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)

Three functions have been suggested to be localized in contact sites between the inner and the outer membrane of mitochondria from mammalian cells: (i) transfer of energy from matrix to cytosol through the action of peripheral kinases; (ii) import of mitochondrial precursor proteins; and (iii) transfer of lipids between outer and inner membrane. In the contact site-related energy transfer a number of kinases localized in the periphery of the mitochondrion play a crucial role. Two examples of such kinases are relevant here: (i) hexokinase isoenzyme I which is capable of binding to the outer aspect of the outer membrane; and (ii) the mitochondrial isoenzyme of creatine kinase which is localized in the intermembrane space. Recently, evidence was presented that both hexokinase and creatine kinase are preferentially localized in contact sites (Adams, V. et al. (1989) Biochim. Biophys. Acta 981, 213-225). The aim of the present experiments was two-fold. First, to establish methods which enable the bioenergetic aspects of energy transfer mediated by kinases in contact sites to be measured. In these experiments emphasis was on hexokinase, while 31P-NMR was the major experimental technique. Second, we wanted to develop methods which can give insight into factors playing a role in the formation of contact sites involved in energy transfer. In the latter approach, mitochondrial creatine kinase was studied using monolayer techniques.
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PMID:The role of contact sites between inner and outer mitochondrial membrane in energy transfer. 220 72

Nine bodybuilders performed heavy-resistance exercise activating the quadriceps femoris muscle. Intermittent 30-s exhaustive exercise bouts comprising 6-12 repetitions were interspersed with 60-s periods for 30 min. Venous blood samples were taken repeatedly during and after exercise for analyses of plasma free fatty acid (FFA) and glycerol concentration. Muscle biopsies were obtained from the vastus lateralis muscle before and after exercise and assayed for glycogen, glycerol-3-phosphate, lactate and triglyceride (TG) content. The activities of citrate synthase (CS), lactate dehydrogenase, hexokinase (HK), myokinase, creatine kinase and 3-hydroxyacyl-CoA dehydrogenase (HAD), were analysed. Histochemical staining procedures were used to assess fibre type composition, fibre area and capillary density. TG content before and after exercise averaged (SD) 23.9 (13.3) and 16.7 (6.4) mmol kg-1 dry wt. The basal triglyceride content varied sixfold among individuals and the higher the levels the greater was the change during exercise. The glycogen content decreased (P less than 0.001) from 690 (82) to 495 (95) mmol kg-1 dry wt. and lactate and glycerol-3-phosphate increased (P less than 0.001) to 79.5 (5.5) and 14.5 (7.3) mmol kg-1 dry wt., respectively, after exercise. The HK and HAD/CS content respectively correlated with glycogen or TG content at rest and with changes in these metabolites during exercise. FFA and glycerol concentrations increased slightly (P less than 0.001) during exercise. Lipolysis may, therefore, provide energy during heavy-resistance exercise of relatively short duration. Also, storage and utilization of intramuscular substrates appear to be influenced by the metabolic profile of muscle.
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PMID:Glycogen and triglyceride utilization in relation to muscle metabolic characteristics in men performing heavy-resistance exercise. 228 98

The location of hexokinase at the surface of brain mitochondria was investigated by electron microscopy using immuno-gold labelling techniques. The enzyme was located where the two mitochondrial limiting membranes were opposed and contact sites were possible. Disruption of the outer membrane by digitonin did not remove bound hexokinase and creatine kinase from brain mitochondria, although the activity of outer membrane markers and adenylate kinase decreased, suggesting a preferential location of both enzymes in the contact sites. In agreement with that, a membrane fraction was isolated from osmotically lysed rat brain mitochondria in which hexokinase and creatine kinase were concentrated. The density of this kinase-rich fraction was specifically increased by immuno-gold labelling of hexokinase, allowing a further purification by density gradient centrifugation. The fraction was composed of inner and outer limiting membrane components as shown by the specific marker enzymes, succinate dehydrogenase and NADH-cytochrome-c-oxidase (rotenone insensitive). As reported earlier for the enriched contact site fraction of liver mitochondria the fraction from brain mitochondria contained a high activity of glutathione transferase and a low cholesterol concentration. Moreover, the contacts showed a higher Ca2+ binding capacity in comparison to outer and inner membrane fractions. This finding may have regulatory implications because glucose phosphorylation via hexokinase activated the active Ca2+ uptake system and inhibited the passive efflux, resulting in an increase of intramitochondrial Ca2+.
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PMID:Mitochondrial boundary membrane contact sites in brain: points of hexokinase and creatine kinase location, and control of Ca2+ transport. 245 93

A membrane fraction of intermediate density between inner and outer membrane was isolated by density gradient centrifugation from osmotically disrupted mitochondria of rat liver, brain, and kidney. The fraction was hexokinase rich and could therefore be further purified using specific antibodies against hexokinase and immunogold labelling techniques. In agreement with recent findings the gradient fraction which cosedimented with hexokinase contained the boundary membrane contact sites because it was composed of outer and inner membrane components and beside hexokinase, was enriched also by activity of creatine kinase and nucleoside diphosphate kinase. In contrast the activity of adenylate kinase appeared to be concentrated beyond the contact sites in the outer membrane fraction. By employing surface proteolysis analysis and specific blockers of the outer membrane pore we observed that the location of the kinases relative to the membrane components in the contact fraction resembled that of intact mitochondria. This specific organization of some peripheral kinases in the contact sites suggested an important role of the voltage dependence of the outer membrane pore, in that the pore may become limiting in anion exchange because of influence of the inner membrane potential on the closely attached outer membrane. Such control of anion exchange would lead to a dynamic compartmentation at the mitochondrial surface by the formation of contact sites, which may explain the preferential utilization of cytosolic creatine by the mitochondrial creatine kinase, as postulated in the phosphocreatine shuttle.
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PMID:Further characterization of contact sites from mitochondria of different tissues: topology of peripheral kinases. 254 59

The skeletal muscle has the capacity to respond adaptively to increased use. This observation could open up the feasibility of constructing pumping chambers to support or even replace cardiac work. We investigated the changes in enzyme activity due to chronic stimulation in an animal skeletal muscle. In 5 adult sheep the psoas muscle of one side was electrically stimulated through the muscle nerves, with an implantable stimulation unit for 5 weeks. The activity of the hexokinase (E.C.2.7.1.1.), lactate dehydrogenase (E.C.1.1.1.27), malate dehydrogenase (E.C.1.1.1.37), creatine kinase (E.C.2.7.3.2.) choline acetyltransferase and the contents of adenosine triphosphate and adenosine diphosphate were determined in bioptic specimen. The use of only 15 Hertz as a stimulation frequency led to a transformation of an originally fast-twitch muscle into a slow-twitch muscle with reduced susceptibility to fatigue. These results indicate a potential role of the skeletal muscle as an ideal myocardial substitute with the ability to perform hemodynamic work.
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PMID:[Biochemical changes in skeletal muscles after chronic indirect stimulation]. 260 58

An assay system for creatine kinase using microtiter plates and a plate reader that records absorbancies at 405 nM has been devised. The system is an adaptation of well-established assays that couple creatine kinase with the reactions catalyzed by hexokinase and glucose-6-phosphate dehydrogenase (G6PDH), to give a measurable increase in reduced pyridine nucleotide quantitated by absorbance at 340 nM. Two features of this system are modified for reading at 405 nM: (i) The thioamido derivative of NAD is used because its reduced form exhibits a substantial increase in absorbance at 405 nM, the most commonly available wavelength on microplate readers; and (ii) glucose-6-phosphate dehydrogenase from Leuconostoc mesenteroides is used because it can reduce either NAD or NADP (unlike most other G6PDH enzymes, which require NADP), thus making it unnecessary to use the more expensive thio-NADP. The rate of thio-NAD reduction is linear with enzyme concentration and time over a 20-fold range of concentrations of purified creatine kinase, and the assay also works well with myogenic cells allowed to grow and differentiate in the 96-well plate in which the assay is performed. This system offers considerable savings in cells, time, and material in studies of muscle cell differentiation, for which creatine kinase levels are frequently measured. It also provides a potential method for the convenient and economical measurement of activities of many other enzymes that can be coupled to reduction of thio-NAD.
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PMID:Assay of creatine kinase in microtiter plates using thio-NAD to allow monitoring at 405 nM. 261 Mar 56

We show in the accompanying paper that the steady-state level of free Ca2+ maintained by the organelles of permeabilized RINm5F insulinoma cells varies inversely with the ATP/ADP ratio when this ratio is set by addition of creatine phosphokinase and fixed ratios of creatine to creatine phosphate. We, therefore, asked whether acute cyclic alterations in the cytosolic ATP/ADP ratio in the range known to modulate O2 consumption might be involved in regulating the physiological activity of Ca2+ -ATPases and the cytosolic free Ca2+ level. To explore this hypothesis we combined two experimental systems: 1) permeabilized RINm5F insulinoma cells that can maintain a low medium Ca2+ concentration and 2) a cell-free extract of rat skeletal muscle that spontaneously exhibits oscillatory behavior of glycolysis and linked oscillations in the ATP/ADP ratio, when provided with glucose. The free Ca2+ level maintained by the permeabilized cells oscillated in phase with the glycolytic oscillations and correlated closely with the ATP/ADP ratio but not with glucose 6-phosphate, fructose 6-phosphate, orthophosphate, or pH. When glucokinase replaced hexokinase as the glucose phosphorylating enzyme, Ca2+ oscillations were induced by increasing the glucose concentration from 2 to 8 mM. The results demonstrate a link between metabolite changes and free Ca2+ levels in a reconstituted physiological system. They support a model in which oscillations in glycolysis and the ATP/ADP ratio may cause oscillations in cytosolic free Ca2+, beta-cell electrical activity, and insulin release.
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PMID:Linked oscillations of free Ca2+ and the ATP/ADP ratio in permeabilized RINm5F insulinoma cells supplemented with a glycolyzing cell-free muscle extract. 283 Dec 25

Under effects of myocardial ischemia (30 min), the activities of the intermembrane enzymes of rabbit heart mitochondria, i.e., adenylate kinase and creatine kinase, are inhibited by 20% and 23%, respectively. Consequently, the creatine- and AMP-activated respiration of mitochondria diminishes by 52% and 39%, respectively. An inhibitory analysis of ADP-, AMP- and creatine-activated mitochondrial respiration performed in the presence of atractyloside has demonstrated that ischemia (30 min), adriblastin (0.688 mM) and succinate (10 mM) cause alterations in the functional coupling of adenylate kinase and creatine kinase with the adenine nucleotide translocator. These alterations lead to the diminution of the rate and efficiency of energy transfer from mitochondria to hexokinase, as an arbitrary site of energy consumption. An addition of cytochrome c to ischemic heart mitochondria results in an increase in the rate of ATP synthesis; however, the efficiency of this process is lowered. The toxic effect of the anticancer drug--adriblastin on heart mitochondria respiration is enhanced in the presence of creatine in the bathing solution.
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PMID:[Functional changes in the mitochondrial site of adenylate kinase and creatine kinase systems of energy transport induced by myocardial ischemia and adriablastin]. 284 Jan 29

The purpose of the study was to estimate the genetic effect for skeletal muscle characteristics using pairs of nontwin brothers (n = 32), dizygotic (DZ) twins (n = 26), and monozygotic (MZ) twins (n = 35). They were submitted to a needle biopsy of the vastus lateralis for the determination of fiber type distribution (I, IIa, IIb) and the following enzymes were assayed for maximal activity: creatine kinase, hexokinase, phosphofructokinase (PFK), lactate dehydrogenase, malate dehydrogenase, 3-hydroxyacyl CoA dehydrogenase, and oxoglutarate dehydrogenase (OGDH). For the percentage of type I fibers, intraclass correlations were 0.33 (p less than 0.05), 0.52 (p less than 0.01), and 0.55 (p less than 0.01) in brothers and DZ and MZ twins, respectively. MZ twins exhibited significant within-pair resemblance for all enzyme activities (0.30 less than or equal to r less than or equal to 0.68). In spite of these correlations, genetic analyses performed with the twin data alone indicated that there was no significant genetic effect for muscle fiber type I, IIa, and IIb distribution and fiber areas. Although there were significant correlations in MZ twins for all muscle enzyme activities, the often nonsignificant intraclass coefficients found in brothers and DZ twins suggest that variations in enzyme activities are highly related to common environmental conditions and nongenetic factors. However, genetic factors appear to be involved in the variation of regulatory enzymes of the glycolytic (PFK) and citric acid cycle (OGDH) pathways and in the variation of the oxidative to glycolytic activity ratio (PFK/OGDH ratio). Data show that these genetic effects reach only about 25-50% of the total phenotypic variation when data are adjusted for age and sex differences.
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PMID:Genetic effects in human skeletal muscle fiber type distribution and enzyme activities. 294 86

Twenty-three male Black African and 23 male Caucasian subjects, ascertained as sedentary, participated in this study designed to determine whether there were differences in skeletal muscle histochemical and biochemical characteristics between racial groups. Muscle fiber type proportions (I, IIa, and IIb), fiber areas and activities of several enzyme markers of different energy metabolic pathways were determined from a biopsy of the vastus lateralis. Results indicated that Caucasians had a higher percent type I (8%, P less than 0.01) and a lower percent type IIa (6.7%, P less than 0.05) fiber proportions than Africans. No significant differences were observed between the two racial groups in the type IIb fiber proportion or in the three fiber type areas. Enzymes catalyzing reactions in phosphagenic [creatine kinase (CK)] and glycolytic [hexokinase (HK), phosphofructokinase (PFK), and lactate dehydrogenase (LDH)] metabolic pathways had significantly higher activities (about 30-40%) in the Black African group than in the Caucasian group (P less than 0.01). No significant difference was noted in the activities of oxidative enzymes [malate dehydrogenase (MDH), oxoglutarate dehydrogenase (OGDH), and 3-hydroxyacyl-CoA dehydrogenase (HADH)]. Consequently, the PFK/OGDH ratio was significantly elevated in Africans (P less than 0.05). The racial differences observed between Africans and Caucasians in fiber type proportion and enzyme activities of the phosphagenic and glycolytic metabolic pathways may well result from inherited variation. These data suggest that sedentary male Black individuals are, in terms of skeletal muscle characteristics, well endowed for sport events of short duration.
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PMID:Skeletal muscle characteristics in sedentary black and Caucasian males. 294 52


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