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)

We have studied glucose phosphorylation at increasing glucose concentrations (1, 5, 10, 25, 50, and 100 mmol/liter) in capillaries of the choroidocapillary lamina from the eye of normal female albino rabbits (n = 10; body wt 1800-2000 g; mean +/- SEM morning glycemia: 147.77 +/- 4.02 mg/dl) and from the eye of spontaneously hyperglycemic rabbits (n = 5, body wt 1800-2000 g, mean +/- SEM morning glycemia; 211.00 +/- 10.76 mg/dl). In the 3000g supernatant of capillary homogenates, the glucose phosphorylating activity (NADP reduction measured as optical density change at 366 nm at pH 7.5) increased progressively with the rise of glucose concentration (r = 0.36; P < 0.05), approaching the peak at high glucose level (25 mmol/liter), with values ranging from 5.32 +/- 0.46 (SEM) nmol/min/mg protein to 7.14 +/- 0.74 (+34.21%, P < 0.01). When measured at a more alkaline pH (8.2) the glucose phosphorylation was higher than at pH 7.5 and retained the responsiveness to increasing glucose concentrations. These kinetic characteristics differ from those seen in most tissues and are somewhat reminiscent of those shown by hepatic glucokinase. Indeed, by subtracting the activity at 1 mmol/liter glucose from that at higher glucose concentrations, we calculated the "glucokinase component" which together with the "hexokinase component" form the total glucose phosphorylating activity. Glucose phosphorylation in capillaries from spontaneously hyperglycemic rabbits was lower than normal (values: 3.66 +/- 0.31 vs 5.32 +/- 0.46 of the normal rabbits; -31.20%; P < 0.05). This could contribute to the hyperglycemia by reducing glucose utilization. However, in these animals the enzyme activity retained the responsivity to increasing glucose concentrations (r = 0.41, P < 0.05). Therefore, the actual capillary glucose phosphorylation in these animals would depend upon both the enzyme level (which is reduced) and the glucose concentration (which is increased). Due to the in vivo inhibition of the hexokinase component, the glucokinase component may be predominant in vivo, making the stimulating effects of hyperglycemia much more pronounced than it would appear from our data in vitro. This may lead to glucose overutilization. These kinetic characteristics of glucose phosphorylation in capillaries might be relevant to the mechanisms leading to diabetic microangiopathy.
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PMID:A glucokinase-like enzyme carries out glucose phosphorylation in capillaries of normal and spontaneously hyperglycemic rabbits. 834 77

A clearer understanding of biochemical properties of oocytes and embryos and their changes in oocyte maturation and embryonic development may have significant clinical implications, especially for in vitro fertilization techniques. Microtechniques and highly sensitive methods such as enzymatic cycling, micro-Western analysis, reverse transcription polymerase chain reaction and so on were employed to study these processes. Low hexokinase activity and high activities of enzymes in the phosphate pathway were characteristic of immature oocytes. During maturation, the activities of hexokinase and phosphofructokinase increased significantly. These changes were used to analyze involvement of epidermal growth factor (EGF) and prostaglandins (PG) in oocyte maturation. EGF is shown to stimulate maturation by increasing PG production in granulosa cells. Electrophysiologically, the sensitivity of oocyte to inositol triphosphate increased and Ca2+ release system developed during maturation. Progesterone production of oocyte and embryos are shown by enzymatic cycling and other methods using radiometry. This hormone produced by embryos themselves may play a role in embryonic development in intracrine fasion. There is 100-fold increase in glucose uptake from oocyte to blastocyst in mice. A switch in substrate preference of the embryo from pyruvate to glucose during preimplantation development may be explained by increases in the activity of hexokinase and expression of glucose transporter, GLUT1. Hexokinase activities determined by NADP cycling increased 20-fold while expression of GLUT1 assessed by micro-Western method 10-fold. GLUT1 expression was also analyzed by RT-PCR, which indicated that the expression is regulated at transcription level. There is a delay in the developmental changes in glucose uptake, hexokinase activity and GLUT1 expression when the embryos are developed in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:[Studies in oocyte maturation and embryonic development]. 837 Oct 11

A nontracer amount of 2-deoxyglucose (DG) was intravenously injected into rats, which were frozen 2 and 4 min later in liquid nitrogen. The freeze-dried samples of cell bodies of anterior horn cells, dorsal root ganglion cells, and cerebellar Purkinje cells, as well as the neuropil adjacent to anterior horn cell bodies, were prepared. Their contents of glucose, glucose 6-phosphate, DG, and 2-deoxyglucose 6-phosphate were microassayed using an enzymatic amplification reaction. NADP cycling. Based on the resulting data and theoretical equations previously described, glucose utilization rate (GUR) and apparent distribution volumes (DVs) of glucose and DG were determined. Anterior horn cell bodies had the highest GUR and their neuropil the lowest, although apparent DVs of glucose and DG were similar in both. This indicates that the glucose supply was equally balanced in all, but that the cell bodies had higher functional activity supported by hexokinase (and other enzymes) related to their energy demands. Dorsal root ganglion cells showed the lowest 2-deoxyglucose 6-phosphate formation rate, but their GUR was slightly higher than that of neuropil because of their markedly large DV of glucose, thus demonstrating that the abundant glucose supply supports the neuronal function. Purkinje cells indicated GUR and apparent DVs similar to molecular and granular layers.
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PMID:Glucose utilization rates in single neurons and neuropil determined by injecting nontracer amounts of 2-deoxyglucose. 843 79

Thirteen kits from different suppliers for measurement of creatine kinase activity in human serum according to the IFCC recommendations were analyzed and compared. Concentrations of AMP, ADP, creatine phosphate, glucose, magnesium ion, NADP+, glucose-6-phosphate dehydrogenase, hexokinase and pH were measured in the reagents by various analytical techniques and compared with those recommended b the IFCC. We also compared by regression analysis the results of creatine kinase catalytic concentration obtained in human sera using commercial kits and in-house prepared reagents according tot he IFCC recommendation. Creatine kinase was also measured in a reference material using the different reagents. The overall results of the activity measurements and the composition of the majority of the kits agree well with one another and with the IFCC recommendation. Minor deviations were found in the evaluation of a few kits. One kit yielded creatine kinase activity values that were 17% lower. Results obtained in the reference material measurements showed differences with some kits which were not found using human sera.
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PMID:Comparison of kits for the determination of creatine kinase activity in serum. 854 39

Two hexokinases were characterized in Schizosaccharomyces pombe: hexokinase 1, with a low phosphorylation coefficient on glucose (Km 8.5 mM) and hexokinase 2, a kinetically conventional hexokinase. Genes hxk1+ and hxk2+ encoding these enzymes were cloned and sequenced. Disruption of hxk1+ had no effect on growth but disruption of hxk2+ doubled the generation time in glucose. Spores carrying the double disruption hxk1+ hxk2+ did not grow on glucose or fructose after one week. Expression of hxk1+ increased strongly during growth in fructose or glycerol. Expression of hxk2+ was highest during growth in glycerol. A NADP-dependent glucose dehydrogenase was detected, but not a glucokinase.
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PMID:Schizosaccharomyces pombe possesses an unusual and a conventional hexokinase: biochemical and molecular characterization of both hexokinases. 854 30

Molecular abnormalities of erythroenzymopathies associated with hereditary hemolytic anemia have been determined by means of molecular biology. Pyruvate kinase (PK) deficiency is the most common and well-characterized enzyme deficiency in the glycolytic pathway, and it causes hereditary hemolytic anemia. To date, 47 gene mutations have been identified. We identified one base deletion, one splicing mutation, and six distinct missense mutations in 12 unrelated families with a homozygous PK deficiency. Mutations located near the substrate or fructose-1,6- diphosphate binding site may change the conformation of the active site, resulting in a drastic loss of activity and severe clinical symptoms. Glucose-6-phosphate dehydrogenase (G6PD)deficiency is the most common metabolic disorder, and it is associated with chronic hemolytic anemia and/or drug- or infection-induced acute hemolytic attack. An estimated 400 million people are affected worldwide. The mutations responsible for about 78 variants have been determined. Some have polymorphic frequencies in different populations. Most variants are produced by one or two nucleotide substitutions. Molecular studies have disclosed that most of the class 1 G6PD variants associated with chronic hemolysis have the mutations surrounding either the substrate or the NADP binding site. Among rare enzymopathies, missense mutations have been determined in deficiencies of glucosephosphate isomerase, (TPI), phosphoglycerate kinase, and adenylate kinase. Compound heterozygosity with missense mutation and base deletion has been determined in deficiencies of hexokinase and diphosphoglyceromutase. Compound heterozygosity with missense and nonsense mutations has been identified in TPI deficiency. One base junction mutations resulting in abnormally spliced PFK-M mRNA have been identified in homozygous PFK deficiency. An exception is hemolytic anemia due to increased adenosine deaminase activity. The basic abnormality appears to result from the overproduction of a structurally normal enzyme.
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PMID:Molecular basis of erythroenzymopathies associated with hereditary hemolytic anemia: tabulation of mutant enzymes. 857 52

In this study changes in alternative pathways of glucose metabolism are examined in the rat lens using radiolabelled glucose in a 1 hr in vitro incubation of 50 mM or 10 mM glucose with or without 0.1 mM phenazine methosulphate (PMS). PMS which reoxidizes NADPH ensures that the pentose phosphate pathway (PPP) is not limited by the supply of NADP+. The data shows that maximal activation of the PPP (with PMS) is 40% greater at high glucose concentrations than normal glucose. This difference in maximal stimulation may be explained by the increase glucose uptake in the hyperglycaemic incubation. In the high-glucose incubation with PMS, hexokinase activity and the glucose 6-phosphate pool is not limiting for the PPP. Under these conditions, PMS alter the NAD+/NADH and NADP+/NADPH ratio. The change in the redox state alters the flux through the polyol pathway, the glycerol 3-phosphate shuttle and the glycolytic control sites, glyceraldehyde 3-phosphate, pyruvate and lactate dehydrogenases. These results are discussed in relation to hyperglycaemia-induced oxidative stress.
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PMID:The effect of phenazine methosulphate on intermediary pathways of glucose metabolism in the lens at different glycaemic levels. 865 4

After having previously shown that some noninsulin-sensitive tissues (capillaries and optic nerve) phosphorylate glucose in a concentration-dependent manner through a glucokinase-like enzyme, here, we report data on glucose phosphorylation in rabbit lens and retina at various glucose concentrations (1, 5, 10, 25, 50, and 100 mmol/L). In the 3000 g supernatant of lens and retina homogenates from two separate groups of female albino rabbits ten animals in each group; 1.8-2.0 kg body weight; mean +/- SEM morning glycemia: 8.19 +/- 0.28 and 8.12 +/- 0.24 mmol/L, respectively) was assayed glucose phosphorylating activity (NADP reduction measured as change in optical density at 366 nm at pH 7.5). The enzyme activity did not reach the maximum at low glucose concentration (1 mmol/L), as it occurs in several tissues, but increased progressively in both tissues with the increase in glucose concentration. Values (mean +/- SEM) for lens were 0.197 +/- 0.031 nmol/min/mg protein at 1 mmol/L and 0.327 +/- 0.051 (the highest value) at 50 mmol/L glucose (+65.99%, p < 0.01; r = 0.31, p < 0.05). Values for retina were 36.02 +/- 2.12 at 1 mmol/L glucose and 42.48 +/- 2.79 (the highest value) at 25 mmol/L glucose (+17.93%, p < 0.001; r = 0.32, p < 0.05). These kinetic characteristics, somewhat reminiscent of those shown by hepatic glucokinase, are still more pronounced when we calculated the "glucokinase component," obtained by subtracting the activity at 1 mmol/L glucose (hexokinase component) from that at the highest glucose concentration (total glucose phosphorylating activity). In five rabbits of similar age and weight, with spontaneous hyperglycemia (mean +/- SEM morning glycemia: 11.71 +/- 0.60) glucose phosphorylation in the retina was lower than normal, value at pH 7.5 and 1 mmol/L glucose being 24.52 +/- 2.20 versus 36.02 +/- 2.12 of normal animals (-31.93%, p < 0.01). This, if occurs also in other tissues, could contribute to the hyperglycemia by reducing glucose utilization. In these animals, however, the glucose phosphorylating activity retained the responsivity to increasing glucose concentrations, with value at 100 mmol/L of 28.65 +/- 2.10, corresponding to + 16.84% over the value at 1 mmol/L (p < 0.01). Therefore, the actual glucose phosphorylation in the retina of these animals would depend both upon the enzyme level (which is reduced) and glucose concentration (which is increased). Due to the in vivo inhibition of the hexokinase component by glucose 6-phosphate, the glucokinase component in retina and lens may be predominant in vivo, making the stimulating effect of hyperglycemia much more important than it would appear from our in vitro data. This might play a role in the chronic diabetic complications.
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PMID:Rabbit lens and retina phosphorylate glucose through a glucokinase-like enzyme: study in normal and spontaneously hyperglycemic animals. 877 33

Oxidative metabolism in the heart is tightly coupled to mechanical work. Because this coupling process is believed to involve Ca2+, the roles of mitochondrial Ca2+ in the regulation of oxidative phosphorylation was studied in isolated rat heart mitochondria. The electrical component of the mitochondrial membrane potential (delta psi) and the redox state of the pyridine nucleotides were determined during the oxidation of various substrates under different metabolic states. In the absence of added adenine nucleotides, the NADP+ redox couple was almost completely reduced, regardless of the specific substrate and the presence of Ca2+, whereas NAD+ couple redox state was highly dependent on the substrate type and the presence of Ca2+. Titration of respiration with ADP, in the presence of excess hexokinase and glucose, showed that both respiration and NAD(P)+ reduction were very sensitive to ADP. The maximal enzyme reaction rate of ADP-stimulated respiration Michaelis constants (Km) for ADP were dependent on the particular substrate employed. delta psi was much less sensitive to ADP. With either alpha-ketoglutarate or glutamate as substrate, Ca2+ significantly increased reduction of NAD(P)+.Ca2+ did not influence NAD(P)+ reduction with either acetylcarnitine or pyruvate as substrate. In the presence of ADP, delta psi was increased by Ca2+ at all metabolic states with glutamate plus malate, 0.5 mM alpha-ketoglutarate plus malate, or pyruvate plus malate as substrates. The data presented support the hypothesis that cardiac respiration is controlled by the availability of both Ca2+ and ADP to mitochondria. The data indicate that an increase in substrate supply to mitochondria can increase mitochondrial respiration at given level of ADP. This effect can be produced by Ca2+ with substrates such as glutamate, which utilize alpha-ketoglutarate dehydrogenase activity for oxidation. Increases in respiration by Ca2+ may mitigate an increase in ADP during periods of increased cardiac work.
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PMID:Substrate specific effects of calcium on metabolism of rat heart mitochondria. 896 82

Hexokinase and D-glucose-6-phosphate dehydrogenase (G6PDH) from Schizosaccharomyces pmbe have been purified 250-fold by an identical three-step. Both enzymes are dimeric with a molecular mass of 88 kDa for the kinase and 112 kDa for the dehydrogenase. Steady-state kinetic studies were performed on hexokinase and G6PDH, which form the glucose phosphate branch of the oxidative pentose phosphate pathway of S. pombe (fission yeast). Hexokinase promotes Mg(2+)-activated phosphorylation of D-glucose by the equilibrium random Bi Bi mechanism with formation of the abortive enzyme-ADP-glucose complex. ADP inhibits the kinase competitively versus ATP and noncompetitively versus D-glucose. The Mg2+ activation of hexokinase is associated with an increase in the maximal velocity by its interaction with the ternary complex to facilitate the transfer of the phosphoryl group. G6PDH catalyzes NADP(+)-linked oxidation of D-glucose-6-phosphate by the ordered Bi Bi mechanism with NADP+ as the leading reactant. High NADP+ concentration inhibits the dehydrogenase by forming the dead-end ternary complex. In addition, G6PDH is also subjected to product inhibition by NADPH and noncompetitive inhibition by A(G)TP. Thus, the oxidative pentose phosphate pathway in S. pombe may be regulated via inhibition of hexokinase by ADP in conjunction with inhibition of G6PDH by NADPH and ATP.
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PMID:Purification and kinetic characterization of hexokinase and glucose-6-phosphate dehydrogenase from Schizosaccharomyces pombe. 966 12


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