Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.3.3.1 (citrate synthase)
 4,488 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

This study investigates the effects of physiological increments in plasma thyroxine (T4) at three levels of biological organization in thyroid-intact and thyroidectomized captive western fence lizards, Sceloporus occidentalis. Two doses of T4-loaded pellets elevated plasma T4 in thyroid-intact lizards from 4.8 +/- 0.47 to 10.7 +/- 2.25 and 20.4 +/- 5.77 ng/ml (mean +/- SE). Surgical thyroidectomy reduced T4 to 1.8 +/- 0.23 ng/ml, and subsequent T4 pellet implantation raised T4 to 14.8 +/- 4.30 ng/ml. Minimal resting metabolic rate (= standard metabolic rate; SMR), a common organismal metric of thyroid perturbation, was reduced 31% (P less than 0.0001) by thyroidectomy and was restored by T4 replacement but was not stimulated by T4 supplementation in thyroid-intact lizards. In T4-replaced, thyroidectomized lizards, SMR was significantly correlated with plasma T4 (r2 = 0.626, P = 0.003, n = 11). At the organ level, liver mass was not changed by any treatment; heart mass was decreased by thyroid deficiency and restored by T4 replacement. At the molecular level, citrate synthase activity was significantly reduced by thyroidectomy and was returned to control levels by T4 replacement in liver and skeletal muscle (gastrocnemius) but was not changed in cardiac muscle. Citrate synthase was not affected in any tissue by T4 supplementation in thyroid-intact lizards. Pyruvate kinase activity was not affected by any of the treatments in any of the tissues. Cytosolic alpha-glycerophosphate dehydrogenase was significantly reduced in liver by all treatments and in skeletal muscle by T4 replacement after thyroidectomy. These results indicate that SMR and cardiac muscle mass in lizards are dependent on normal thyroid function and are expressed maximally in euthyroid animals. The stimulatory effect of T4 on SMR in thyroid-intact lizards, which has been reported previously by several investigators, is a nonphysiological response to pharmacological T4 levels, at least in these captive lizards. Molecular responses are tissue and enzyme dependent and cannot be generalized. Pellet implantation is an effective means of inducing physiological increments in plasma T4 and should replace previously used injection protocols. This new method can be used in capture-recapture experiments involving field-active lizards.
 ...
PMID:Thyroid regulation of resting metabolic rate and intermediary metabolic enzymes in a lizard (Sceloporus occidentalis). 229 23

This study was undertaken to examine the effects of thyroid hormonal deficiency on (1) standard (SMR) and maximal (VO2max) rates of O2 consumption, (2) tissue glycolytic and oxidative capacities and (3) submaximal locomotory endurance in a lizard (Dipsosaurus dorsalis). Surgical thyroidectomy induced hypothyroidism in all animals as determined by levels of plasma thyroxine. Hypothyroid lizards had lower levels of SMR (-48%), VO2max (-16%) and citrate synthase activity in liver, heart and skeletal muscle compared to controls. There was a correlated decrease in locomotory endurance in thyroid-deficient animals. Pyruvate kinase activity (an index of glycolytic capacity) in all tissues, and myofibrillar ATPase activity (an index of contractile velocity) in white iliofibularis muscle, showed no significant changes in thyroid-deficient animals. Thyroid hormones appear to be important in ultimately establishing an animal's capacity for locomotory endurance. These findings suggest a new selective context for understanding the evolution of thyroid function.
 ...
PMID:Reduced aerobic capacity and locomotory endurance in thyroid-deficient lizards. 673 62

Eastern red-spotted newts are ectotherms, aquatic as adults, and active year-round, breeding even during winter under ice. Earlier research, with field-captured newts, showed a correlation between seasonal changes in the activity of some muscle metabolic enzymes and in the behavior of the newts in a thermal gradient. This study was undertaken to further characterize acclimatory responses in the newts in a more controlled laboratory environment. Newts were obtained during fall, and maintained at 15 degrees C with 12:12 LD for 4 weeks for SMR (at 8 and 26 degrees C) and temperature preference experiments. Subsequently, half the newts were exposed to summer conditions (26 degrees C, 14:10 LD) and half to winter conditions (8 degrees C, 10:14 LD). After 12 weeks, SMR and temperature preference experiments were repeated, and enzyme assays for cytochrome c oxidase (CCO), citrate synthase (CS), and lactate dehydrogenase (LDH) were performed on muscle tissue homogenates, also at 8 and 26 degrees C. Newts changed all three parameters in the laboratory. SMRs were highest in winter-acclimated newts and lowest in summer-acclimated newts, whereas temperature preference was lowest in winter-acclimated newts and highest in summer-acclimated newts. Finally, CCO activity was completely compensated in winter-acclimated newts, CS activity was partially compensated, and LDH activity was not seasonally sensitive. These results indicate a connection or relationship between changes in seasonal environmental conditions, and some aspects of the muscle biochemistry, SMR, and thermoregulatory behavior of these ectotherms.
 ...
PMID:Phenotypic flexibility and thermoregulatory behavior in the eastern red-spotted newt (Notophthalmus viridescens viridescens). 2018 89

Highly active animals require a high aerobic capacity (i.e., a high maximum metabolic rate [MMR]) to sustain such activity, and it has been speculated that a greater capacity for aerobic performance is reflected in larger organs, which serve as energy processors but are also expensive to maintain and which increase the minimal cost of living (i.e., the basal or standard metabolic rate [SMR]). In this study, we assessed the extent of intraspecific variation in metabolic rate within a group of brown trout (Salmo trutta L.) and tested whether the observed variation in residual (body-mass-corrected) SMR, MMR, and absolute aerobic scope could be explained by variations in the residual size (mass) of metabolically active internal organs. Residual SMR was found to correlate positively with residual MMR, indicating a link between these two metabolic parameters, but no relationship between organ mass and metabolic rate was found for liver, heart, spleen, intestine, or stomach. Instead, activity in the liver of two aerobic mitochondrial enzymes, cytochrome c oxidase and, to a lesser extent, citrate synthase, was found to correlate with whole-animal metabolic rate, indicating that causes for intraspecific variation in the metabolic rate of fish can be found at a lower organizational level than organ size.
 ...
PMID:Intraspecific variation in aerobic metabolic rate of fish: relations with organ size and enzyme activity in brown trout. 2309 62

Intraspecific variation in metabolic rate of fish can be pronounced and have been linked to various fitness-related behavioural and physiological traits, but the underlying causes for this variation have received far less attention than the consequences of it. In the present study we investigated whether European eels (Anguilla anguilla) displayed temporal repeatability of body-mass-corrected (residual) metabolic rate over a two-month period and if variations in organ mass and enzyme activity between individual fish could be the cause for the observed variation in metabolic rate. Both standard metabolic rate (SMR; Pearson's r=0.743) and routine metabolic rate (RMR; r=0.496) were repeatable over the two-month period. Repeatability of RMR is an interesting finding as it indicates that the level of spontaneous activity in respirometer-confined fish is not random. Cumulative organ mass (liver, heart, spleen and intestine; mean 1.6% total body mass) was found to explain 38% of the variation in SMR (r=0.613) with the liver (one of the metabolically most active organs) being the driver for the correlation between organ mass and metabolic rate. No relationships were found for either liver citrate synthase or cytochrome oxidase activity and metabolic rate in the European eels. Reasons for, and contributions to, the observed variation in metabolic rate are discussed.
 ...
PMID:Temporal repeatability of metabolic rate and the effect of organ mass and enzyme activity on metabolism in European eel (Anguilla anguilla). 2338 12