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)

This study examined whether training under normobaric hypoxic conditions (simulating medium level altitude) would enhance physical performance and selected muscle adaptations over and above that which occurs with normoxic training. Ten healthy males (19-25 yr) underwent 8 wk of unilateral cycle ergometry training so that one leg was trained while breathing an inspirate of 13.5% O2 and the other while breathing normal ambient air. Pre- and post-training measurements included single leg VO2max and time to fatigue at 95% VO2max. Needle biopsies from quadriceps were assayed for oxidative and glycolytic enzyme activity and analyzed for capillary density, fiber area, % fiber type, and mitochondrial and lipid volume density. VO2max, time to fatigue, citrate synthase (CS), succinate dehydrogenase, and phosphofructokinase activity increased significantly (P > 0.05) in both legs following training. The increase in CS activity in the hypoxically trained leg was also significantly greater than that in the normoxically trained leg. It thus appears that training under moderate normobaric hypoxic conditions enhances muscle citrate synthase activity to a greater extent than training under normoxic conditions.
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PMID:Skeletal muscle adaptations to training under normobaric hypoxic versus normoxic conditions. 904 29

The insulin resistance of skeletal muscle in glucose-tolerant obese individuals is associated with reduced activity of oxidative enzymes and a disproportionate increase in activity of glycolytic enzymes. Because non-insulin-dependent diabetes mellitus (NIDDM) is a disorder characterized by even more severe insulin resistance of skeletal muscle and because many individuals with NIDDM are obese, the present study was undertaken to examine whether decreased oxidative and increased glycolytic enzyme activities are also present in NIDDM. Percutaneous biopsy of vatus lateralis muscle was obtained in eight lean (L) and eight obese (O) nondiabetic subjects and in eight obese NIDDM subjects and was assayed for marker enzymes of the glycolytic [phosphofructokinase, glyceraldehyde phosphate dehydrogenase, hexokinase (HK)] and oxidative pathways [citrate synthase (CS), cytochrome-c oxidase], as well as for a glycogenolytic enzyme (glycogen phosphorylase) and a marker of anaerobic ATP resynthesis (creatine kinase). Insulin sensitivity was measured by using the euglycemic clamp technique. Activity for glycolytic enzymes (phosphofructokinase, glyceraldehye phosphate dehydrogenase, HK) was highest in subjects with subjects with NIDDM, following the order of NIDDM > O > L, whereas maximum velocity for oxidative enzymes (CS, cytochrome-c oxidase) was lowest in subjects with NIDDM. The ratio between glycolytic and oxidative enzyme activities within skeletal muscle correlated negatively with insulin sensitivity. The HK/CS ratio had the strongest correlation (r = -0.60, P < 0.01) with insulin sensitivity. In summary, an imbalance between glycolytic and oxidative enzyme capacities is present in NIDDM subjects and is more severe than in obese or lean glucose-tolerant subjects. The altered ratio between glycolytic and oxidative enzyme activities found in skeletal muscle of individuals with NIDDM suggests that a dysregulation between mitochondrial oxidative capacity and capacity for glycolysis is an important component of the expression of insulin resistance.
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PMID:Altered glycolytic and oxidative capacities of skeletal muscle contribute to insulin resistance in NIDDM. 921 60

These experiments compared oxidative and glycolytic enzyme activity in the costal and crural diaphragm in seven adult mammals (mouse, rat, rabbit, ferret, sheep, pig, cow) ranging in body mass from approximately 0.03 to 422 kg. Segments of the costal and crural diaphragm from the aforementioned species were homogenized to determine the activities of the glycolytic enzyme, lactate dehydrogenase (LDH), and the Krebs cycle enzyme, citrate synthase (CS). The results indicated that metabolic differences between the costal and crural diaphragm do not exist in all mammalian species. Specifically, CS activity differed (P < 0.05) between the costal and crural diaphragm (costal approximately 36% greater than crural) in only two species (rat and rabbit). Further, the oxidative capacity of the costal and crural diaphragm was significantly correlated with both breathing frequency and resting metabolic rate (r = 0.92 - 0.57; P < 0.05) across the species investigated. In contrast, glycolytic capacity was not significantly correlated (P > 0.05) with either breathing frequency or resting metabolic rate.
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PMID:Bioenergetic characteristics of the costal and crural diaphragm in mammals. 929 46

The effect of physical conditioning on skeletal muscle of individuals with spinal cord injuries (SCI) has been investigated. The anterior portion of the deltoid muscle (active in wheel-chair propulsion) of untrained and endurance-trained paraplegics and tetraplegics, as well as that of untrained able-bodied subjects, was studied. The characterization involved fibre type distribution, capillarization, fibre areas and also oxidative and glycolytic enzyme levels. A general trend towards a successively higher proportion of type I fibres and lower proportion of type IIB fibres was noted in the order of able-bodied subjects (type I, 42%; type IIB, 41%, n = 8), paraplegics (type I, 57%; type IIB, 13%, n = 13) and tetraplegics (type I, 74%; type IIB, 4.5%, n = 11). The trained SCI groups had significantly higher levels of the citric acid cycle marker enzyme citrate synthase (34% and 63%) than the untrained SCI groups and able-bodied subjects, respectively. The glycolytic marker enzyme 6-phosphofructokinase was 32% lower in the tetraplegic groups than in the other groups. In contrast, the fatty acid oxidation marker enzyme 3-hydroxyacyl-CoA dehydrogenase was markedly higher in the tetraplegic group than in the able-bodied subjects (58%) and tended to be higher (21%, P < 0.1) than in the paraplegic group. The trained SCI groups displayed significantly higher (28%) levels of capillaries per fibre than the untrained SCI groups, which had about the same levels as the untrained able-bodied subjects. It is concluded that several of the findings are in line with normal muscular adaptation, whereas others are unexpected and support a hypothesis that some of the findings might be due to differences between the groups in, for instance, hormone levels or in types of muscular load.
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PMID:Skeletal muscle of trained and untrained paraplegics and tetraplegics. 938 47

These experiments examined the myosin phenotype and bioenergetic enzyme activities in rat respiratory muscles. Muscle samples were removed from adult female Sprague-Dawley rats (N = 8) and analyzed to determine the myosin heavy chain (MHC) and light chain (MLC) isoform content as well as the activities of myofibrillar ATPase (mATPase), citrate synthase (CS; Krebs cycle enzyme), and lactate dehydrogenase (LDH; glycolytic enzyme). Analysis revealed that CS activity and the % type I MHC and %IId MHC isoforms were greater in the costal diaphragm (CO-D) compared with those in the crural diaphragm (CR-D). In contrast, the % type IIb MHC was higher in the CR-D compared with that in the CO-D. LDH and mATPase activity were lower in both the CO-D and CR-D compared with that in the parasternal intercostals (PI), external intercostals (EI), internal intercostals (II), rectus abdominis (RA), and sternomastoid (SM) muscles. CS activity, % type I MHC, %IIa MHC, and the ratio of slow to total alkali MLC (1s/1s + 1f + 3f) were greater in the CO-D and CR-D compared with those in all other respiratory muscles. The RA contained the highest (P < 0.05) % type IIb MHC and lowest CS activity compared with that in all other muscles. Finally, CS activity, mATPase activity, and MHC phenotype did not differ among the PI, EI, II, and SM muscles. These differences in biochemical properties provide the muscles of the respiratory pump with great versatility in functional properties.
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PMID:Myosin phenotype and bioenergetic characteristics of rat respiratory muscles. 943 89

Lung transplant (LTx) recipients have a low peak work rate, peak oxygen consumption (V O2peak), and early lactate threshold on incremental exercise. We hypothesized that LTx recipients have reduced oxidative function and altered fiber type proportion in peripheral skeletal muscle. Seven stable LTx recipients and seven age- and sex-matched control subjects were studied. Incremental exercise testing with arterialized venous sampling and a resting quadriceps femoris punch muscle biopsy were performed. Muscle specimens were analyzed for fiber type proportion, metabolites, oxidative and glycolytic enzyme activities, and mitochondrial ATP production rate (MAPR) using standard techniques. The results showed that mean V O2peak in LTx recipients was 52% of control subjects. Compared with the control subjects, LTx skeletal muscle exhibited: (1) a lower MAPR; (2) lower activity of the mitochondrial enzymes glutamate dehydrogenase (GDH), citrate synthase (CS), 2-oxogluterate dehydrogenase (OGDH), and 3-hydroxyacyl-CoA-dehydrogenase (HAD). There was no difference in the activities of anaerobic enzymes, except for higher phosphofructokinase activity; (3) a lower proportion of type I fibers; (4) a higher lactate and inosine monophosphate (IMP) content and a lower ATP content at rest indicating a high reliance on anaerobic metabolism. The reduced type I fiber proportion and severely reduced mitochondrial oxidative capacity may play an important role in exercise limitation after LTx.
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PMID:Skeletal muscle oxidative capacity, fiber type, and metabolites after lung transplantation. 1039 Mar 80

The effects of cell age on metabolism in the nucleated red blood cells of rainbow trout (Oncorhynchus mykiss) were examined. Red blood cells were separated according to age using fixed-angle centrifugation. The mean erythrocyte haemoglobin concentration in old red blood cells was found to be 120 % of that in young red blood cells. In young red blood cells, the activities of the mitochondrial enzymes citrate synthase and cytochrome oxidase were 135-200 %, respectively, of those measured in old red blood cells. The activity of the glycolytic enzyme lactate dehydrogenase in young red blood cells was 170 % of that in old red blood cells, whereas the activity of the glycolytic enzyme pyruvate kinase was not significantly affected by cell age. In addition, young red blood cells consumed over twice as much O(2) and devoted 50 % more O(2) to protein synthesis and the activity of Na(+)/K(+)-ATPase than old red blood cells. Red blood cell age did not significantly affect the rate of lactate production. This study shows that ageing in rainbow trout nucleated red blood cells is accompanied by a significant decline in aerobic energy production and the processes it supports, as well as a corresponding increase in the glycolytic contribution to metabolism.
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PMID:The effects of cell ageing on metabolism in rainbow trout (Oncorhynchus mykiss) red blood cells. 1068 63

Selective breeding is an important tool in behavioral genetics and evolutionary physiology, but it has rarely been applied to the study of exercise physiology. We are using artificial selection for increased wheel-running behavior to study the correlated evolution of locomotor activity and physiological determinants of exercise capacity in house mice. We studied enzyme activities and their response to voluntary wheel running in mixed hindlimb muscles of mice from generation 14, at which time individuals from selected lines ran more than twice as many revolutions per day as those from control (unselected) lines. Beginning at weaning and for 8 wk, we housed mice from each of four replicate selected lines and four replicate control lines with access to wheels that were free to rotate (wheel-access group) or locked (sedentary group). Among sedentary animals, mice from selected lines did not exhibit a general increase in aerobic capacities: no mitochondrial [except pyruvate dehydrogenase (PDH)] or glycolytic enzyme activity was significantly (P < 0.05) higher than in control mice. Sedentary mice from the selected lines exhibited a trend for higher muscle aerobic capacities, as indicated by higher levels of mitochondrial (cytochrome-c oxidase, carnitine palmitoyltransferase, citrate synthase, and PDH) and glycolytic (hexokinase and phosphofructokinase) enzymes, with concomitant lower anaerobic capacities, as indicated by lactate dehydrogenase (especially in male mice). Consistent with previous studies of endurance training in rats via voluntary wheel running or forced treadmill exercise, cytochrome-c oxidase, citrate synthase, and carnitine palmitoyltransferase activity increased in the wheel-access groups for both genders; hexokinase also increased in both genders. Some enzymes showed gender-specific responses: PDH and lactate dehydrogenase increased in wheel-access male but not female mice, and glycogen phosphorylase decreased in female but not in male mice. Two-way analysis of covariance revealed significant interactions between line type and activity group; for several enzymes, activities showed greater changes in mice from selected lines, presumably because such mice ran more revolutions per day and at greater velocities. Thus genetic selection for increased voluntary wheel running did not reduce the capability of muscle aerobic capacity to respond to training.
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PMID:Effects of voluntary activity and genetic selection on muscle metabolic capacities in house mice Mus domesticus. 1100 2

To establish whether family origin affects the response of the threespine stickleback (Gasterosteus aculeatus) to thermal acclimation, we examined the rates of feeding, growth, and food conversion, relative tissue and organ masses and activities of a mitochondrial and a glycolytic enzyme in pectoral and axial muscle of individually housed fish from six families during acclimation to 8 degrees C and 23 degrees C. Feeding rates differed among families but were consistently higher in warm-acclimated than cold-acclimated fish. Growth rates differed among families. In four families growth was greater at 8 degrees C; these families generally had higher conversion efficiencies at 8 degrees C than 23 degrees C. For two families, growth was greater at 23 degrees C than 8 degrees C and conversion efficiencies did not differ between 8 degrees C and 23 degrees C. Relative tissue and organ masses (percent axial muscle, hepatosomatic, gut and kidney indices) differed with gender and among families (hepatosomatic, gut and kidney indices) but little with acclimation status. In all families and in both muscles, activities of the mitochondrial enzyme, citrate synthase (CS), were increased by cold acclimation. Axial muscle levels of the glycolytic enzyme, lactate dehydrogenase (LDH), were not affected by thermal acclimation or family origin, but were strongly correlated with the hepatosomatic index and axial muscle protein content. Pectoral muscle levels of LDH were affected by family origin which also influenced the response to thermal acclimation. Similar patterns were observed for specific activities and total muscle contents of these enzymes. Stickleback family origin influenced rates of feeding and growth and the thermal sensitivity of growth rates but not the compensatory increase in muscle CS levels with cold acclimation. The differing thermal sensitivities of growth could reflect distinct strategies for the timing of juvenile growth.
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PMID:Family origin and the response of threespine stickleback, Gasterosteus aculeatus, to thermal acclimation. 1130 36

The fuels used by the hawkmoth Amphion floridensis to power flight are determined by nectar-feeding, with fed moths using primarily carbohydrate and unfed moths using primarily fat. To investigate the metabolic pathways underlying fuel-use flexibility in this species, we measured the maximal activities of several key metabolic enzymes in the flight muscle of fed and unfed individuals, for which metabolic rates and fuel utilization had been previously determined. Hexokinase (HK) and phosphofructokinase (PFK) occur at high activities and, during carbohydrate-fueled flight, are estimated to operate at fractional velocities comparable to those of exclusively carbohydrate-utilizing insects. Females exhibited higher glycolytic enzyme activities than did males, and males regulated PFK activity according to nectar feeding. Although beta-hydroxyacyl-CoA dehydrogenase (HOAD) was found at high activities, carnitine palmitoyl transferase (CPT) was not detectable, suggesting that fatty acids may be utilized via a carnitine-independent pathway during flight. Principal component analysis revealed a tendency for the activities of citrate synthase, HK, PFK, and HOAD to be positively correlated among individuals, as well as a lesser tendency for the activities of glycolytic vs. mitochondrial enzymes to be negatively correlated with each other. However, the principal components did not correlate with variation in either oxygen consumption rate or fuel use in vivo, suggesting that variation in enzyme concentration did not determine differences among individuals in metabolic performance during flight. J. Exp. Zool. 290:108-114, 2001.
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PMID:Fuel use in hawkmoth (Amphion floridensis) flight muscle: enzyme activities and flux rates. 1147 Nov 40


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