Activities Of Citrate Cleavage Enzyme Research Articles

Effects of Pantethine Supplementation to Diets with Different Energy Cereals on Hepatic Lipogenesis of Laying Hens

Effects on dietary pantethine supplementation on hepatic lipid accumulation and on the activities of lipogenic-related enzymes in the liver were studied in Single Comb White Leghorn laying hens fed isocaloric and isonitrogenous diets containing corn or barley as the carbohydrate source. Addition of 200 ppm pantethine to the corn-soy (CS) basal diet significantly reduced abdominal fat weight, liver triglyceride, as well as total cholesterol and 17β-estradiol concentrations in the plasma. Activities of citrate cleavage enzyme (EC 4.1.3.8; CCE) and fatty acid synthetase (FAS) in the liver were significantly reduced when the CS basal diet was supplemented with pantethine, but the activities of nicotinamide adenine dinucleotide phosphate-malate dehydrogenase (EC 1.1.1.40; NADP-MDH) and glucose-6-phosphate dehydrogenase (EC 1.1.1.49; G6PDH), were not significantly affected. However, liver triglyceride, total cholesterol, and 17β-estradiol concentrations in plasma as well as the activities of CCE, FAS, and NADP-MDH in liver were significantly lower in laying hens fed the barley-soy (BS) basal diet than in those fed the CS basal diet. Pantethine supplementation to the BS diet failed to show any significant effect on liver triglyceride content and on the hepatic activities of lipogenic-related enzymes. There were no significant differences in liver weight, rate of egg production, and egg weight among dietary treatments, these results suggest that dietary pantethine is effective in reducing the accumulation of liver and abdominal fat in laying hens fed a CS diet.

Characterization of Plasma Hormone Levels and Lipogenic Enzyme Activity in Chickens Divergently Selected for Oxygen Consumption

The bases for differences in growth and metabolism of lines previously selected for divergence in O2 consumption in comparison to a randombred control population were studied. Body weights, carcass fat, plasma growth hormone (GH), triiodothyronine (T3), thyroxine (T4), malic enzyme, and citrate cleavage enzyme activities were determined. The early growth of the low O2 birds was greater than the high O2 birds, whereas the growth rate of the control population was intermediate to, but not statistically different from, the two O2 lines. Six-week body weights did not differ between the lines. Percent fat of the high O2 birds was less than the other two lines at 1 and 2 weeks of age but greater than the low O2 birds at 3 weeks of age. Percent fat did not differ between the lines at 6 weeks. Plasma T4 levels differed between the lines only at Day 1, when the control population exhibited greater T4 levels than the O2 lines. Plasma T3 levels were lower in the high O2 chicks in comparison to only the control chicks at 0, 1, and 2 weeks of age. No line differences in T3 levels were detected at 3 or 6 weeks. From 1 to 3 weeks, GH levels were greater in the low O2 birds than the high O2, while the control birds had GH levels intermediate to the O2 lines. By 6 weeks, the O2 lines had similar GH levels, but these levels were lower than those of the controls. No consistent line differences in malic enzyme or citrate cleavage enzyme activities were observed.

Effect of Increasing Dietary Energy on Hepatic Lipogenesis in Growing Chicks: II. Increasing Energy by Fat or Protein Supplementation.

The effect of increasing the energy content of the diet through supplementation of various levels of fat or protein on hepatic lipogenesis and activities of associated enzymes of liver was examined in force-fed growing chicks.Hepatic lipogenesis was significantly decreased as the dietary metabolizable energy level was increased through supplementation of fat or protein.The activity of nicotinamide adenine dinucleotide phosphate-malate dehydrogenase (NADP-MDH) (EC 1.1.1.40) in liver was higher (P<.01) in chicks fed diets containing the lowest energy level. The activity of citrate cleavage enzyme (EC 4.1.3.8) in liver was significantly depressed as the dietary metabolizable energy level increased through supplementation of fat, whereas increasing the dietary metabolizable energy level through protein supplementation resulted in a significant increase in citrate cleavage enzyme activity in liver.Nonesterified fatty acid concentration in serum was significantly increased as the dietary metabolizable energy level was increased through supplementation of fat.

A Metabolic Comparison of Cysteine and Methionine Supplements in the Diet of a Rat

Adult male Long-Evans rats (250–300 g) were fed diets containing 15% of casein not supplemented with amino acids, supplemented with 0.505% cysteine or supplemented with 0.620% methionine for a period of 17 days. Rats fed the diets supplemented with cysteine had an increased incorporation of the 14C-radioactivity from [U-14C]alanine into liver glycogen and a decreased incorporation from [U-14C]acetate into fatty acids. Pyruvate carboxylase activity was slightly increased and citrate cleavage enzyme activity decreased in the livers of those rats fed the diets supplemented with cysteine. Rats fed diets supplemented with methionine had a decreased liver phosphoenolpyruvate carboxykinase activity. Based on these data it appears that rats fed diets supplemented with cysteine adapt metabolically to store energy as glycogen, while those fed diets supplemented with methionine tend to store energy as lipid.

Chronic Hyperinsulinemia in the Fetal Rhesus Monkey: Effects on Hepatic Enzymes Active in Lipogenesis and Carbohydrate Metabolism

Hyperinsulinemia was produced in fetal rhesus monkeys for 21 days in the last third of gestation by subcutaneous pork insulin injected at 19 U a day. Plasma insulin concentrations in treated fetuses (N = 4) were 3525 microU/ml. There was no difference in paired pre- and post-treatment fetal plasma glucose concentration. Activity of the hepatic enzymes that promote glucose utilization (glucokinase and hexokinase) and glycolysis (phosphofructokinase, pyruvate kinase, and pyruvate dehydrogenase) was unaffected. Similarly, glycogen metabolism enzymes (active and inactive synthase and phosphorylase) were unaltered. Two gluconeogenic enzymes (PEPCK and glucose-6-phosphatase) were diminished in the treated group compared with controls. Fetal hyperinsulinemia enhanced lipogenic and NADPH-producing enzyme activities, as evidenced by a twofold increase in fatty acid synthase and in citrate cleavage enzyme activity. Malic enzyme was absent. Hyperinsulinemia with euglycemia (1) increases the activity of enzymes that participate in lipogenesis, (2) decreases some of those controlling gluconeogenesis, and (3) has no effect on the enzymes of glycolysis.

Effects of chronic hyperinsulinaemia on hepatic enzymes involved in lipogenesis and carbohydrate metabolism in the young rat.

Chronic (6 days) hyperinsulinaemia in young rats produced lower blood glucose concentrations and augmented body- and liver-weight gain. The insulin-treated rats had increased hepatic activities of citrate-cleavage enzyme, 'malic' enzyme and high-substrate (6.6 mM-phosphoenolpyruvate) pyruvate kinase, and decreased glucose 6-phosphatase. There were no changes in activities of phosphoenolpyruvate carboxykinase, phosphofructokinase, low-substrate (1.3 mM-phosphoenolpyruvate) pyruvate kinase, glucokinase and hexokinase.

Fatty Acid Synthesis in Testes of Fat-deficient and Fat-supplemented Rats

Fatty acid synthesis was studied in testes of rats fed a fat-free or fat-supplemented diet. Testes of fat-deficient rats incorporated nearly twice as much intratesticularly injected [1-14C]acetate into total fatty acids (primarily into palmitic acid) as did supplemented rats. To determine the mechanism for the increased synthesis, the activities of the following enzymes were determined in the cytoplasmic fraction of testicular homogenates: fatty acid synthetase, acetyl CoA carboxylase [EC 6.4.1.2], citrate-cleavage [EC 4.1.3.8], malic [EC 1.1.1.38], and the glucose-l-phosphate dehydrogenase [EC 1.1.1.49]: 6-phosphogluconate dehydrogenase pair [EC 1.1.1.44]. Although the activity of fatty acid synthetase did increase in livers from fat-deficient rats, no change was observed in corresponding testes. No difference between the two groups could be demonstrated in testicular activity of citrate-cleavage enzyme, malic enzyme, or the glucose-6-phosphate dehydrogenase: 6-phosphogluconate dehydrogenase pair. However, the activity of cytoplasmic acetyl CoA carboxylase in testes of rats fed the fat-deficient diet was 1.4 times higher than the activity in testes of rats fed the supplemented diet. Fat deficiency did not affect the specific activity of the testicular microsomal elongation system, assayed by incubation with 14C-malonyl CoA. The concentration of unesterified fatty acids was lower in testes of the fat-deficient compared to supplemented rats, indicating that decreased inhibition of acetyl CoA carboxylase in the fat-deficient rats testes might have been responsible for the observed increased de novo synthesis of palmitic acid.

Influence of (—)-Hydroxycitrate on Lipogenesis in Chickens and Rats

The influence of (-)-hydroxycitrate on in vitro rates of fatty acid synthesis in chicken and rat liver and in rat adipose tissue was investigated. Following acute and chronic administration of (-)-hydroxycitrate to chickens and rats, changes in rates of fatty acid synthesis in vivo and in lipogenic enzyme activities were also determined. Addition of 1 mM (-)-hydroxycitrate to a buffer containing 10 mM glucose and liver slices from chickens or rats depressed the rate of 3H2O incorporation into fatty acids. Acute administration of (-)-hydroxycitrate to chickens and rats also depressed in vivo rates of fatty acid synthesis in the livers of these species. Chickens appeared to be more sensitive to the inhibitory effects of (-)-hydroxycitrate than did rats. (-)-Hydroxycitrate was incorporated into the diets fed to the chickens and rats. Hepatic citrate cleavage enzyme activities were increased several fold in livers of chickens and rats fed (-)-hydroxycitrate. However, the rates of fatty acid synthesis in chicken and rat livers were depressed when expressed per g liver. Livers of chickens fed (-)-hydroxycitrate for 14 days were enlarged. Dietary (-)-hydroxycitrate did not depress rates of fatty acid synthesis per liver in these birds. Consumption of (-)-hydroxycitrate did not alter liver weight in rats. In vivo rates of fatty acid synthesis in rat adipose tissue were not influenced by consumption of a diet containing 52.6 nmoles (-)-hydroxycitrate/kg diet. Plasma triglyceride levels were increased two-fold in chickens, but unchanged in rats, fed (-)-hydroxycitrate for 2 to 3 weeks. There are species-specific as well as organ-specific responses to (-)-hydroxycitrate.

Effect of Glycerol on Lipogenic Enzyme Activities and on Fatty Acid Synthesis in the Rat and Chicken

The influence of glycerol on the rates of fatty acid snythesis in liver slices from rats and chickens in pieces of adipose tissue from rats was first studied. Then the effect of dietary glycerol on lipid metabolism in rats and cheickens was examined. Media containing 3 or 10 mM glycerol depressed the rate of glucose conversion to fatty acids in rat liver slices. However, media containing up to 25 mM glycerol did not influence the rate of fatty acid synthesis in chick liver slices. The inhibitory action of glycerol in rat liver slices might occur at the level of glucose (or glycogen) conversion to pyruvate because glycerol did not inhibit pyruvate or acetate conversion to fatty acids. Rats and chickens were fed glycerol containing diets for either 3 days or 3 weeks. Feeding diets containing 20.5 parts glycerol (22% of dietary energy) to rats or chickens did not influence the growth rate of the animals. However, substitution of 42.2 parts glycerol (43% of dietary energy) for glucose in the diet significantly depressed food intake and growth rate in both rats and chickens. The activities of citrate cleavage enzyme, fatty acid synthetase and malic enzyme in livers of rats fed the glycerol-containing diets were dramatically increased. However, this stimulation of enzyme activity occurred without a concomitant increase in the in vivo rate of fatty acid synthesis in the rat liver. In the chicken, unlike the rat, dietary glycerol did not stimulate but instead decreased hepatic malic enzyme and fatty acid synthetase activities. No significant differences in adipose tissue lipogenic enzyme activities or in the rates of fatty acid synthesis were observed in rats fed glycerol-containing diets. The lipogenic response to glycerol feeding depends on the species as well as the organ.

The Effect of Dietary Vanadium on Fatty Acid and Cholesterol Synthesis and Turnover in the Chick

Day-old male, broiler type chicks were used to study the effect of 100 ppm dietary vanadium on fatty acid and cholesterol synthesis and turnover in vivo. After feeding the experimental diets for 4 weeks body weight and liver weight of chicks fed 100 ppm vanadium were significantly less than those of the control chicks and liver total lipid and cholesterol tended to be slightly higher than the levels of the control chicks. [1-14C] Acetate was administered intravenously and the specific activities of plasma and liver total lipid, cholesterol and fatty acid were determined at 0.25, 0.50, 1.0, 4.0, 8.0 and 15.0 hours after the injection. Plasma total lipid and cholesterol were significantly higher than the levels in the control chicks. The rate of incorporation of [1-14C]acetate into plasma and liver total lipid, cholesterol and fatty acid was higher in chicks fed vanadium than the control group at any of the time being tested after the injection. There was a significant increase in the hepatic citrate cleavage enzyme activity among chicks fed 100 ppm vanadium, whereas, there was no significant change in acetate thiokinase activity. Turnover rate of plasma total lipid and fatty acid in vanadium fed chicks was lower than the control. The turnover rate of plasma cholesterol determined by administering [4-14C]cholesterol and periodically measuring the specific activity of plasma cholesterol was higher in chicks fed vanadium than in those fed the basal diet.

An analysis of the relationships among obesity, plasma insulin and hepatic lipogenic enzymes in "viable yellow obese" mice (Avy/a).

The development of obesity, hyperinsulinemia and six hepatic lipogenic enzymes in Avy/a mice were compared to that in a/a mice. Correlation between body weight, liver weight, plasma insulin concentration and activities of hepatic enzymes was analyzed. In the Avy/a mice, body weight, liver weight and plasma insulin level increased steadily as the mice aged. In the a/a mice, the change of these three parameters was much slower. Plasma insulin concentration in a/a mice did not increase until eight months of age. Compared with a/a mice, Avy/a mice had higher 6-phosphogluconate dehydrogenase and fatty acid synthetase activities at two months of age; lower citrate cleavage enzyme, glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities at three months of age; lower citrate cleavage enzyme and glucose-6-phosphate dehydrogenase and higher acetyl CoA carboxylase activities at five months of age; and higher malic enzyme, citrate cleavage enzyme and 6-phosphogluconate dehydrogenase activities at eight months of age. There were significant correlations between plasma insulin level and body weight and between plasma insulin level and the activities of malic enzyme and citrate cleavage enzyme in Avy/a mice. The correlation between body weight and malic enzyme and citrate cleavage enzyme activities disappeared after the analysis was adjusted for plasma insulin level.

Studies in vitro of lipogenesis in rat testicular tissue

Testicular tissue was shown to contain the full complement of enzymes required for de novo synthesis of fatty acids. The enzymes capable of snythesizing palmitic acid from citrate, acetate, or acetyl CoA were found to be present in the soluble (cytoplasmic) fraction. These included fatty acid synthetase, acetyl CoA carboxylase, citrate-cleavage enzyme, malic enzyme, glucose-6-phosphate dehydrogenase, and 6-phosphogluconate dehydrogenase. Optimal conditions for assaying activities of fatty acid synthetase and acetyl CoA carboxylase in the soluble fraction from rat testes were established, and the activities of these two enzymes were determined to be 0.54 +/- 0.1 and 0.030 +/- 0.002 (nmoles of substrate incorporated into fatty acid per min per mg of soluble fraction protein), respectively. The activities of citrate-cleavage enzyme, malic enzyme, and the glucose-6-phosphate dehydrogenase/6-phosphogluconate dehydrogenase pair were also measured. The activities were 6.0 +/- 0.7, 34.9 +/- 4.2, and 29.9 +/- 9.3 nmoles/min/mg, respectively.

High glucose concentration and phosphoenolpyruvate carboxykinase activity in human and rat fetal liver cultures.

In cultures of human and rat fetal liver, phosphoenolpyruvate carboxykinase activity increases during the first 24 hr of culturing. This increase can be suppressed by adding cycloheximide to the culture medium or by adding a high glucose concentration. This, however, applies only to human fetal liver and to fetal liver from rats obtained just before term. In younger rat fetal liver, glucose, on the contrary, increases the activity of phosphoenolpyruvate carboxykinase. A high glucose concentration in the medium also leads to higher citrate cleavage enzyme activity and to lower alpha-glycerolphosphate dehydrogenase (cytoplasmic) activity in rat fetal liver cultures.

Lipogenesis and Glyceride Synthesis in the Rat: Response to Diet and Exercise

The responses of hepatic and adipose tissue malic enzyme (ME), citrate cleavage enzyme (CCE), glucose-6-phosphate dehydrogenase (G6PD), and glyceride synthetase (GS) to exercise training and exhaustive exercies and the potential of a high fat or high carbohydrate diet to modify these responses were studied in male Carworth rats. Characteristic elevation and depression of ME, CCE, and G6PD were decreased in skeletal muscle, liver, and adipose tissues of high carbohydrate-fed rats. A significant two-way diet-training interaction was indicated for hepatic ME and G6PD. This interaction resulted from an apparent training modulation of ME and C6PD responses to the high fat and high carbohydrate diets. Adipose tissue G6PD was significantly decreased by training. Exhaustive exercise performed immediately prior to sacrifice did not significantly alter ME or CCE activities in either liver or adipose tissues, but decreased adipose tissue G6PD in untrained rats. Exhaustion was also associated with decreased GS activity in muscle and liver. Physical training was associated with a significant increase in GS in muscle and adipose tissues. In contrast to glyceride synthesis, no increase in adipose tissue lipogenic potential was noted in response to training, indicating that the physically trianed rat may have an enhanced ability to store but not synthesize fatty acids.

Fatty acid synthesis de novo in human adipose tissue.

1. Homogenates of subcutaneous adipose tissue from obese subjects contained sufficient citrate cleavage enzyme (EC 4.1.3.8: ATP—citrate oxaloacetate lyase), acetyl-CoA carboxylase (EC 6.4.1.2: acetyl-CoA—carbon dioxide ligase) and fatty acid synthetase to account for the rates of fatty acid synthesis reported in the literature for intact tissues in vitro. 2. The distribution of label in fatty acids after incubations of adipose tissue with [1-14C]acetate was consistent with fatty acid synthesis de novo, not chain elongation. 3. The activities of citrate cleavage enzyme and fatty acid synthetase in subcutaneous adipose tissue were reduced by short periods of starvation. 4. These findings indicate that human adipose tissue is capable of fatty acid synthesis de novo and that two of the enzymes concerned adapt to starvation.

Effect of ethanol consumption on lipid metabolism in the Buffalo rat.

The substitution of 20% alcohol for drinking water of Buffalo rats maintained on an adequate diet demonstrated significant decreases in glucose-6-phosphate dehydrogenase, formiminotransferase, malic and citrate cleavage enzyme activities. This is in contrast to the Charles River and other strains of rats. Liver studies using labeled glucose and acetate indicated that the Buffalo rat is capable of synthesizing approximately twice as much lipid from glucose compared with the Charles River rat. The results suggest that the Buffalo rat has a sensitivity to alcohol related to certain aspects of lipid metabolism not seen in the Charles River rat or other strains.

Influence of background genome on enzymatic characteristics of yellow (A v -, A vy -) mice.

Identification of the fundamental polypeptide difference between yellow (A(y)/-, A(vy)/-) and non-yellow mice is important for biomedical research because of the influence of the yellow genotype on normal and neoplastic growth and obesity. The complexity of the "yellow mouse syndrome" makes attainment of this objective dependent on the separation of those pleiotropic enzyme differences which are secondary, and depend on the background genome, from those which are primary, and depend primarily on the agouti locus genotype.-Four of nine hepatic enzyme activities assayed simultaneously differed between eight-week-old yellow (A(y)/-, A(vy)/-) and non-yellow (A/-, a/a) male inbred and F(1) hybrid mice. Among these four, only cytoplasmic malic enzyme activity was elevated in all yellow mice, as compared with the non-yellow sibs, regardless of background genome. Glucokinase, serine dehydratase, and tyrosine alpha-ketoglutarate transaminase activities were also changed in yellow mice, but these alterations depended on the background genome.-The ratio of malic enzyme activity to citrate-cleavage enzyme activity, possibly related to the altered fat metabolism of yellow mice, was influenced by background genome as well as by the yellow genotype.--Significant deviations of enzyme activities from mid-parent values among F(1) hybrids were associated with particular background genomes; the number of such deviations was larger among yellow mice than among non-yellows and this difference was greater among C3H F(1) hybrids than among C57BL/6 F(1) hybrids.

The effect of temperature and length of exposure on liver composition and hepatic lipogenic enzyme activity in the immature male chick ( gallus domesticus)

1. 1. A time-course study of the effects of temperature on liver composition and hepatic lipogenic enzyme acitivity was carried out using immature male chicks maintained at 17 and 30°C. 2. 2. The main effects of maintaining birds at the lower temperature appeared to be associated with a marked increase in liver size. 3. 3. Temperature and length of exposure had a significant effect on liver composition. 4. 4. Temperature had no significant effect on the specific activities of citrate-cleavage enzyme, “malic” enzyme or isocitrate dehydrogenase although there was a substantial, if non-significant, increase in “malic” enzyme activity in birds maintained at 17°C. 5. 5. Temperature differences in the specific activity of hepatic citrate-cleavage enzyme could not be correlated with NADPH production from either “malic” enzyme or isocitrate dehydrogenase.

Estimations of rates of synthesis and degradation of several rat mammary gland enzymes from changes in enzyme activities.

Based upon rates of decrease in the activities of citrate cleavage enzyme (EC 4.1.3.7), malic enzyme (EC 1.1.1.40), fatty acid synthetase, UDPglucose pyrophosphorylase (EC 2.7.7.9), UDPglucose 4-epimerase (EC 5.1.3.3), and glucose-6-phosphate dehydrogenase (EC 1.1.1.49) in rat mammary glands after adrenalectomy–ovariectomy on the 11th day of lactation, the half-lives of the enzymes were estimated to be 28, 31, 28, 50, 20, and 24 h, respectively. The half-life estimates for UDPglucose pyrophosphorylase and glucose-6-phosphate dehydrogenase compared favorably with previous estimates of 35 and 20 h, respectively, obtained in rats 5 days postpartum utilizing specific immunological techniques. In a second experiment, increases in the activities of enzymes in adrenalectomized, lactating rats after initiation of cortisol therapy were investigated. Rats were adrenalectomized on the 5th day of lactation and cortisol therapy was started 5 days later. The estimated half-lives for citrate cleavage enzyme, malic enzyme, fatty acid synthetase, UDPglucose pyrophosphorylase, UDPglucose 4-epimerase, the A protein of the lactose synthetase complex, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase (EC 1.1.1.44), and hexokinase (EC 2.7.1.1) were, respectively, 84, 60, 92, 76, 170, 102, 79, 88, and 81 h.

Hormonal regulation of rat mammary gland enzyme activities and metabolite patterns.

Activities of nine enzymes and the levels of 15 metabolites were determined in mammary glands from normal (N) and adrenalectomized–ovariectomized (AO) rats in midlactation. Mammary gland weights and mammary DNA did not change between day 11 and day 19 of lactation in N animals and were not affected appreciably by AO. Four days after AO the activities of citrate cleavage enzyme, malic enzyme, UDPglucose pyrophosphorylase, the A protein of the lactose synthetase complex, and glucose-6-phosphate dehydrogenase were decreased to 24, 59, 53, 52, and 56% of day 11 N. These same enzymes require cortisol therapy to increase in activity after adrenalectomy on the 5th day of lactation. Activities of phosphoglucomutase, 6-phosphogluconate dehydrogenase, fructose-1,6-diphosphate aldolase, and isocitrate dehydrogenase were not affected by AO. These enzymatic changes are discussed in relation to systems regulating milk synthesis. Mammary glucose levels increased 1.9-fold in AO animals. Levels of triose phosphate, α-glycerol phosphate, and aspartate in AO animals were decreased to 52, 49, and 62% of N. The proportion of high-energy phosphate bonds to total adenine nucleotides was not affected by AO. Ratios of [free NADP]/[free NADPH2] were not significantly affected by AO or stage of lactation. Metabolite patterns are discussed in relation to changes in enzyme activities and in vitro tracer data.