, 0.05, 0.35 and 0.3 mM, respectively. N-Acetyl-D-glucosamine, D-xylose and D-galactose were not phosphorylated. The enzyme was strongly inhibited by the reaction products, glucose 6-phosphate and ADP, but not by high levels of D-glucose. The starfish hexokinase thus resembled mammalian isozyme A with respect to kinetic properties.
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PMID:Purification and properties of hexokinase from the starfish, Asterias amurensis. 89 76


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