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:2.3.3.1 (citrate synthase)
4,488 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cells of the aerotolerant anaerobe Giardia lamblia respire in the presence of oxygen. Endogenous respiration is stimulated by glucose but not by other carbohydrates and Krebs cycle intermediates. Endogenous and glucose-stimulated respiration are insensitive to cyanide, malonate, and 2,4-dinitrophenol, but are inhibited by atabrin and iodoacetamide. G. lamblia produces ethanol, acetate and CO2 both aerobically and anaerobically either from endogenous reserves or exogenous glucose. Molecular hydrogen is not produced. The following enzyme activities were detected in homogenates: hexokinase, fructose-biphosphate aldolase, pyruvate kinase, phosphoenolpyruvate carboxykinase, malate dehydrogenase, malate dehydrogenase (decarboxylating), pyruvate synthase, acetyl-CoA synthetase, alcohol dehydrogenase (NADP+), NADH dehydrogenase, NADPH dehydrogenase, NADPH oxidoreductase and superoxide dismutase. The enzymes of energy and carbohydrate metabolism are nonsedimentable (109 000 x g for 30 min). Activities of lactate dehydrogenase, hydrogenase, phosphate acetyltransferase, acetate kinase, citrate synthase, succinate dehydrogenase, fumarate hydratase and catalase were below the limits of detection. The results suggest the occurrence of glycolysis, energy production by substrate level phosphorylation and a flavin, iron-sulfur protein mediated electron transport system as well as the absence of cytochrome mediated oxidative phosphorylation and functional Krebs cycle.
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PMID:Energy metabolism of the anaerobic protozoon Giardia lamblia. 610 7

Burn injury is associated with an elevation in total body oxygen consumption, increased hepatic alanine uptake and conversion to glucose, and a negative nitrogen balance. The primary source of the alanine used for gluconeogenesis by the liver and of the nitrogen lost as urea is believed to be from skeletal muscle. Selected muscle regulatory enzymes and pyruvate and oleate oxidation rates were assayed for maximal activity during the postburn period. Male Sprague-Dawley rats that received 50% total body surface scald burns on the dorsum and abdomen were examined for citrate synthase (CS), phosphofructokinase (PFK), and glutamate-pyruvate transaminase (GPT) activity in uninjured muscle at 3, 7, 13, and 20 days postburn, and the ability of muscle to oxidize pyruvate and oleate was measured at 3 and 13 days after injury. Cs, PFK, and GPT activities increased significantly (p less than 0.05) by 13-20 days after injury in the soleus and diaphragm. The epitrochlearis showed no change in CS, but PFK and GPT were elevated within this time frame. The gastrocnemius muscle showed an elevated oleate oxidation rate at 13 days after injury, but no change at 3 days postburn. Pyruvate oxidation rates were unaltered. The results of this study indicate that during the postburn period several metabolic alterations occur in muscle. These adaptations include: (1) elevated CS activity which may be associated with increased oxidative capacity,, (2) increased PFK activity which implies that more substrate is being shuttled through the glycolytic pathway, (3) increased GPT activity which may reflect increased pyruvate conversion to alanine, and (4) increased oleate oxidation rates which demonstrate that muscle is utilizing more fatty acid substrates during the postburn period.
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PMID:Altered muscle metabolism in rats after thermal injury. 621 91

The effect of endurance training on skeletal muscle myoglobin concentration in man was investigated. 8 healthy sedentary males (20-31 yrs) trained on cycle ergometers 40 min/day, 4 days a week for 8 weeks. The work consisted of continuous exercise at a work load that during the last 5 weeks corresponded to 75% of the pretraining maximal oxygen uptake (VO2 max). The training program resulted in a 7% increase in VO2 max (p less than 0.01). The activities of the mitochondrial enzymes citrate synthase (CS), succinate dehydrogenase (SDH) and cytochrome c oxidase (Cyt-c-ox) in the quadriceps femoris muscle, as indicators of muscle respiratory capacity, increased by 62-82% (p less than 0.01). The metabolic adaptation of skeletal muscle was further indicated by a 17% increase in the work load corresponding to a blood lactate concentration of 4 mmol/l, as determined by a progressive exercise test (p less than 0.05). There was, however, no change in the myoglobin concentration of the thigh muscle with training (-1%, NS). It is suggested that endurance exercise in man at 75% of the maximal oxygen uptake does not severely tax the functions of myoglobin in skeletal muscle.
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PMID:Dissociation of training effects on skeletal muscle mitochondrial enzymes and myoglobin in man. 630 98

This study examines the structural relationship of mitochondria and the endoplasmic reticulum in liver. Livers of rat and Japanese quail were homogenized and fractionated in media of 0.25 M-sucrose, either 5mM or 50 mM in sodium Hepes [4-(2-hydroxyethyl)-1-piperazine-ethanesulphonic acid], pH 7.4 (2.2 mM or 22 mM in Na respectively), designated here as low- and high-salt media. Three particulate fractions were prepared by sequential centrifugation. A nuclear pellet sedimenting at 300 g was obtained as described by Shore & Tata [(1977) J. Cell Biol. 72, 714-725], and from the resulting supernatant thereof a low-speed pellet (1100-1500 g) and a high-speed pellet (8000-10 000 g) were prepared. In the low-salt medium the yields of mitochondrial matrix enzymes (citrate synthase, glutamate dehydrogenase, ornithine carbamoyltransferase) and their specific activities in the low-speed pellet were over twice those in the high-speed pellet. In the high-salt medium the yield of matrix enzymes was 4-5 times, and the specific activities were up to 3 times, higher in the low-speed pellet than in the high-speed pellet. Oxygen uptake and respiratory control ratio were also much higher in the low-speed pellets in both media. Some 50-65% of the microsomal marker enzyme glucose 6-phosphatase was in the supernatant from the high-speed pellet, and the rest sedimented with the mitochondria. Repeated washing with the high-salt medium removes only a limited amount of reticulum. Washing with salt-free sucrose removes most of the reticulum, but a fraction remains strongly bound to mitochondria. Homogenates from quail and rat liver were fractioned isopycnically on Percoll gradients in either 0.25 M-sucrose or 0.25 M-sucrose/50 mM-sodium Hepes. Up to five particulate bands were separated and assayed. Mitochondria were present in two to three bands and were associated with endoplasmic reticulum. As seen in the phase-contrast microscope the mitochondria prepared in the low-salt medium consist of separate organelles. In the high-salt medium the mitochondria appear as chains of from three to ten organelles not touching each other. On addition of univalent ions at concentrations above 20 mM, the mitochondria aggregate into chains, and at higher ionic strength larger multidimensional aggregates are formed. The dispersion and aggregation of mitochondria are reversible. Negatively stained electron micrographs reveal a branched mitochondrial structure, with mitochondria held together by strands of reticulum.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Mitochondrial-reticular cytostructure in liver cells. 635 78

The effects of physical training on skeletal muscle morphology and enzyme activities were compared in 10 male, type I diabetic subjects and 10 healthy, male, control subjects. The training program consisted of running for 45 min, three times per week for 8 wk. Muscle biopsies were obtained before and after the training period from the lateral portion of the gastrocnemius muscle. Pretraining maximal oxygen uptake was similar in the two groups (diabetic subjects 42 +/- 1 versus control subjects 43 +/- 2 ml X kg-1 X min-1), and the training resulted in an identical increase (+ 13%, P less than 0.01). Muscle capillarization (number of capillaries per muscle fiber) increased on the average in the control group (+ 14 +/- 4%, P less than 0.01), but was unchanged in the diabetic group (0 +/- 4%). Capillary density, expressed as number of capillaries per unit muscle cross sectional area, also increased on the average in controls (8 +/- 4%, P less than 0.05) but failed to do so in the diabetic patients (-8 +/- 6%, NS). The activities of the mitochondrial enzymes citrate synthase (+ 26-27%, P less than 0.01-0.05) and succinate dehydrogenase (+ 24-25%, P less than 0.05) increased significantly and similarly in the two groups, whereas training did not result in significant changes in the activities of the glycolytic enzymes 6-phosphofructokinase and glyceraldehyde-phosphate dehydrogenase. Glycemic control in the diabetic group did not improve with the training, as evaluated from hemoglobin A1 and home-monitored blood glucose.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Influence of physical training on formation of muscle capillaries in type I diabetes. 646 66

Long-term electrical stimulation (14-28 days) of rabbit fast muscles (tibialis anterior, TA and extensor digitorum longus, EDL) using intermittent high frequency (3 trains per min of 5 s duration at 40 Hz, for 8 h per day) produced changes in enzyme activities similar to those found with continuous stimulation at a frequency occurring in nerves to slow muscles (10 Hz). The activity of citrate synthetase, 3-hydroxyacyl-CoA dehydrogenase and succinate dehydrogenase increased two to 3-fold within 28 days. There was a 4-fold increase in hexokinase whereas phosphofructokinase, pyruvate kinase, lactate dehydrogenase and fructose-1,6-diphosphatase decreased to about 60% of the activity levels in the contralateral unstimulated muscles. Blood flow and oxygen consumption at rest were not changed even after 28 days of stimulation, but were increased during contractions in muscles stimulated at either frequency, the level being twice as high as in control muscles. Glucose uptake was similar to that in control muscles both at rest and during contractions and the output of lactate was similar to that found in control muscles in muscles stimulated at 40 Hz. Muscles stimulated at 10 Hz had smaller lactate output. Thus intermittent stimulation at high frequency (40 Hz) and continuous low frequency (10 Hz) produced similar changes in aerobic metabolism and fuel uptake provided that the total number of stimuli was comparable and that the stimulation was carried out for sufficiently long period.
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PMID:Effects of different patterns of long-term stimulation on blood flow, fuel uptake and enzyme activities in rabbit fast skeletal muscles. 652 41

Myoglobin, muscle fibre diameter, and citrate synthase activity were measured in leg muscle of untrained and trained men and in the myocardium from the apex of the left ventricle and from papillary muscle in patients subjected to open heart surgery. The citrate synthase (CS) activity was 60% higher in trained than in untrained skeletal muscle. In the myocardium it was around four times greater than in untrained skeletal muscle but there was no difference between the apex of the left ventricle and papillary muscle. The fibre diameter varied almost threefold between the different groups of muscles with the largest diameter in untrained skeletal muscle and the with the largest diameter in untrained skeletal muscle and the smallest in papillary muscle. The myoglobin content in trained skeletal muscle did not differ from that of untrained muscle. In the left ventricle it was only 40% of that found in untrained muscle while papillary muscle had almost twice as high a myoglobin content as did the left ventricle. The ratio between myoglobin and fibre diameter, however, was of similar magnitude in skeletal muscle and the left ventricle while it was twice as high in papillary muscle as in the other muscles. In conclusion, the diffusion distance in terms of fibre diameter decreased with increased oxidative capacity (CS activity), when comparing the statistical means of the four different groups. The capacity for oxygen diffusion in relation to oxygen demand measured as the ratio of myoglobin to fibre diameter appeared to be of similar magnitude in skeletal muscle and left ventricle but was higher in papillary muscle.
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PMID:Myoglobin content in human skeletal muscle and myocardium: relation to fibre size and oxidative capacity. 674 65

Since little is known about the training response to exercise in neonatal animals, this study was undertaken to elucidate the potential of oxidative system adaptations in developing skeletal muscle of rats during 50 days of daily treadmill running. The training regimen involved male and female rats (10 days old) initially running 0.1 mph, 0% grade, for 15 min. The program progressed to 1 mph, 25% grade, for 60 min by 50 days of age. At 25 days of age, pyruvate and palmitate oxidative capacity, and citrate synthase activity in red vastus muscle homogenates were elevated in the trained group (T) compared with age- and sex-matched controls (C). These increases were also observed for each subsequent time point tested and occurred in spite of the fact that the peak oxidative capacity of neonatal red vastus muscle was 46% greater than adult values. Further, trained animals tested at 45 days of age responded with a 12% increase in maximal oxygen consumption (Vo2max) compared with controls (P less than 0.05). Assays of muscle phosphofructokinase and of creatine phosphokinase activity conducted at this time point revealed no difference between T and C groups. Collectively, these data suggest that neonatal rats can be successfully trained and that they respond to an endurance-type program qualitatively similarly to adult rats.
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PMID:Effects of repetitive exercise on neonatal rat skeletal muscle oxidative capacity. 683 49

Catecholamine-induced thermogenesis is significantly diminished in BIO 14.6 cardiomyopathic hamsters as demonstrated by a reduced increase in oxygen consumption of these hamsters in response to administered isoproterenol. This decreased responsiveness is accompanied by a reduction in the amount of brown adipose tissue, a major nonshivering thermogenic effector. The present study demonstrates that the metabolic responses of individual brown fat cells are also altered in the dystrophic hamster. That is, 1 microM norepinephrine, the physiological mediator of nonshivering thermogenesis, evoked rates of oxygen consumption that were significantly lower in brown adipocytes isolated from the BIO 14.6 hamsters than in those from normal controls. Additionally, the dystrophic adipocytes exhibited: decreased maximal activity (per cell as well as per milligram protein) of citrate synthase; decreased cell size; and decreased amounts of protein per cell. These data indicate that the nonshivering thermogenic capacity of the intact BIO 14.6 hamsters reflects altered characteristics of the individual brown adipocytes themselves, as well as decreased amounts of the tissue.
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PMID:Diminished respiratory responses of brown adipocytes isolated from BIO 14.6 dystrophic hamsters. 685 20

Oxidative metabolism and citrate synthase activity during the perinatal period were assessed in isolated rabbit heart mitochondria at 27 days' gestation (27 dpc), 1 day postpartum (1 dpp) and 10 dpp. Oxygen consumption was measured during state 3 and state 4 respiration using the following substrates: glutamate, alpha-ketoglutarate, pyruvate/malate, succinate/rotenone, acetate, palmitylcarnitine, and palmityl CoA/carnitine. Results obtained from fetal and neonatal animals were compared to values obtained from adult left and right ventricles. Rates of state 3 oxygen consumption per milligram mitochondrial protein using tricarboxylic acid cycle intermediates or palmitylcarnitine were higher in both 1 and 10 dpp animals than in either left or right ventricles. Respiratory activity per milligram mitochondrial protein using these substrates was similar in 27 dpc fetuses and adult left ventricles. The rate of oxidation of palmityl CoA was lower in fetal mitochondria than in adult left ventricle, indicating that the capacity for conversion of long-chain fatty acyl CoA to acylcarnitine necessary for transport of fatty substrates into the mitochondria is decreased in fetal hearts. Increases in myocardial citrate synthase corresponded to increases in mitochondrial mass reported by other investigators.
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PMID:Perinatal changes in mitochondrial respiration of the rabbit heart. 689 4


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