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)

Yeast mutants blocked at different steps of the glycolytic pathways have been used to study the inactivation of several gluconeogenic enzymes upon addition of sugars. While phosphorylation of the sugars appears a requisite for the inactivation of fructose 1,6-bisphosphatase and phosphoenol-pyruvate carboxykinase, malate dehydrogenase is inactivated by fructose in mutants lacking hexokinase. The normal inactivation elicited by glucose in a mutant lacking phosphofructokinase indicates that the process does not require metabolism of the sugar beyond hexose monophosphates. A possible role for ATP in the inactivation process is suggested.
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PMID:Inactivation of gluconeogenic enzymes in glycolytic mutants of Saccharomyces cerevisiae. 23 32

The hepatocyte and haematopoietic cell contents of the liver of the foetal guinea pig were measured over the latter half of gestation. Hepatocytes represented about 30% of liver volume at mid-gestation and this increased to 70-80% by term; cell volume remained fairly constant until 5-7 days before term, then more than doubled. Haematopoietic cells represented about 5% of liver volume at mid-gestation and this progressively fell to <1% by term. At 75% of gestation hepatocytes and haematopoietic cells were prepared from perfused foetal livers by collagenase digestion. Enzyme activity of the hepatocyte was, without exception, similar to that of the whole liver. In general, enzyme activity in the haematopoietic cells was similar to that in erythrocytes, with relatively low values for aldolase, glycerol 3-phosphate dehydrogenase, phosphoglycerate mutase, enolase, lactate dehydrogenase, phosphoenolpyruvate carboxykinase, fructose 1,6-bisphosphatase, isocitrate dehydrogenase, ;malic' enzyme, glutamate dehydrogenase and aspartate aminotransferase. The haematopoietic cell contribution to total enzyme activity in the foetal liver was usually much less than 10% and could thus not account for the major changes in hepatic enzyme activity over the latter half of gestation. Hepatocytes contained hexokinase isoenzymes I and III, aldolase isoenzymes A and B and pyruvate kinase isoenzymes 1, 2 and 4. The haematopoietic cells contained hexokinase isoenzyme I and two additional bands of activity with slightly greater mobility, aldolase isoenzyme A and pyruvate kinase isoenzymes 2 and 4.
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PMID:The distribution of enzyme and isoenzyme activities between parenchymal and haematopoietic cells in the liver of the foetal guinea pig. 43 88

Optimal concentrations of the essential components for analyzing the activity of each enzyme associated with glycolysis and gluconeogenesis in rabbit periodontal ligament were examined, and enzyme assay systems for 15 enzymes including 22 reactions were established using triethanolamine buffer. Specific activities of all the enzymes, except for the gluconeogenic reaction of phosphoglycerate kinase, were systematically evaluated using the optimum buffer for each enzyme, since the activity of each enzyme varied depending on the buffer used. For glycolysis, the activity levels of hexokinase and 6-phosphofructokinase were very low, and consequently these enzyme reactions were inferred to be the rate-limiting steps. For gluconeogenesis, fructose 1,6-bisphosphatase and aldolase activities were extremely low, and the activities of glucose 6-phosphatase, phosphoenolpyruvate carboxykinase and pyruvate carboxylase were undetectable. These results suggest that the periodontal ligament may have no gluconeogenesis capability. With a rise in pH, the activities of the key enzymes of glycolysis gradually increased, and a specific "crossover" point was found between the activities of glyceraldehyde-phosphate dehydrogenase and phosphoglyceromutase. In addition, the activity of fructose 1,6-bisphosphatase, one of the key enzymes of gluconeogenesis, was markedly increased with a rise in pH, although pH changes had no effect on aldolase activity. Consequently, alkaline pH appeared to result in overall stimulation of glycolysis.
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PMID:Enzymatic regulation of glycolysis and gluconeogenesis in rabbit periodontal ligament under various physiological pH conditions. 165 53

An indirect immunoperoxidase procedure has been used to demonstrate sites of glycolysis and gluconeogenesis in normal rat kidney and liver. In kidney, the gluconeogenic enzyme fructose 1,6-biphosphatase was restricted to the proximal tubular epithelium, while the glycolytic enzyme hexokinase predominated in more distal segments. Intense staining for the biphosphatase in proximal convoluted tubular brush borders suggests that reabsorbed substrates may be used directly at this site in renal gluconeogenesis. In view of the high phosphofructokinase and pyruvate kinase activities present in collecting ducts, their relatively low hexokinase activities and their relatively pale immunostaining for hexokinase indicate that glycolytic substrates which feed into the pathway subsequent to the initial phosphorylation step, rather than glucose, may be the major energy source for the rat renal papilla. Immunostaining in the liver was consistent with the metabolic zonation of liver parenchyma, in that glucokinase occurred mainly in perivenous regions and fructose 1,6-bisphosphatase in periportal areas. The presence of such metabolic zonation is difficult to reconcile with the widely held view that the majority of hepatic glycogen is derived directly from glucose. A model for hepatic glycogen synthesis is proposed which links the concept of parenchymal zonal heterogeneity with recent biochemical evidence concerning the 'glucose paradox' and with microscopical studies on the dynamics of glycogen deposition after refeeding.
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PMID:The compartmentation of glycolytic and gluconeogenic enzymes in rat kidney and liver and its significance to renal and hepatic metabolism. 242 78

Glucokinase, hexokinase, fructose 1,6-bisphosphatase and phosphoenolpyruvate carboxykinase specific activities were monitored in liver cytosol from rats that had been made cancerous with 1,2-dimethylhydrazine and then treated with hydrazine sulfate. The presence of intestinal cancer, specifically, was confirmed by laparotomy and by histological analysis. Sustained changes in hexokinase and glucokinase specific activities were first evident during the latter weeks that the carcinogen was being administered. Upon subsequent treatment with hydrazine sulfate, glucokinase activity further decreased, and liver cytosolic phosphoenolpyruvate carboxykinase activity increased. Liver cytosolic hexokinase and fructose 1,6-bisphosphatase specific activities were not appreciably affected by the hydrazine sulfate treatment. These results indicate that hydrazine sulfate may influence carbohydrate metabolism at the level of selected liver enzymes not only with respect to gluconeogenesis, but also in terms of glucose uptake.
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PMID:Effect of hydrazine sulfate on glucose-regulating enzymes in the normal and cancerous rat. 270 33

Activities of key carbohydrate-metabolizing enzymes in biopsied human tissues of hepatocellular carcinoma and related conditions were determined by established methods. Among the enzymes analyzed, fetal-type liver enzymes (low-Km hexokinase, glucose 6-phosphate dehydrogenase, and pyruvate kinase-M2) showed increased activities, and adult-type liver enzymes [glucose 6-phosphatase, fructose 1,6-bisphosphatase, high-Km hexokinase (or glucokinase), and pyruvate kinase-L] showed decreased activities, resulting in undifferentiated enzyme patterns not only in fetal livers and hepatocellular carcinomas but also in livers of acute and chronic hepatitis and liver cirrhosis with or without tumors. Hepatocellular carcinomas showed a general tendency of having greater enzyme deviations than hepatitic and cirrhotic livers. The extent of the enzyme deviation in hepatocellular carcinomas varied considerably from one enzyme to another for each tumor tissue as compared with that in the benign liver diseases. Thus, the phenotypic heterogeneity was important for discriminating between the neoplastic and inflammatory changes in differentiation markers. The enzyme patterns of tumors and their corresponding host cirrhotic livers were unrelated, suggesting that the cirrhotic liver has a significance as preneoplastic state only in terms of having a high incidence of evolving hepatocellular carcinoma.
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PMID:Profiles of carbohydrate-metabolizing enzymes in human hepatocellular carcinomas and preneoplastic livers. 282 76

The activity of some enzymes in a given metabolic pathway is modulated through multiple mechanisms, which operate in a simultaneous and coherent way to produce either stimulation or inhibition. The operation of these mechanisms is illustrated with several enzymes involved in glucose metabolism, by choosing examples from the presentations at the Symposium. Thus the reciprocal interactions of the regulatory mechanisms acting upon hexokinase D ('glucokinase'), phosphofructokinase, fructose 1,6-bisphosphatase and pyruvate kinase were discussed, as well as their relationships with the induction of enzyme conformational changes. In addition, the effects of covalent interconversions on glutamine synthetase activity were briefly analyzed. An outstanding feature exhibited by all these enzymes is the display of a great number of elasticity coefficients, which are differential quotients measuring the dependence of enzymatic activity on each variable that modulates it. A general assumption is that these enzymes make an important contribution to the control of the metabolic flux in which they participate. The flux control, however, appears to be shared in different degrees by all the components of the system, and may be quantified through the differential quotient denominated control coefficient. Some of the problems that emerge in any attempt to estimate these coefficients in the living cells are discussed. The problems derive partly from the complex subcellular structure, the formation of functional compartments resulting from reversible association of the enzymes, one to another and to different cellular components, and the actual state of cell water. These problems make that the results obtained with purified and highly diluted enzymes in most enzymological studies should not be extrapolated directly to what happens in vivo, without a careful evaluation of each particular case. The regulatory role of enzyme activity of fructose 2,6-bisphosphate and its eventual participation as an intermediary in the hormonal control of glycolytic and gluconeogenic fluxes are emphasized. The regulation of yeast fructose 1,6-bisphosphate activity is discussed in relation to the eventual role of allosteric modulators and covalents interconversions as signals for the initiation of intracellular degradation of the enzyme during catabolic inactivation.
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PMID:[Concurrence of multiple and integrated mechanisms in the modulation of enzyme activities: significance for the regulation of metabolic fluxes]. 301 48

We studied the effects of insulin and glucagon on energy and carbohydrate metabolism of rat hepatocytes in primary culture. The aim of this study is to elucidate the mechanism of the synergistic action of insulin and glucagon and to evaluate the combined effects of these hormones on liver injury. Insulin increased the level of adenosine triphosphate in hepatocytes in the presence of glucagon. Insulin increased the activities of glucokinase (EC 2.7.1.1), phosphofructokinase (EC 2.7.1.11), pyruvate kinase (EC 2.7.1.40) type L and glucose 6-phosphate dehydrogenase (EC 1.1.1.49). Glucagon had no antagonistic effect on these increases. Glucagon increased the activity of glucose 6-phosphate (EC 3.1.3.9) (G6Pase) in the presence or absence of insulin, while insulin had no effects on the levels of G6Pase and fructose 1,6-bisphosphatase (EC 3.1.3.11) in the presence or absence of glucagon. Metabolite analysis of cultured hepatocytes indicated that insulin and glucagon have antagonistic effects on the glycolytic activity of hepatocytes. These combined effects of insulin and glucagon may partially explain the preventive effects of these hormones on liver injury.
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PMID:Effects of insulin and glucagon on energy and carbohydrate metabolism of rat hepatocytes in primary culture. 306 23

Glucagon and dibutyryl cyclic AMP inhibited glucose utilization and lowered fructose 2,6-bisphosphate levels of hepatocytes prepared from fed chickens. Partially purified preparations of chicken liver 6-phosphofructo-1-kinase and fructose 1,6-bisphosphatase were activated and inhibited by fructose 2,6-bisphosphate, respectively. The sensitivities of these enzymes and the changes observed in fructose 2,6-bisphosphate levels are consistent with an important role for this allosteric effector in hormonal regulation of carbohydrate metabolism in chicken liver. In contrast, oleate inhibition of glucose utilization by chicken hepatocytes occurred without change in fructose, 2,6-bisphosphate levels. Likewise, pyruvate inhibition of lactate gluconeogenesis in chicken hepatocytes cannot be explained by changes in fructose 2,6-bisphosphate levels. Exogenous glucose caused a marked increase in fructose 2,6-bisphosphate content of hepatocytes from fasted but not fed birds. Both glucagon and lactate prevented this glucose effect. Fasted chicken hepatocytes responded to lower glucose concentrations than fasted rat hepatocytes, perhaps reflecting the species difference in hexokinase isozymes.
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PMID:Role of fructose 2,6-bisphosphate in the regulation of glycolysis and gluconeogenesis in chicken liver. 631 91

2,5-Anhydro-D-mannitol (100 to 200 mg/kg) decreased blood glucose by 17 to 58% in fasting mice, rats, streptozotocin-diabetic mice, and genetically diabetic db/db mice. Serum lactate in rats was elevated 56% by 2,5-anhydro-D-mannitol, but this could be prevented by dichloroacetate (200 mg/kg) or thiamin (200 mg/kg). In hepatocytes from fasted rats, 1 mM 2,5-anhydro-D-mannitol inhibited gluconeogenesis from a mixture of alanine, lactate, and pyruvate. It also inhibited glucose production and stimulated lactate formation from glycerol or dihydroxyacetone. Glycogenolysis in hepatocytes from fed rats was markedly inhibited by 1 mM 2,5-anhydro-D-mannitol both in the presence or absence of 1 microM glucagon. 2,5-Anhydro-D-mannitol can be phosphorylated by fructokinase or hexokinase to the 1-phosphate and then by phosphofructokinase to the 1,6-bisphosphate. Rat liver glycogen phosphorylase was inhibited by 2,5-anhydro-D-mannitol 1-phosphate (apparent Ki = 0.66 +/- 0.09 mM) but was little affected by 2,5-anhydro-D-mannitol 1,6-bisphosphate. Rat liver phosphoglucomutase was inhibited by 2,5-anhydro-D-mannitol 1-phosphate (apparent Ki = 2.8 +/- 0.2 mM), whereas 2,5-anhydro-D-mannitol 1,6-bisphosphate served as an alternative activator (apparent K alpha = 7.0 +/- 0.5 microM). Rabbit liver pyruvate kinase was activated by 2,5-anhydro-D-mannitol 1,6-bisphosphate (apparent K alpha = 9.5 +/- 0.9 microM), whereas rabbit liver fructose 1,6-bisphosphatase was inhibited by 2,5-anhydro-D-mannitol 1,6-bisphosphate (apparent Ki = 3.6 +/- 0.3 microM). The phosphate esters of 2,5-anhydro-D-mannitol would, therefore, be expected to inhibit glycogenolysis and gluconeogenesis and stimulate glycolysis in liver.
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PMID:Inhibition of gluconeogenesis and glycogenolysis by 2,5-anhydro-D-mannitol. 642 25


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