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)

In the absence of fructose 6-phosphate, the regulatory protein of rat liver glucokinase (hexokinase IV or D) inhibited this enzyme, though with a much (15-fold) lower potency than in the presence of a saturating concentration of fructose 6-phosphate. Evidence is provided that this inhibition is not due to contaminating fructose 6-phosphate. In the presence of regulatory protein, sorbitol 6-phosphate, a potent analog of fructose 6-phosphate, exerted a hyperbolic, partial inhibition on glucokinase, the degree of which increased with the concentration of regulatory protein. Plots of the reciprocal of the difference between the rates in the absence and in the presence of sorbitol 6-phosphate versus 1/[sorbitol 6-phosphate] at various concentrations of regulatory protein were linear, and demonstrated that the apparent affinity for sorbitol 6-phosphate increased with the concentration of regulatory protein. Plots of the reciprocal of the difference between 1/v in the presence and in the absence of sorbitol 6-phosphate versus 1/[sorbitol 6-phosphate] were also linear and crossed the axis at a value independent of the concentration of regulatory protein. Fructose 1-phosphate released the inhibition exerted by the regulatory protein in a hyperbolic fashion. The concentration of this effector required for a half-maximal effect increased linearly with the concentrations of sorbitol 6-phosphate and of regulatory protein. These results are consistent with a model in which the regulatory protein exists under two conformations, one form which binds inhibitors and glucokinase, and the other which binds activators, although not glucokinase. Sorbitol 6-phosphate, 2-deoxysorbitol 6-phosphate and mannitol 1-phosphate, all analogs of the open-chain configuration of fructose 6-phosphate, inhibited glucokinase in the presence of regulatory protein at lower concentrations than fructose 6-phosphate, whereas fixed analogs of the furanose form of fructose 6-phosphate were inactive or behaved as activators. This indicated that fructose 6-phosphate in its open-chain configuration is recognized by the regulatory protein. A series of compounds exerted an activating effect. These included, in order of decreasing potency: fructose 1-phosphate, psicose 1-phosphate, ribitol 5-phosphate, analogs of fructose 1-phosphate and of ribitol 5-phosphate and, at much higher concentrations, inorganic phosphate.
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PMID:Effectors of the regulatory protein acting on liver glucokinase: a kinetic investigation. 188 18

The enzyme activities involved in fructose metabolism were measured in samples of human liver. On the basis of U/g of wet-weight the following results were found: ketohexokinase, 1.23; aldolase (substrate, fructose-1-phosphate), 2.08; aldolase (substrate, fructose-1,6-diphosphate), 3.46; triokinase, 2.07; aldehyde dehydrogenase (substrate, D-glyceraldehyde), 1.04; D-glycerate kinase, 0.13; alcohol dehydrogenase (nicotinamide adenine dinucleotide [NAD]) substrate, D-glyceraldehyde), 3.1; alcohol dehydrogenase (nicotinamide adenine dinucleotide phosphate [NADP]) (substrate, D-glyceraldehyde), 3.6; and glycerol kinase, 0.62. Sorbitol dehydrogenases (25.0 U/g), hexosediphosphatase (4.06 U/g), hexokinase (0.23 U/g), and glucokinase (0.08 U/g) were also measured. Comparing these results with those of the rat liver it becomes clear that the activities of alcohol dehydrogenases (NAD and NADP) in rat liver are higher than those in human liver, and that the values of ketohexokinase, sorbitol dehydrogenases, and hexosediphosphatase in human liver are lower than those values found in rat liver. Human liver contains only traces of glycerate kinase. The rate of fructose uptake from the blood, as described by other investigators, can be based on the activity of ketohexokinase reported in the present paper. In human liver, ketohexokinase is present in a four-fold activity of glucokinase and hexokinase. This result may explain the well-known fact that fructose is metabolized faster than glucose.
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PMID:Enzymes of fructose metabolism in human liver. 438 49

In peach trees (Prunus persica L. Batsch cv. Redhaven), sorbitol is a primary photosynthetic product and may play an important role in the budbreak process. Surprisingly, before budbreak (from January to early March), the concentration of sorbitol in the xylem sap decreases, while that of hexoses (glucose and fructose) increases. The aim of this work was to study the control of sorbitol uptake into vegetative buds by hexoses. Sorbitol uptake was selectively inhibited by hexoses at low and physiological concentrations and this effect was both reversible and concentration-dependent. In addition, the active uptake of sorbitol significantly declined in the plasma membrane vesicles-enriched fraction purified from glucose-treated vegetative buds, suggesting that the inhibitory action of glucose was at the membrane level. Finally, among several glucose analogues tested, only hexokinase substrates (2-deoxyglucose and mannose) were able to mimic the glucose effect, which was completely blocked by the hexokinase inhibitor mannoheptulose. These results represent the first steps towards a better understanding of polyol transport control in plants.
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PMID:Sorbitol uptake is regulated by glucose through the hexokinase pathway in vegetative peach-tree buds. 1499 Jun 20

Sorbitol and sucrose are major products of photosynthesis distributed in apple trees (Malus domestica Borkh. cv. "Greensleeves") that affect quality in fruit. Transgenic apple plants were silenced or up-regulated for sorbitol-6-phosphate dehydrogenase by using the CaMV35S promoter to define the role of sorbitol distribution in fruit development. Transgenic plants with suppressed sorbitol-6-phosphate dehydrogenase compensated by accumulating sucrose and starch in leaves, and morning and midday net carbon assimilation rates were significantly lower. The sorbitol to sucrose ratio in leaves was reduced by approximately 90% and in phloem exudates by approximately 75%. The fruit accumulated more glucose and less fructose, starch, and malic acid, with no overall differences in weight and firmness. Sorbitol dehydrogenase activity was reduced in silenced fruit, but activities of neutral invertase, vacuolar invertase, cell wall-bound invertase, fructose kinase, and hexokinase were unaffected. Analyses of transcript levels and activity of enzymes involved in carbohydrate metabolism throughout fruit development revealed significant differences in pathways related to sorbitol transport and breakdown. Together, these results suggest that sorbitol distribution plays a key role in fruit carbon metabolism and affects quality attributes such as sugar-acid balance and starch accumulation.
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PMID:Silencing leaf sorbitol synthesis alters long-distance partitioning and apple fruit quality. 1713 42