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)

Maximal in vitro activities of key metabolic enzymes were measured in brain and eye heaters of five species of scombroid fishes. Istiophorid billfishes (blue marlin, striped marlin and Mediterranean spearfish), xiphiid billfishes (Pacific and Mediterranean stocks) and a scombrid fish (butterfly mackerel) were included in the analysis. Our main objectives were (1) to assess the maximum possible substrate flux in heater tissue, and (2) to determine what metabolic substrates could fuel heat production. Heater tissue of all scombroids examined showed extremely high oxidative capacity. Activities of citrate synthase, a commonly measured index of oxidative metabolism, included the highest value ever reported for vertebrate tissue. In most billfishes, citrate synthase activities were similar to or higher than those found for mammalian cardiac and avian flight muscle. Marker enzymes for aerobic carbohydrate metabolism (hexokinase) and fatty acid metabolism (carnitine palmitoyltransferase and 3-hydroxyacyl-CoA dehydrogenase) also displayed extraordinarily high activities. Activities of carnitine palmitoyltransferase measured in heater organs were among the highest reported for vertebrates. These results indicate that heat production could be fueled aerobically by either lipid or carbohydrate metabolism. Inter- and intraspecifically, heater organs of fishes from the colder Mediterranean waters had a higher aerobic capacity and, hence, a greater heat-generating potential, than fishes from the warmer waters of the Pacific. This difference may be attributed to different thermal environments or it may result from allometry, since fishes caught in the Mediterranean were considerably smaller than those caught in the Pacific.
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PMID:Activities of key metabolic enzymes in the heater organs of scombroid fishes. 175 72

Hummingbirds in flight display the highest rates of aerobic metabolism known among vertebrates. Their flight muscles possess sufficient maximal activities of hexokinase and carnitine palmitoyltransferase to allow the exclusive use of either glucose or long-chain fatty acids as metabolic fuels during flight. Respiratory quotients (RQ = VCO2/VO2) indicate that fatty acid oxidation serves as the primary energy source in fasted resting birds, while subsequent foraging occurs with a rapid shift towards the use of carbohydrate as the metabolic fuel. We suggest that hummingbirds building up fat deposits in preparation for migration behave as carbohydrate maximizers (or fat minimizers) with respect to the metabolic fuels selected to power foraging flight.
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PMID:Fuel selection in rufous hummingbirds: ecological implications of metabolic biochemistry. 225 Dec 66

Concentrations of high-energy phosphates and activities of key enzymes of energy metabolism were assessed in hearts from species with differing levels of cardiac power output. Positive correlations were found between resting power output and the total adenylate pool and between citrate synthase activity and the total adenylate pool. Maximum in vitro activity levels of enzymes from energy metabolism were compared with calculated resting cardiac power output and maximal cardiac power output (as reflected by total oligomycin-insensitive adenosine-triphosphatase activity). Three indexes of carbohydrate metabolism (hexokinase, pyruvate kinase, and L-lactate dehydrogenase) all plateau at relatively low levels of energy demand. In contrast, enzymes required for aerobic fatty acid metabolism, (carnitine palmitoyltransferase and 3-hydroxyacyl-CoA dehydrogenase) and for tricarboxylic acid and electron transport (citrate synthase and cytochrome-c oxidase) show consistent increases as ATP demand is elevated. It appears that as capacity for power development by vertebrate hearts, increases across taxa, the elevated demand for ATP is met by expansion of fatty acid based aerobic metabolism and not carbohydrate metabolism.
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PMID:Matching of vertebrate cardiac energy demand to energy metabolism. 295 61

Maximum activities of some key enzymes of metabolism were studied in elicited (inflammatory) macrophages of the mouse and lymph-node lymphocytes of the rat. The activity of hexokinase in the macrophage is very high, as high as that in any other major tissue of the body, and higher than that of phosphorylase or 6-phosphofructokinase, suggesting that glucose is a more important fuel than glycogen and that the pentose phosphate pathway is also important in these cells. The latter suggestion is supported by the high activities of both glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase. However, the rate of glucose utilization by 'resting' macrophages incubated in vitro is less than the 10% of the activity of 6-phosphofructokinase: this suggests that the rate of glycolysis is increased dramatically during phagocytosis or increased secretory activity. The macrophages possess higher activities of citrate synthase and oxoglutarate dehydrogenase than do lymphocytes, suggesting that the tricarboxylic acid cycle may be important in energy generation in these cells. The activity of 3-oxoacid CoA-transferase is higher in the macrophage, but that of 3-hydroxybutyrate dehydrogenase is very much lower than those in the lymphocytes. The activity of carnitine palmitoyltransferase is higher in macrophages, suggesting that fatty acids as well as acetoacetate could provide acetyl-CoA as substrate for the tricarboxylic acid cycle. No detectable rate of acetoacetate or 3-hydroxybutyrate utilization was observed during incubation of resting macrophages, but that of oleate was 1.0 nmol/h per mg of protein or about 2.2% of the activity of palmitoyltransferase. The activity of glutaminase is about 4-fold higher in macrophages than in lymphocytes, which suggests that the rate of glutamine utilization could be very high. The rate of utilization of glutamine by resting incubated macrophages was similar to that reported for rat lymphocytes, but was considerably lower than the activity of glutaminase.
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PMID:Metabolism of glucose, glutamine, long-chain fatty acids and ketone bodies by murine macrophages. 380 Sep 71

Unequivocal demarcation between immature, nonmigratory yellow eels and migratory silver eels of greater sexual maturity is possible by measuring eye diameter and retinal capillary length, which undergo a 1.5- and 2.3-fold increase during metamorphosis, respectively. Anatomical arrangement of trunk musculature is similar in the two groups except for an increased depth of slow muscle in silver eel. Histochemical analysis reveals a progressive increase in numbers of "displaced" fast fibres within slow muscle of the lateral line triangle in maturing eels, although these are unlikely to affect recruitment pattern of muscle fibre types. Previous studies have suggested greater involvement of fast muscle in locomotion of migratory eels. In contrast, estimates of enzyme activity in fast muscle suggest an inadequate aerobic capacity to fuel sustained activity. Myoglobin content is extremely low, around 0.4 nM g wet wt-1. Prolonged anaerobic metabolism is also discounted as a migratory strategy. Increased energy provision for migration is apparently derived from increased capacity for both aerobic carbohydrate metabolism and mitochondrial fatty acid oxidation within slow muscle of silver eels. Activity of hexokinase (HK) shows a 1.6-fold increase (to 0.51 microM g wet wt-1) and carnitine palmitoyltransferase (CPT) a 3.1-fold increase (to 0.22 microM g wet wt-1 min-1), suggesting a maximal flux through these pathways of 18 and 14 ATP equivalents, respectively. However, the fatty acyl transferase system of skeletal muscle mitochondria displays up to threefold greater activity with palmitoleoyl CoA (C16:1) as substrate than with the usual palmitoyl CoA (C16:0). Slow muscle of silver eel is therefore capable of deriving aerobic energy from free fatty acids and carbohydrate in the ratio 2.3:1. Differences in aerobic enzyme activities are not paralleled by myoglobin content of slow muscle, being 15 and 16 nM g wet wt-1 for yellow and silver eel, respectively. Structural reorganization of muscle fibres during metamorphosis, however, results in a twofold elevation of cytoplasmic myoglobin concentration in silver eel. It would appear that dramatic differences in metabolic capacity between life history stages of eel is required to overcome locomotory inefficiency of yellow eels and to "preadapt" silver eels for migratory activity. This increased locomotory capacity may be amplified by a subsequent training response.
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PMID:Metamorphosis of the American eel, Anguilla rostrata LeSeur: I. Changes in metabolism of skeletal muscle. 395 May 63

Linoleate monohydroperoxide (L-HPO), methyl linoleate monohydroperoxide (ML-HPO), and methyl hydroperoxy-epoxy-octadecenoate (ML-X) inhibited state 3 respiration of mitochondria when palmitate, palmitoyl CoA, or L-palmitoylcarnitine was used as a substrate. L-HPO was the most effective, and 50% inhibition of palmitate-supported respiration was observed with 2, 3.3, and 6.5 nmol/mg protein of L-HPO, ML-X, and ML-HPO, respectively. Almost the same values were obtained when palmitoyl CoA or L-palmitoylcarnitine was used in place of palmitate. L-HPO inhibited the reaction of beta-oxidation in mitochondria in a similar concentration range (4 nmol/mg protein for 50% inhibition) when L-palmitoylcarnitine was used as a substrate. L-HPO also inhibited the formation of 3-hydroxypalmitoylcarnitine from the same substrate. Carnitine palmitoyltransferase activity of mitochondria was inhibited by L-HPO, 50% inhibition occurring at 12 nmol/mg protein. These inhibitory effects of L-HPO were weaker when ATP was removed by hexokinase and glucose. ATP-dependent formation of carnitine ester of L-HPO was also suggested. It was deduced that L-HPO (and ML-X and ML-HPO after hydrolysis) was converted to carnitine ester and inhibited the palmitate metabolism at the site(s) of intramitochondrial carnitine palmitoyltransferase (and possibly acyl CoA dehydrogenase).
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PMID:Inhibition of palmitate oxidation in mitochondria by lipid hydroperoxides. 672 34

1. Activities of 3-oxo acid CoA-transferase, D-3-hydroxybutyrate dehydrogenase, hexokinase and carnitine palmitoyltransferase have been measured in the gastrointestinal tract. 2. Activity of 3-oxo acid CoA-transferase in the glandular mucosa of the stomach was as high as that in heart and kidney, and was 2--4 times greater than that in other regions of the gastrointestinal tract. It is suggested that metabolism of acetoacetate might support acid secretion on re-feeding after a period without food. 3. All regions of the gastrointestinal tract have the capacity to use ketone bodies, and it is likely that both muscle and mucosa will contribute to their utilization. 4. Activity of hexokinase was twice the rate of glucose utilization by the jejunum under anaerobic conditions. The maximal rate of glucose metabolism in the jejunum may not be substantially different from that in other regions of the gastrointestinal tract. 5. Starvation decreased the capacity for metabolism of glucose in several regions of the intestine. 6. Activities of carnitine palmitolytransferase in the stomach, jejunum and colon were similar, and about one-third of that in the liver. Activity in the jejunum was much higher than the apparent rate of oxidation of exogenous fatty acid. 7. The results do not suggest any large variation between tissues of the gastrointestinal tract in metabolism of glucose or fatty acids, whereas metabolism of ketone bodies may be more prominent in the stomach.
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PMID:Activity of 3-oxo acid CoA-transferase, D-3-hydroxybutyrate dehydrogenase, hexokinase and carnitine palmitoyltransferase in the stomach and small and large intestine of the rat. 695 79

Preflight development of the goslings was typified by rapid increases in the mitochondrial enzymes of the semimembranosus and heart ventricular muscles resulting in near-adult values by 3 wk of age. In contrast, aerobic capacity of the pectoralis muscle initially developed slowly but showed a rapid increase between 5 and 7 wk of age, in preparation for becoming airborne. Activities of glycolytic enzymes in the pectoralis muscle showed similar patterns of development as those found for the aerobic enzymes, except for hexokinase, which was low at all ages, indicating an adaptation for catabolism of both intracellular glycogen and plasma fatty acids in preference to plasma glucose. Muscle mass specific activity of citrate synthase in the pectoralis increased by only 33% from goslings during the first few days of flight, compared with premigratory geese. Activities of anaerobic glycolytic enzymes in the ventricles were low, but values for hexokinase, which is involved in the phosphorylation of plasma glucose, developed rapidly. Values for lactate dehydrogenase were also high, reflecting the capacity of the heart to catabolize plasma lactate. Substrate flux supplied by carnitine palmitoyltransferase and oxoglutarate dehydrogenase (OGD), in the pectoralis muscles of the premigratory geese, appears to have the smallest excess capacities to meet the requirements of sustained aerobic flight. The average maximum oxygen uptake for premigratory geese during flight, as indicated by values for OGD, is calculated to be 484 ml O2/min (or 208 ml O2.min-1.kg-1).
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PMID:Development of metabolic enzyme activity in locomotor and cardiac muscles of the migratory barnacle goose. 2679 34

We examined effects of temperature acclimation on ultrastructural characteristics of cardiac myocytes and maximal activities of metabolic enzymes in cardiac tissue of striped bass (Morone saxatilis). Ventricular mass and ventricular mass divided by body weight were significantly increased (29% and 40%, respectively) in animals acclimated to cold (5 degrees C) vs. warm temperatures (25 degrees C). Mean myocyte diameter was increased at cold temperature (3.47 +/- 0.14 vs. 2.98 +/- 0.08 microns), which is sufficient to explain the increase in ventricular mass. Ventricular enlargement did not alter volume densities of mitochondria, myofibrils, protein concentration, or citrate synthase activity. Thus total volume of mitochondria and myofibrils increased proportionately with cardiac mass in cold animals. Activities of hexokinase (34%) and carnitine palmitoyltransferase (42%) increased in cold animals, suggesting positive compensation and increased aerobic capacity for utilization of glucose and fatty acids for energy production. Enlargement of the ventricle and an increased capacity for ATP production in striped bass may help compensate for kinetic constraints at cold temperatures and maintain circulatory support to oxidative axial musculature for swimming activity.
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PMID:Structural and biochemical analyses of cardiac ventricular enlargement in cold-acclimated striped bass. 924 57

The transport of activated fatty acids across the mitochondrial outer membrane has not been fully addressed. A polyanion (M(n)=22 kDa) inhibited the ADP-stimulated carnitine-dependent oxidation of both palmitoyl-CoA and palmitate plus CoA as well as mitochondrial hexokinase binding. In contrast, the oxidation of palmitoylcarnitine plus malate, as well as glutamate oxidation, was essentially unaffected. Mitochondrial carnitine palmitoyltransferase-1 was not inhibited by the polyanion. The data suggest an additional component in carnitine-dependent mitochondrial fatty acid oxidation, possibly porin.
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PMID:A 22 kDa polyanion inhibits carnitine-dependent fatty acid oxidation in rat liver mitochondria. 1054 43


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