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 regulation of intracellular calcium uptake and release in cultured gastric smooth muscle cells was studied in saponin-permeabilized cells derived from the rabbit antrum. Cells were studied in an ATP-regenerating medium in which the value of the ATP-to-ADP ratio was fixed by variation of the relative concentrations of creatine and creatine phosphate in the presence of a constant concentration of adenine nucleotides and creatine kinase. Free calcium in the medium was measured through the use of the fluorescent probe fura-2. As the ratio of ATP/ADP was increased (8.5, 55.0, and 155.0), the rate of calcium sequestration was increased, resulting in a decrease of steady-state free calcium (275.2, 178.4, and 98.1 nM, respectively). The addition of glucose (5 mM) and hexokinase (15 U/ml), which results in an increase of ADP due to the phosphorylation of glucose in the medium, caused an increase of free calcium concentration to a new set point of approximately 400 nM. Mitochondrial blockade with antimycin A before permeabilization had no effect on calcium sequestration or the resultant free calcium concentration, indicating that under physiological conditions calcium is sequestered predominantly into nonmitochondrial storage sites. Specific variation of ATP/ADP had no effect on the concentration dependence of inositol trisphosphate-induced calcium efflux, suggesting the functional independence of intracellular calcium influx and efflux pathways. These results indicate a significant role for cytoplasmic ATP/ADP in the control of intracellular calcium sequestration and the regulation of steady-state calcium concentration in cultured gastrointestinal smooth muscle cells.
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PMID:ATP-dependent control of steady-state cytosolic calcium in cultured gastric smooth muscle. 192 49

To study the mechanical properties of various crossbridge states in the anterior byssus retractor muscle (ABRM) of Mytilus, the tension response of the glycerinated ABRM to a step increase of the length was examined in rigor solutions with saturating Ca2+ (Rca) and without added Ca2+ (R), rigor ones with ADP (AD) and with both ADP and saturating Ca2+ (ADca), and a low ATP, activating one. The application of ADca to a rigor ABRM caused a slow tension development of less than 0.083 kg/cm2 (n = 6) probably because of contaminant ATP in the presence of 0.25 mM p,p-di(adenosine-5')pentaphosphate (Ap5A) and 10 U/ml hexokinase with 2 mM glucose. The instantaneous stiffness in ADca was slightly smaller than that in the low ATP solution and greater than those in R, Rca, and AD, giving evidence that the stretch response reflected the mechanical property of the crossbridges. The rate of the tension decay during the initial 5 ms after the length change was completed was slowest in the ADca among the solutions examined, while during the initial 30-90 ms it was faster in the low ATP solution than R, Rca, AD, and ADca with little difference of the rate in the latter four solutions. The difference in the time course of the tension decay in between the low ATP solution and ADca may be taken to indicate that the high stiffness in ADca was not due to the formation of the tension-generating crossbridges but to the crossbridges with both bound Ca and ADP (AMCaADP) made directly from the rigor crossbridge (AM). Consequently, it was thought that AMCaADP was stiffer than AM and the crossbridges with either bound Ca (AMCa) or ADP (AM.ADP), the latter three kinds of the crossbridges being formed directly from AM, not as a result of ATP hydrolysis.
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PMID:Effects of calcium and ADP on tension responses to step length increases in glycerinated Mytilus smooth muscle. 196 Aug 88

A method was developed for preparation of dansylated derivatives of adenine nucleotides characterized by fluorescence when being irradiated with UV-light. The involvement of dansylated ATP, ADP and AMP as substrate analogues in energy metabolism is demonstrated in the ATPase, hexokinase, pyruvate kinase and adenylate kinase reactions. The kinetics of the reactions is discussed.
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PMID:[Preparation and isolation of dansyladenylates as fluorescent substrates in reactions of the energy metabolism]. 214 Aug 94

The rate of respiration of isolated mitochondria was set at different values by addition of either oligomycin or an ADP-regenerating system (glucose and different amounts of hexokinase). We measured the relationship between respiration rate and membrane potential as respiration was titrated by the addition of malonate under each condition. We used the flux control summation and connectivity theorems and the branching theorem of metabolic control theory to calculate the control over respiration rate exerted by the respiratory chain (and associated reactions), phosphorylating system (and associated reactions) and proton leak at each respiration rate. The analysis also yielded the flux control coefficients of these three reactions over phosphorylation rate and proton leak rate and their concentration control coefficients over protonmotive force. We found that respiration rate was controlled largely by the proton leak under non-phosphorylating conditions, by the phosphorylating system at intermediate rates and by both the phosphorylating system and the respiratory chain in state 3. The rate of phosphorylation was controlled largely by the phosphorylating system itself in state 4 and at intermediate rates, while state 3 control was shared between the phosphorylating system and the respiratory chain; the proton leak had insignificant control. In all states the phosphorylating system had large negative control over the proton leak; the chain and the proton leak both had large positive control coefficients. The protonmotive force was controlled by the chain and by the phosphorylating system; the proton leak had little control.
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PMID:Analysis of the control of respiration rate, phosphorylation rate, proton leak rate and protonmotive force in isolated mitochondria using the 'top-down' approach of metabolic control theory. 215 98

1. Oxygen consumption was investigated in two cultured subpopulations of either undifferentiated (Glc+ cells) or differentiated (Glc- cells) HT29 colon cancer cells and in the corresponding isolated mitochondria. In Glc+ cells, a decrease of the respiration is induced by the presence of glucose (Crabtree effect), whereas it is not the case in Glc- cells. 2. The oxidative phosphorylation rate of Glc- mitochondria is found to be much higher than that of Glc+ mitochondria, due to a higher efficiency to oxidize glutamine, glutamate, 2-oxoglutarate, succinate or malate. 3. In both types of mitochondria, respiration can be supported by the ADP formed by adenylate kinase or nucleotide diphosphate kinase, and, although to a lesser extent in Glc- mitochondria, by hexokinase. 4. Glc+ cells are characterized by a low respiration capacity and a high glycolytic flux leading to the Crabtree effect. Glc- cells are characterized by a better correlation between a moderate glycolytic flux and a high respiratory capacity.
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PMID:Respiration of mitochondria isolated from differentiated and undifferentiated HT29 colon cancer cells in the presence of various substrates and ADP generating systems. 215 27

Interleukin-1 beta (IL-1 beta) has been implicated in the pathogenesis of insulin-dependent diabetes mellitus. In the present study we have investigated the effects of IL-1 beta on glucose metabolism in clonal HIT-T15 beta cells. In the short-term (1 h), 25 U/ml IL-1 beta significantly increased the rates of insulin release and glucose utilisation, but not glucose oxidation. In contrast, after 48 h, IL-1 beta inhibited insulin release and glucose utilisation and oxidation. By assaying enzymes (hexokinase, glucokinase, pyruvate dehydrogenase, glucose 6-phosphatase) and nucleotides (ATP, ADP) associated with the regulation of glycolysis and glucose oxidation, we conclude that the inhibitory effects of IL-1 beta may be due to impaired glucokinase activity.
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PMID:Interleukin-1 beta inhibits glucokinase activity in clonal HIT-T15 beta-cells. 219 15

The possible relevance of D-glucose phosphorylation by mitochondria-bound hexokinase to the control of respiration was examined in mitochondria prepared from either tumoral pancreatic islet cells (RINm5F line) or normal rat liver. In both systems, ATP generated by mitochondria exposed to ADP and succinate could serve as a substrate for the phosphorylation of D-glucose. However, after exposure to exogenous ADP in the presence of succinate, only mitochondria isolated from RINm5F cells displayed a sizeable increase in O2 consumption in response to a subsequent administration of D-glucose. In this respect, the discrepancy between mitochondria from islet cells and liver, respectively, was found to be attributable to the much lower hexokinase activity, relative to respiratory rate, in liver than in RINm5F cell mitochondria. It is speculated that the coupling between hexose phosphorylation and respiration in islet cells may prime the mitochondria to generate ATP during the early metabolic and secretory response to a rise in extracellular D-glucose concentration.
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PMID:Hexose metabolism in pancreatic islet cells: the coupling between hexose phosphorylation and mitochondrial respiration. 220 46

The rate of ATP formation from ADP by adenylate kinase is known to be easily followed by determination of the increase in fluorescence due to the NADPH that is formed by combined reactions of hexokinase and gluc-6-p dehydrogenase. We found that the rate of CTP formation from CDP also can be followed similarly by use of more units of hexokinase and extension of the reaction time. A crude enzyme sample containing most of the activity of adenylate kinase was prepared from pig brain and eluted from a CM-cellulose column. Enzymatic activity of ATP formation and that of CTP formation were compared for all the fractions. Two fractions were found in the eluate; one was rather specific for ADP as substrate, and the other was less specific for ADP and could form CTP at an appreciable rate.
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PMID:Multiple forms of adenylate kinase in pig brain. 224 94

A 50-amino acid peptide predicted by chemical modification studies of yeast hexokinase to contain an ATP-binding site has been synthesized and purified. The peptide, which includes residues from glutamate 78 at the NH2-terminal end to leucine 127 at the COOH-terminal, resides within the smaller of the two lobes found in the three-dimensional structure of yeast hexokinase. It is this region which has been reported recently to exhibit significant sequence homology with hexokinase types I and IV of higher eukaryotic cells and sequence homology with the active site of protein kinases. Similar to native yeast hexokinase, the 50-amino acid peptide interacts strongly with the fluorescent analog TNP-ATP [2',(3')-O-(2,4,6-trinitrophenyl)-adenosine-5'-triphosphate]. A 5-fold enhancement is observed when 8 microM peptide interacts with 20 microM TNP-ATP. The stoichiometry of binding is very close to 1 mol of TNP-ATP/mol peptide. Also, similar to native yeast hexokinase, the fluorescent enhancement observed upon TNP-ATP binding to the synthetic peptide is greater than that observed upon TNP-ADP binding. Finally, TNP-AMP exhibits a much lower fluorescent enhancement in the presence of hexokinase or the synthetic peptide. The additional findings that ATP can readily prevent TNP-ATP binding and that TNP-ATP can substitute for ATP as a weak substrate for hexokinase in the phosphorylation of glucose indicate that the synthetic peptide described here comprises part of the catalytic site.
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PMID:Glucose phosphorylation. Interaction of a 50-amino acid peptide of yeast hexokinase with trinitrophenyl ATP. 231 95

The atomic models of the complex between rabbit skeletal muscle actin and bovine pancreatic deoxyribonuclease I both in the ATP and ADP forms have been determined by X-ray analysis at an effective resolution of 2.8 A and 3A, respectively. The two structures are very similar. The actin molecule consists of two domains which can be further subdivided into two subdomains. ADP or ATP is located in the cleft between the domains with a calcium ion bound to the beta- or beta- and gamma-phosphates, respectively. The motif of a five-stranded beta sheet consisting of a beta meander and a right handed beta alpha beta unit appears in each domain suggesting that gene duplication might have occurred. These sheets have the same topology as that found in hexokinase.
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PMID:Atomic structure of the actin:DNase I complex. 224 43


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