Enzymes of the tricarboxylic acid cycle in Obeliscoides cuniculi (Nematoda; Trichostrongylidae) during parasitic development

The specific activities of the enzymes of the tricarboxylic acid cycle; citrate synthase, aconitase, isocitrate dehydrogenase, succinate dehydrogenase, fumarase, and malate dehydrogenase, were determined in early fifth-stage, young and mature adult Obeliscoides cuniculi, the rabbit stomach worm. ∝-Ketoglutarate dehydrogenase activity could not be determined in any fraction. Fumarate reductase activity was found only in the mitochondrial fraction while all other enzymes, including an NADP-dependent malic enzyme were localized in the cytoplasm. Glutamate dehydrogenase, acid and alkaline phosphatase activities were also recorded. High levels of those enzymes acting in the “reversed” direction, i.e. MDH and fumarase relative to the enzymes of the “forward” direction, i.e. citrate synthase, aconitase and isocitrate dehydrogenase suggests that under anaerobic conditions a modified tricarboxylic acid cycle can operate. Some variations in specific activities were apparent as the worms matured but no qualitative differences were observed.     

Relationship between glycerol-3-phosphate dehydrogenase,fatty acid synthase and fatty acid binding proteins in developing human placenta

The activities of the enzymes glycerol-3-phosphate dehydrogenase and fatty acid synthase are inhibited by palmitoyl-coenzyme A and oleate. The two isoforms of fatty acid binding proteins (PI 6.9 and PI 5.4) enhance the activities of glycerol-3-phosphate dehydrogenase and fatty acid synthase in the absence of palmitoyl-coenzyme A or oleate and also protect them against palmitoyl-coenzyme A or oleate inhibition. Levels of fatty acid binding proteins, the activities of the enzymes fatty acid synthase and glycerol-3-phosphate dehydrogenase increase with gestation showing a peak at term. However, the activity of fatty acid synthase showed the same trend up to the 30th week of gestation and then declined slightly at term. With the advancement of pregnancy when more lipids are required for the developing placenta, fatty acid binding proteins supply more fatty acids and glycerol-3-phosphate for the synthesis of lipids. Thus a correlation exists between glycerol-3-phosphate dehydrogenase, fatty acid synthase and fatty acid binding proteins in developing human placenta.     

Regulation of the dicarboxylic acid part of the citric acid cycle in Bacillus subtilis.

The regulation of alpha-ketogluterate dehydrogenase, succinate dehydrogenase, fumarase, malate dehydrogenase, and malic enzyme has been studied in Bacillus subitilis. The levels of these enzymes increase rapidly during late exponential phase in a complex medium and are maximal 1 to 2 h after the onset of sporulation. Regulation of enzyme synthesis has been studied in the wild type and different citric acid cycle mutants by adding various metabolites to the growth medium. Alpha-ketoglutarate dehydrogenase is induced by glutamate or alpha-ketoglutarate; succinate dehydrogenase is repressed by malate; and fumarase and malic enzyme are induced by fumarate and malate, respectively. The addition of glucose leads to repression of the citric acid cycle enzymes whereas the level of malic enzyme is unaffected. Studies on the control of enzyme activities in vitro have shown that alpha-ketoglutarate dehydrogenase and succinate dehydrogenase are inhibited by oxalacetate. Enzyme activities are also influenced by the energy level, expressed as the energy charge of the adenylate pool. Isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, succinate dehydrogenase, and malic enzyme are inhibited at high energy charge values, whereas malate dehydrogenase is inhibited at low energy charge. A survey of the regulation of the citric acid cycle in B.subtilis, based on the present work and previously reported results, is presented and discussed.     

Effect of dietary alpha-linolenic acid on the activity and gene expression of hepatic fatty acid oxidation enzymes

The activities of hepatic fatty acid oxidation enzymes in rats fed linseed and perilla oils rich in alpha-linolenic acid (alpha-18:3) were compared with those in the animals fed safflower oil rich in linoleic acid (18:2) and saturated fats (coconut or palm oil). Mitochondrial and peroxisomal palmitoyl-CoA (16:0-CoA) oxidation rates in the liver homogenates were significantly higher in rats fed linseed and perilla oils than in those fed saturated fats and safflower oil. The fatty oxidation rates increased as dietary levels of alpha-18:3 increased. Dietary alpha-18:3 also increased the activity of fatty acid oxidation enzymes except for 3-hydroxyacyl-CoA dehydrogenase. Unexpectedly, dietary alpha-18:3 caused great reduction in the activity of 3-hydroxyacyl-CoA dehydrogenase measured with short- and medium-chain substrates but not with long-chain substrate. Dietary alpha-18:3 significantly increased the mRNA levels of hepatic fatty acid oxidation enzymes including carnitine palmitoyltransferase I and II, mitochondrial trifunctional protein, acyl-CoA oxidase, peroxisomal bifunctional protein, mitochondrial and peroxisomal 3-ketoacyl-CoA thiolases, 2, 4-dienoyl-CoA reductase and delta3, delta2-enoyl-CoA isomerase. Fish oil rich in very long-chain n-3 fatty acids caused similar changes in hepatic fatty acid oxidation. Regarding the substrate specificity of beta-oxidation pathway, mitochondrial and peroxisomal beta-oxidation rate of alpha-18:3-CoA, relative to 16:0- and 18:2-CoAs, was higher irrespective of the substrate/albumin ratios in the assay mixture or dietary fat sources. The substrate specificity of carnitine palmitoyltransferase I appeared to be responsible for the differential mitochondrial oxidation rates of these acyl-CoA substrates. Dietary fats rich in alpha-18:3-CoA relative to safflower oil did not affect the hepatic activity of fatty acid synthase and glucose 6-phosphate dehydrogenase. It was suggested that both substrate specificities and alterations in the activities of the enzymes in beta-oxidation pathway play a significant role in the regulation of the serum lipid concentrations in rats fed alpha-18:3.     

Inhibition of key enzymes of carbohydrate metabolism in regenerating mouse liver by ascorbic acid.

The effect of ascorbic acid on the key enzymes of carbohydrate metabolism e.g. hexokinases, phosphofructokinase, pyruvate kinase, lactate dehydrogenase, glucose-6-phosphate dehydrogenase and malic enzyme was determined in regenerating mouse liver. All the enzymes showed a significant increase in the activity during regeneration. Ascorbic acid reduced the activities of the enzymes in regenerating liver. A decrease in liver weight in ascorbic acid treated animals may be correlated with its effect on these enzymes as glycolytic pathway is the main source of energy required by the dividing cells.     

Tricarboxylic acid cycle enzymes of a pseudophyllid cestode Penetrocephalus ganapatii

Studies on the tricarboxylic acid cycle (TCA cycle) enzymes of Penetrocephalus ganapatii reveal that the TCA cycle is only partially operative, as some of the enzymes at the start of the cycle viz. citrate synthase, aconitase and isocitrate dehydrogenase are found to be low in their activities. The high activities of malate dehydrogenase and fumarase, showing affinity towards a reverse direction, indicate that the TCA cycle operates in the reverse direction resulting in the formation of fumarate. The low succinate dehydrogenase/fumarate reductase ratio suggests that ATP generation may occur at site I of the respiratory chain during the reduction of fumarate into succinate.     

Effect of DL-alpha-lipoic acid on mitochondrial enzymes in aged rats.

Mitochondrial dysfunction appears to contribute to some of the loss of function accompanying ageing. Mitochondria from aged tissue use oxygen inefficiently impairing ATP synthesis and results in increased oxidant production. A high flux of oxidants not only damages mitochondria, but other important cell biomolecules as well. In the present investigation, the levels of lipid peroxidation, oxidized glutathione, non-enzymatic antioxidants and the activities of mitochondrial enzymes were measured in liver and kidney mitochondria of young and aged rats before and after lipoic acid supplementation. In both liver and kidney increase in the levels of mitochondrial lipid peroxidation and oxidized glutathione and decrease in the levels of antioxidants and the activities of mitochondrial enzymes were observed in aged rats. DL-alpha-lipoic acid supplemented aged rats showed a decrease in the levels of lipid peroxidation and oxidized glutathione and increase in the levels of reduced glutathione, vitamins C and E and the activities of mitochondrial enzymes like isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, succinate dehydrogenase, NADH-dehydrogenase and cytochrome-c-oxidase. Thus, lipoic acid reverses the age-associated decline in endogenous low molecular weight antioxidants and mitochondrial enzymes and, therefore, may lower the increased risk of oxidative damage that occurs during ageing. From our results it can be concluded that lipoic acid supplementation enhances the activities of mitochondrial enzymes and antioxidant status and thereby protects mitochondria from ageing.     

The tricarboxylic acid cycle of Helicobacter pylori.

The composition and properties of the tricarboxylic acid cycle of the microaerophilic human pathogen Helicobacter pylori were investigated in situ and in cell extracts using [1H]- and [13C]-NMR spectroscopy and spectrophotometry. NMR spectroscopy assays enabled highly specific measurements of some enzyme activities, previously not possible using spectrophotometry, in in situ studies with H. pylori, thus providing the first accurate picture of the complete tricarboxylic acid cycle of the bacterium. The presence, cellular location and kinetic parameters of citrate synthase, aconitase, isocitrate dehydrogenase, alpha-ketoglutarate oxidase, fumarate reductase, fumarase, malate dehydrogenase, and malate synthase activities in H. pylori are described. The absence of other enzyme activities of the cycle, including alpha-ketoglutarate dehydrogenase, succinyl-CoA synthetase, and succinate dehydrogenase also are shown. The H. pylori tricarboxylic acid cycle appears to be a noncyclic, branched pathway, characteristic of anaerobic metabolism, directed towards the production of succinate in the reductive dicarboxylic acid branch and alpha-ketoglutarate in the oxidative tricarboxylic acid branch. Both branches were metabolically linked by the presence of alpha-ketoglutarate oxidase activity. Under the growth conditions employed, H. pylori did not possess an operational glyoxylate bypass, owing to the absence of isocitrate lyase activity; nor a gamma-aminobutyrate shunt, owing to the absence of both gamma-aminobutyrate transaminase and succinic semialdehyde dehydrogenase activities. The catalytic and regulatory properties of the H. pylori tricarboxylic acid cycle enzymes are discussed by comparing their amino acid sequences with those of other, more extensively studied enzymes.     

Tricarboxylic acid cycle enzymes following thiamine deficiency

Thiamine (Vitamin B1) deficiency (TD) leads to memory deficits and neurological disease in animals and humans. The thiamine-dependent enzymes of the tricarboxylic acid (TCA) cycle are reduced following TD and in the brains of patients that died from multiple neurodegenerative diseases. Whether reductions in thiamine or thiamine-dependent enzymes leads to changes in all TCA cycle enzymes has never been tested. In the current studies, the pyruvate dehydrogenase complex (PDHC) and all of enzymes of the TCA cycle were measured in the brains of TD mice. Non-thiamine-dependent enzymes such as succinate dehydrogenase (SDH), succinate thiokinase (STH) and malate dehydrogenase (MDH) were altered as much or more than thiamine-dependent enzymes such as the alpha-ketoglutarate dehydrogenase complex (KGDHC) (-21.5%) and PDHC (-10.5%). Succinate dehydrogenase (SDH) activity decreased by 27% and succinate thiokinase (STH) decreased by 24%. The reductions in these other enzymes may result from oxidative stress because of TD or because these other enzymes of the TCA cycle are part of a metabolon that respond as a group of enzymes. The results suggest that other TCA cycle enzymes should be measured in brains from patients that died from neurological disease in which thiamine-dependent enzymes are known to be reduced. The diminished activities of multiple TCA cycle enzymes may be important in our understanding of how metabolic lesions alter brain function in neurodegenerative disorders.     

Fatty acid degradation in Caulobacter crescentus.

Fatty acid degradation was investigated in Caulobacter crescentus, a bacterium that exhibits membrane-mediated differentiation events. Two strains of C. crescentus were shown to utilize oleic acid as sole carbon source. Five enzymes of the fatty acid beta-oxidation pathway, acyl-coenzyme A (CoA) synthase, crotonase, thiolase, beta-hydroxyacyl-CoA dehydrogenase, and acyl-CoA dehydrogenase, were identified. The activities of these enzymes were significantly higher in C. crescentus than the fully induced levels observed in Escherichia coli. Growth in glucose or glucose plus oleic acid decreased fatty acid uptake and lowered the specific activity of the enzymes involved in beta-oxidation by 2- to 3-fold, in contrast to the 50-fold glucose repression found in E. coli. The mild glucose repression of the acyl-CoA synthase was reversed by exogenous dibutyryl cyclic AMP. Acyl-CoA synthase activity was shown to be the same in oleic acid-grown cells and in cells grown in the presence of succinate, a carbon source not affected by catabolite repression. Thus, fatty acid degradation by the beta-oxidation pathway is constitutive in C. crescentus and is only mildly affected by growth in the presence of glucose. Tn5 insertion mutants unable to form colonies when oleic acid was the sole carbon source were isolated. However, these mutants efficiently transported fatty acids and had beta-oxidation enzyme levels comparable with that of the wild type. Our inability to obtain fatty acid degradation mutants after a wide search, coupled with the high constitutive levels of the beta-oxidation enzymes, suggest that fatty acid turnover, as has proven to be the case fatty acid biosynthesis, might play an essential role in membrane biogenesis and cell cycle events in C. crescentus.     

The effects of estradiol administration of the hepatic activities of some enzymes of carbohydrate, amino acid and lipid metabolism in the immature pullet.

Two experiments were performed to examine the effects of intramuscular estradiol administration on the hepatic specific activities of some enzymes of lipid, carbohydrate and amino acid metabolism in the immature fowl. Estradiol increased the specific activities of the hepatic lipogenic enzymes, ATP citrate lyase and malate dehydrogenase (decarboxylating) (NADP), but had no effects on the activities of the glycolytic, gluconeogenic and amino acid metabolising enzymes except for pyruvate kinase and glutamate dehydrogenase which were reduced in activity in both experiments. The results indicate that the estrogen-induced increase in hepatic lipid biosynthesis is due to a specific effect on lipid metabolism and not to a general increase in liver metabolism.     

The influence of lipoic acid on adriamycin induced nephrotoxicity in rats

Adriamycin, which is widely used in the treatment of various neoplastic conditions, exerts toxic effects in several organs. Adriamycin nephrotoxicity has been recently documented in a variety of animal species. The present study was designed to investigate the effect of lipoic acid on the nephrotoxic potential of adriamycin. The study was carried out with adult male albino rats of Wistar strain. Test animals were divided into four groups of six rats each as follows: Group I (control) received only normal saline throughout the course of the experiment. Group II (ADR) received intravenous injections of adriamycin through the tail vein (1 mg kg^–1 body wt day^–1) once a week for a period of 12 weeks. Group III (LA) received lipoic acid (35 mg kg^–1 body wt day^–1) intraperitoneally once a week for a period of 12 weeks. Group IV (ADR + LA) received a single injection of lipoic acid intraperitoneally 24 h prior to the administration of adriamycin through the tail vein once a week for a period of 12 weeks. Intravenous injections of adriamycin resulted in decreased activities of the glycolytic enzymes; hexokinase, phosphoglucoisomerase, aldolase and lactate dehydrogenase in the rat renal tissue. The gluconeogenic enzymes; glucose-6-phosphatase and fructose-1,6-diphosphatase, showed a decline in their activities on adriamycin administration. The transmembrane enzymes namely the Na⁺,K⁺-ATPase, Ca²⁺-ATPase, Mg²⁺-ATPase and the brush-border enzyme alkaline phosphatase also showed a decrease in their activities. This decrease in the activities of ATPases and alkaline phosphatase suggests basolateral and brush-border membrane damage. Decreased activities of the TCA cycle enzymes isocitrate dehydrogenase, succinate dehydrogenase and malate dehydrogenase, suggest a loss in mitochondrial function and integrity. Nephrotoxicity was evident from the increased excretions of N-acetyl--D-glucosaminidase and -glutamyl transferase in the urine of adriamycin administered rats. These biochemical disturbances were effectively counteracted on pretreatment with lipoic acid, which brought about an increase in the activities of glycolytic enzymes, ATPases and the TCA cycle enzymes. On the other hand, the gluconeogenic enzymes showed a further decrease in their activities on lipoic acid pretreatment. LA pretreatment also restored the activities of the urinary enzymes to normal. These observations shed light on the nephroprotective action of lipoic acid rendered against experimental aminoglycoside toxicity.     

Branched-chain amino acid oxidation by isolated rat tissue preparations

Branched-chain amino acid transaminase activity, branched-chain α-keto acid dehydrogenase activity, and leucine oxidation were measured in homogenates and slices of several rat tissues. Transaminase activity was highest in heart, while dehydrogenase activity was highest in liver. Leucine oxidation in isolated tissues may be limited by either transaminase or dehydrogenase activity depending upon the relative activities of these two enzymes in the tissue. The results suggest that, as the load of branched-chain amino acids increases, the liver may become an increasingly important site for the degradation of branched-chain α-keto acids.     

Induction of the branched-chain 2-oxo acid dehydrogenase complex in 3T3-L1 adipocytes during differentiation.

The activities of 2-oxo acid dehydrogenase complexes were measured during hormone-mediated differentiation of 3T3-L1 preadipocytes into adipocytes. Specific activity of leucine-activated branched-chain 2-oxo acid dehydrogenase complex increased approx. 10-fold in 3T3-L1 adipocytes compared with 3T3-L1 preadipocytes. In contrast, specific activity of the 2-oxoglutarate dehydrogenase complex increased by only 3-fold in 3T3-L1 adipocytes. The three catalytic component enzymes of the branched-chain 2-oxo acid dehydrogenase complex and the pyruvate dehydrogenase complex showed concomitant increases in their specific activities. A close similarity in kinetics of induction of the branched-chain 2-oxo acid dehydrogenase complex and the pyruvate dehydrogenase complex in 3T3-L1 adipocytes suggests that a common mechanism may be involved in hormone-dependent increases in the activities of the catalytic components of these two complexes in 3T3-L1 adipocytes during differentiation.     

Effect of 24-hour starvation on amino acid pool composition and enzyme activities of rat brown adipose tissue

The effect of 24-hr starvation on the amino acid pool composition and its concentration ratios with respect to blood and plasma as well as the activities of alanine, aspartate and branched chain amino acid transaminases, glutamate dehydrogenase, glutamine synthetase and adenylate deaminase have been studied in rat brown adipose tissue. Starvation induced a considerable decrease of pool amino acid concentration. Alanine and taurine were the amino acids in which the decrease was more marked. Small changes were observed in the activities of the enzymes studied, with decreases only in glutamate dehydrogenase and adenylate deaminase. These changes agree with a decrease in amino acid utilization in this tissue induced by starvation.     

The effect of phenolic compounds on the activity of respiratory chain enzymes and on respiration and phosphorylation activities of potato tuber mitochondria

The effect of derivatives of benzoic and cinnamic acids, quereetin,p-benzoquinone, and 2,5-dimethylbenzoquinone on oxygen consumption mitoehondrial suspensions and on the activity of some respiratory chain enzymes was studied. Benzoquinone and 2,5-dimethylbenzoquinone highly significantly inhibited the respiration and phosphorylation rates and malate- and succinate dehydrogenase activities. Chlorogenic acid, similarly as the quinones, very significantly inhibited the activities of the studied dehydrogenases but did not affect cytochrome oxidase. Oxygen consumption by intact mitochondria was not inhibited, only the oxidativo phosphorylation was significantly uncoupled. Quereetin significantly enhanced dehydrogenase activities and completely inhibited cytochrome oxidase activity. The respiration and phosphorylation activities of the mitochondria were significantly inhibited by quereetin. The effect of the other phenolic compounds studied on respiration and phosphorylation activities was not significant. Succinate dehydrogenase activity was the most affected enzyme among the respiratory chain enzymes. It was significantly inhibited by all the above phenolic compounds at 1^-4M or 5 10^-5M concentrations with the exception of gallic acid.     

Ascorbic acid and alpha-tocopherol as potent modulators on arsenic induced toxicity in mitochondria

Arsenic exists ubiquitously in our environment and various forms of arsenic circulate in air, water, soil and living organisms. Since arsenic compounds have shown to exert their toxicity chiefly by generating reactive oxygen species, we have evaluated the effect of antioxidants ascorbic acid and alpha-tocopherol on lipid peroxidation, antioxidants and mitochondrial enzymes in liver and kidney of arsenic exposed rats. A significant increase in the level of lipid peroxidation and decrease in the levels of antioxidants and in the activities of mitochondrial enzymes were observed in arsenic intoxicated rats. Co-administration of arsenic treated rats with ascorbic acid and alpha-tocopherol showed significant reduction in the level of lipid peroxidation and elevation in the levels of ascorbic acid, alpha-tocopherol, glutathione and total sulfhydryls and in the activities of isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, succinate dehydrogenase, NADH-dehydrogenase and cytochrome c oxidase. From our results, we conclude that ascorbic acid and alpha-tocopherol alleviate arsenic- induced alterations in mitochondria.     

Changes in the activities of enzymes involved in amino acid metabolism during the senescence of detached wheat leaves

The activities of several enzymes related to amino acid metabolism were investigated in senescing detached wheat leaves ( Triticum aestivum L. cv. Diplomat) in light and darkness and after kinetin treatment. Glutamine synthetase and glutamate synthase activities rapidly declined in darkness. In light, the decline of glutamate synthase activity was retarded, while the activity of glutamine synthetase remained high and even increased transitorily. Kinetin treatment counteracted the decline of the activities of both enzymes. The activity of glutamate dehydrogenase markedly increased during senescence, particularly in light, and kinetin treatment lowered its activity. The activities of glutamate-oxaloacetate and glutamate-pyruvate amino-transferases and of NADP-dependent isocitrate dehydrogenase also increased in detached wheat leaves in light. Kinetin treatment prevented the rise of these enzyme activities. In darkness, the activities of glutamate-oxaloacetate aminotransferase and NADP-dependent isocitrate dehydrogenase decreased slowly while the decline of glutamate-pyruvate aminotransferase activity was more rapid. The activity of NAD-dependent malate dehydrogenase decreased both in light and, more rapidly, in darkness. The pattern of changes of the enzyme activities provides an explanation for the amino acid transformations and the flow of amino nitrogen into transport metabolites in senescing leaves.     

Grape seed proanthocyanidins ameliorates isoproterenol-induced myocardial injury in rats by stabilizing mitochondrial and lysosomal enzymes: an in vivo study

This study was designed to examine the effects of grape seed proanthocyanidins (GSP) against myocardial injury (MI) induced by isoproterenol (ISO), in a rat model. Induction of rats with ISO (85 mg/kg body weight, subcutaneously) for 2 days resulted in a significant decrease in the activities of heart mitochondrial enzymes (isocitrate dehydrogenase, succinate dehydrogenase, malate dehydrogenase and alpha-ketoglutarate dehydrogenase) and respiratory chain enzymes (NADH dehydrogenase and cytochrome c oxidase). The activities of lysosomal enzymes (alpha-d-glucuronidase, alpha-d-N-acetylglucosaminidase, cathepsin-D, acid phosphatases and alpha-d-galactosidase) were increased significantly in the heart and serum of ISO-induced rats. The prior administration of GSP for 6 days a week for 5 weeks significantly increased the activities of mitochondrial and respiratory chain enzymes and significantly decreased the activities of lysosomal enzymes in the heart tissues of ISO-induced rats, which proves the stress stabilizing action of GSP. Oral administration of grape seed proanthocyanidins alone (50, 100 and 150 mg/kg) to normal rats did not show any significant effect in all the parameters studied. These biochemical functional alterations were supported by the macroscopic enzyme mapping assay of ischemic myocardium. Thus, this study shows that 100 and 150 mg/kg of GSP gives protection against ISO-induced MI and demonstrates that GSP has a significant effect in the protection of heart.