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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)

The effect of thermal acclimation on the activity of carnitine palmitoyltransferase I (CPT I), the rate-limiting enzyme for beta-oxidation of long-chain fatty acids, was determined in oxidative red muscle of striped bass (Morone saxatilis) acclimated at 5 or 25 degrees C. As observed in mammalian tissues, malonyl-CoA potently inhibited CPT I activity of mitochondria. Inhibition by malonyl-CoA required inclusions of both bovine serum albumin (BSA) and palmitoyl-CoA in the reaction media. Because BSA binds long-chain fatty acyl-CoAs, this observation suggests that free fatty acyl-CoAs may disrupt mitochondrial membranes and affect the CPT I protein. Cold acclimation increased citrate synthase activity 1.6-fold and total CPT activity 2-fold in homogenates of red muscle; free carnitine increased 62%, and specific activity of CPT I in mitochondria increased 2-fold. No differences were observed between cold- and warm-acclimated fish in substrate-binding properties of CPT I at an assay temperature of 15 degrees C, as judged by the Michaelis constant (Km) for carnitine (0.11 +/- 0.02 vs. 0.13 +/- 0.02 mM) or inhibition of CPT I, as determined by the half-maximal inhibition concentration (IC50) for malonyl-CoA (0.14 +/- 0.05 vs. 0.09 +/- 0.03 microM). Thermal sensitivity of CPT I (Q10 = 2.91 +/- 0.12 vs. 3.02 +/- 0.20) and preference of CPT I for different long-chain fatty acyl-CoA substrates (16:1-CoA = 16:0-CoA > 18:1-CoA) were not altered by thermal acclimation.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Cold acclimation increases carnitine palmitoyltransferase I activity in oxidative muscle of striped bass. 814 97

We examined the effect of long-term intermittent cold exposure on the fiber type composition of the predominantly type I soleus and the predominantly type IIb extensor digitorum longus (EDL) muscles of rats. Cold exposure was accomplished by submerging the rats in shoulder-deep water, maintained at 20 +/- 0.5 degrees C, for 1 h/day, 5 days/wk, for < or = 19 wk. The efficacy of the treatment was tested by subjecting both groups to 20 degrees C water for 45 min while rectal temperature (Tre) and O2 consumption (VO2) were measured. The cold-exposed group displayed a 22% smaller reduction in Tre (P < 0.05) at the end of the exposure and 23% greater VO2 (P < 0.05) during the same period. Fiber type composition was determined using routine histochemical methods for myosin-adenosinetriphosphatase. In the soleus muscle of the cold-exposed rats, the number of type IIa fibers increased 156% (P < 0.05) and the number of type I fibers decreased 24% (P < 0.05). Cold exposure had no significant influence on the fiber type composition of the EDL muscle. Cold exposure resulted in an increase in citrate synthase activity of 20 and 22% in the soleus and EDL muscles, respectively (P < 0.05). The present study demonstrates that intermittent cold exposure induces a type I-to-type IIa transformation in the soleus muscle while having no influence on the EDL muscle.
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PMID:Intermittent cold exposure causes a muscle-specific shift in the fiber type composition in rats. 837 71

This investigation studied the importance of the rise in body temperature during exercise for aerobic capacity adaptations produced by endurance training. The approach used was to compare training effects produced by subjects exercising in hot (35 degrees C) water vs. cold (20 degrees C) water. Hot water was used to potentiate, and cold water to blunt, the rise in body temperature during exercise. Eighteen young men trained by cycle-ergometer exercise at 60% of maximal oxygen uptake (VO2max) while immersed to the neck in either hot (HWT, n = 9) or cold (CWT, n = 9) water for 60 min, 5 days/wk, for 8 wk. Before and after training, VO2max, erythrocyte volume, plasma volume, and vastus lateralis citrate synthase activity were measured. Training increased (P < 0.01) VO2max by 13%, with no difference between HWT and CWT in the magnitude of the effect. Erythrocyte volume increased 4% (P < 0.01) with training, with no difference between HWT and CWT in the magnitude of the effect. Plasma volume remained unchanged by training in both the HWT and CWT groups. Last, vastus lateralis citrate synthase activity increased by 38% with training, but there was no difference between HWT and CWT in the training effect. Thus, exercise-induced body temperature elevations are not an important stimulus for the aerobic adaptations to moderate-intensity endurance training.
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PMID:Role of thermal factors on aerobic capacity improvements with endurance training. 837

Bladder outlet obstruction induces severe changes in urinary bladder function and metabolism. These changes are characterized by significant reductions in the ability of the in vitro whole bladder to generate pressure and to empty. Metabolically, partial outlet obstruction induces a shift from oxidative to anaerobic metabolism. The decreased oxidative metabolism is mediated in part by significant decreases in mitochondrial substrate metabolism, which in turn is correlated with decreased activity of 2 important mitochondrial enzymes: citrate synthase and malate dehydrogenase. The present study was designed to evaluate mitochondrial function by studying the incorporation of 14C-adenine into high-energy phosphates (ATP, AMP, and ADP). Mild partial outlet obstructions were created by surgically placing silk ligatures loosely around the bladder neck. The results of these studies demonstrate that after 60 min incubation in oxygenated medium containing glucose + 1uCi14C-adenine, 1) There was no significant differences in the total AMP, ADP, and ATP concentrations measured in bladders taken from controls, 7- and 14-day obstructed rabbits; 2) there was no effect of obstruction on either the concentration of 14C-AMP in the tissue or in the ratio of hot to cold AMP; and 3) there was a 50% decrease in the concentration of 14C-ADP and a 70% decrease in the concentration of 14C-ATP in the bladder smooth muscle obtained from obstructed tissue (from both 7- and 14-day obstructions) compared to concentration in the control bladder smooth muscle. These results confirm the previous finding that obstruction did not reduce the rate of incorporation of adenine to AMP within the obstructed bladder smooth muscle and extends these studies to identify a significant reduction in the synthesis of both ADP and ATP. These results support the hypothesis that partial outlet obstruction induce a major dysfunction in mitochondrial function, both in the ability to oxidize substrates and in the ability to generate ATP.
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PMID:Effect of partial outlet obstruction on 14C-adenine incorporation in the rabbit urinary bladder. 913 42

We measured enzyme activities along a heterothermic tissue, the visceral retia mirabilia of the bluefin tuna, to test current theories of enzyme temperature adaptation. The heterothermic tissue model is ideal for the study of fundamental temperature adaptation because it eliminates confounding effects of whole animal acclimation. Enzymes were measured at six positions along the rete at four temperatures (15, 20, 25, and 30 degrees C). Five enzymes (aspartate aminotransferase, citrate synthase, glucose-6-phosphate dehydrogenase, glutamate dehydrogenase, and pyruvate kinase) exhibited a significant positive compensatory effect, with activity at the cold end of the rete 1.2-3.1 times higher than at the warm end. Two enzymes (alanine aminotransferase and lactate dehydrogenase) exhibited no significant compensation. On the basis of activation energies of enzymes along the rete, differences in activity were due to differences in enzyme concentration and not isozymes or enzyme modification. Analysis of the compensatory responses of the enzymes in light of their thermal sensitivities leads us to conclude that the pentose phosphate shunt is especially enhanced at the cold end of the rete.
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PMID:Enzyme adaptation along a heterothermic tissue: the visceral retia mirabilia of the bluefin tuna. 922 97

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 gene encoding citrate synthase from a novel bacterial isolate (DS2-3R) from Antarctica has been cloned, sequenced and over expressed in Escherichia coli. Both the recombinant enzyme and the native enzyme, purified from DS2-3R, are cold-active, with a temperature optimum of 31 degrees C. In addition the enzymes are rapidly inactivated at 45 degrees C, and show significant activity at 10 degrees C and below. Comparison of amino acid sequences indicates that DS2-3R citrate synthase is most closely related to the enzyme from gram-positive bacteria. The amino acid sequence of the DS2-3R enzyme shows several features previously recognised in other cold-active enzymes, including an extended surface loop, an increase in the occurrence of charged residues and a decrease in the number of proline residues in loops. Other changes observed in some psychrophilic enzymes, such as a decrease in isoleucine content and in arginine/(arginine+lysine) content, were not seen in this case.
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PMID:Sequencing and expression of the gene encoding a cold-active citrate synthase from an Antarctic bacterium, strain DS2-3R. 931 Mar 59

Recombinant citrate synthase from a psychrotolerant bacterium, DS2-3R, recently isolated in Antarctica, has been crystallized. The crystals belong to space group P6122 or P6522, with cell dimensions a = b = 70.8, c = 307.8 A. Diffraction data collected on a synchrotron from a cryoprotected crystal extends to at least 2.0 A. Knowledge of the structure of this enzyme will add to the understanding of cold activity and thermolability, and will be of biotechnological interest. Previously, the structure of citrate synthase from Archaea inhabiting environments at 328 and 373 K, has been reported. This present study will extend our understanding of the structural integrity and activity of proteins at the temperature extremes of life.
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PMID:Preliminary crystallographic studies of citrate synthase from an Antarctic psychrotolerant bacterium. 975 23

Developmental energetics of an Antarctic sea urchin, Sterechinus neumayeri, were quantified to describe the physiological bases underlying ontogenetic changes in metabolic rate at extreme cold temperatures (-1.5 degrees C). Rates of development from a four-arm to a six-arm larval stage were not affected by food availability. The respiratory cost of development to the six-arm larval stage (day 60) was 14.0 mJ for fed larvae and 8.2 mJ for unfed larvae. We observed three phases of metabolic regulation during development. During embryogenesis (day 0-22), increasing metabolic rates were proportional to increases in cell numbers. During early larval development (day 22-47), the differences in respiratory rate between fed and unfed larvae were not accounted for by cell number, but by cell-specific metabolic rate (respiratory rate normalized to DNA content). Once an advanced larval stage had been reached (day 47-60), cell-specific respiratory rate and mitochondrial densities (citrate synthase activity normalized to DNA content) were more equivalent between fed and unfed larvae, suggesting that size-specific metabolic rates were determined at a level of physiological regulation that was independent of cell numbers or feeding history.
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PMID:Energy metabolism during embryonic development and larval growth of an Antarctic sea urchin. 1039 19

The two species of isopods, Idotea baltica (Pallas) and Idotea emarginata (Fabricius), co-occur frequently near Helgoland, North Sea, occupying different ecological niches. Respiration rates and kinetic properties of citrate synthase (CS) were compared in these species in order to identify possible mechanisms of temperature adaptation. Specimens were acclimated to 5 and 15 degrees C prior to further investigations. Respiration rates were measured under normoxic conditions at 5, 10 and 15 degrees C. CS was partly purified chromatographically and influences of temperature, pH, substrate saturation and ATP-concentration on enzyme activity were examined. In both species, rising temperatures led to linearly increasing oxygen consumption, with estimated Q10 values between 3.2 and 4.2. Only I. baltica showed an effect of short term acclimation: warm adapted animals had always higher respiration rates than cold adapted ones. In I. emarginata, the acclimation temperature had no effect on oxygen consumption. Furthermore, its CS slightly indicates higher affinity to oxaloacetic acid when specimens were adapted to 15 degrees C compared to those maintained at 5 degrees C. Any effect of the experimental temperature on CS in I. baltica was negligible. The results are discussed in view of the different habitats occupied by the species compared.
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PMID:Effects of temperature on the respiration rates and the kinetics of citrate synthase in two species of Idotea (Isopoda, Crustacea). 1084 Jun 43


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