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At least 973 records · Page 54Linked to original sources
PubMed2003

Development and optimization of a method for the analysis of low-molecular-mass organic acids in plants by capillary electrophoresis with indirect UV detection.

Capillary zone electrophoresis was developed to analyze low-molecular-mass organic acids including oxalic, tartaric, formic, malic, citric, succinic, glutaric, acetic and lactic acid. The influences of some crucial parameters such as buffer concentration, pH value, surfactant concentration and separation temperature, on electrophoretic separation were investigated. Under the conditions of 15 mM phthalate containing 0.6 mM tetradecyltrimethylammonium bromide as the run buffer (pH 5.6); separation voltage -15 kV (-263.2 V/cm) and temperature 25 degrees C, a satisfactory separation of nine organic acids was accomplished within 7 min. The detection limits (S/N=3) ranged from 0.008 to 0.08 microg/ml and the quantification limits ranged from 0.01 to 0.1 microg/ml for electrokinetic injection. The method was successfully applied to analyze organic acids in different parts of Var splendens (an edible vegetable in China). The recoveries of organic acids in real samples ranged from 88 to 121%.

Acids↗
PubMed2005

Composition of quince (Cydonia oblonga Miller) seeds: phenolics, organic acids and free amino acids.

Phenolic compounds, organic acids and free amino acids of quince seeds were determined by HPLC/DAD, HPLC/UV and GC/FID, respectively. Quince seeds presented a phenolic profile composed of 3-O-caffeoylquinic, 4-O-caffeoylquinic, 5-O-caffeoylquinic and 3,5-dicaffeoylquinic acids, lucenin-2, vicenin-2, stellarin-2, isoschaftoside, schaftoside, 6-C-pentosyl-8-C-glucosyl chrysoeriol and 6-C-glucosyl-8-C-pentosyl chrysoeriol. Six identified organic acids constituted the organic acid profile of quince seeds: citric, ascorbic, malic, quinic, shikimic and fumaric acids. The free amino acid profile was composed of 21 identified free amino acids and the three most abundant were glutamic and aspartic acids and asparagine.

Acids↗
PubMed2001

Regulation of peroxisome proliferator activated receptor alpha-mediated pathways in alcohol fed cytochrome P450 2E1 deficient mice.

Fatty acids are substrates and inducers for cytochrome P450 2E1 (CYP2E1) and peroxisome proliferator activated receptor alpha (PPARalpha). Previously, we have shown that the ethanol-induced CYP2E1 expression in rat is accompanied by the inhibition of the expression of the PPARalpha gene and the reduction in polyunsaturated fatty acid content. To further analyze the effect of CYP2E1 and ethanol in PPARalpha-mediated fatty acid homeostasis, the expression of PPARalpha and retinoid x receptor alpha (RXRalpha) and their target genes was examined in ethanol fed CYP2E1 deficient mice. Our data demonstrated that the expression of PPARalpha and RXRalpha genes was activated in the livers of CYP2E1-null mice suggesting a compensatory effect for the absence of CYP2El. In addition, the expression of PPARalpha target genes, which included the liver fatty acid-binding protein, malic enzyme, and CYP4A1 genes, was induced indicating the activation of PPARalpha-mediated pathways in CYP2E1 deficient mice. Ethanol inhibited the expression of some of the PPARalpha target genes in wild-type mouse livers, and the inhibitory effect of ethanol was particularly prominent in the CYP2E1-null mice. Morphologically, centrilobular fat accumulation was detected in the ethanol fed CYP2E1-null mouse livers suggesting that inhibition of PPARalpha-mediated pathways might be responsible for the ethanol-induced fatty liver in CYP2El-null mice. In addition, the expression of CYP2E1 was not changed in the PPARalpha-null mice. These data suggest that CYP2E1 and ethanol can regulate PPARalpha-mediated fatty acid homeostasis. CYP2E1-induced lipid peroxidation might play a major role in lipid metabolism, PPARalpha only becomes important when the CYP2E1 level is low and polyunsaturated fatty acids increase.

Journal Article↗
PubMed2002

Utilization of fluorogenic assay for rapid detection of Escherichia coli in acidic fruit juice.

This study was undertaken to investigate interference by acids commonly found in fruit juice in Escherichia coli assays involving the use of 4-methylumbelliferyl-beta-D-glucuronide (MUG) as a fluorogenic substrate for enzyme reaction. Fluorescence intensity was negatively correlated (P < 0.001) with the volume of fresh citrus juice tested by the lauryl tryptose broth (LST)-MUG assay, and the permissible sample sizes were limited to 0.3 and 0.5 ml for fresh citrus juices with pHs of 3.3 and 3.9, respectively. In addition, false-negative results were visually observed under UV light when the E*Colite assay was used to test large volumes (5 to 10 ml per test) of fresh citrus juice or when the test broth used for the LST-MUG assay was supplemented with citric, malic, or tartaric acid at 2 to 4 g/liter. These results suggest that the size and pH of acidic samples should be controlled in MUG-based fluorogenic assays. The inhibitory effect on fluorescence was due to high acidity, which reduces fluorescence from 4-methylumbelliferone. Buffering improved the assays. When sodium bicarbonate was incorporated in the enrichment broth at 10 g/liter, the permissible sample sizes for fresh grapefruit juice (pH 3.1) increased from 0.3 to 1 ml for the LST-MUG (with 9.9 ml of broth) assay and from 3 to 10 ml for the E*Colite (with 99 ml of broth) assay.

Bacteriological Techniques↗
PubMed1998

Comparison of the effects of concentration, pH and anion species on astringency and sourness of organic acids.

The separate effects of concentration, pH and anion species on intensity of sourness and astringency of organic acids were evaluated. Judges rated sourness and astringency intensity of lactic, malic, tartaric and citric acid solutions at three levels of constant pH varying in normality and at three levels of constant concentration varying in pH. To assess the comparative sourness and astringency of the organic acid anions of study, binary acid solutions matched in pH and titratable acidity were also rated. As pH was decreased in equinormal solutions, both sourness and astringency increased significantly (P < 0.001). By contrast, as the normality of the equi-pH solutions was increased, only sourness demonstrated significant increases (P < 0.001) while astringency remained constant or decreased slightly. At the lowest normality tested, all solutions were more astringent than sour (P < 0.05). Although lactic acid was found to be significantly more sour than citric acid (P < 0.05), no other sourness or astringency differences among the organic acid anions were noted. This study demonstrates for the first time that astringency elicited by acids is a function of pH and not concentration or anion species, and confirms that sourness is independently influenced by concentration, pH and anion species of the acid.

Anions↗
PubMed1994

Coordinate regulation of glycolytic and lipogenic gene expression by polyunsaturated fatty acids.

Using a combination of in vivo and in vitro studies, we have investigated the impact of polyunsaturated fatty acids (PUFA) on the expression of several genes encoding proteins involved in hepatic glycolysis and lipogenesis. Meal-training rats to a high glucose diet containing 10% triolein led to a significant induction of hepatic mRNAs encoding glucokinase (GK), pyruvate kinase (PK), fatty acid synthase (FAS), malic enzyme (ME), and the S14 protein (S14), but had no effect on thyroid hormone receptor-beta 1 (TR beta 1) and c/EBP alpha gene expression. Replacing triolein with menhaden oil attenuated (by 50-90%) the induction of mRNA encoding GK, ME, PK, FAS, and S14. This effect was rapid (within hours) and for FAS and S14, directed at the transcriptional level. The mRNAs encoding TR beta 1, c/EBP alpha and beta-actin were unaffected by menhaden oil. Studies with cultured primary hepatocytes showed that C18:3,omega 3 (n-3), C18:3,omega 6 (n-6), C20:4, omega 6 (n-6), and C20:5,omega 3 (n-3) were all equally effective at suppressing the level of mRNAs encoding FAS, S14, and PK. This effect was specific for glycolytic and lipogenic enzymes, as expression of beta-actin was not affected by these fatty acids. Moreover, the fatty acids had only marginal effects on cell viability as judged by lactate dehydrogenase release. These data indicate that polyunsaturated fatty acids coordinately regulate the expression of several enzymes involved in carbohydrate and lipid metabolism. The mechanism of control does not require extrahepatic factors or fatty acid metabolism.

Animals↗
PubMedDate not supplied

Lipogenic enzyme activities in subcutaneous adipose tissue and skeletal muscle from neonatal pigs consuming maternal or formula milk.

The influence of maternal and formula milk on lipid metabolism was studied in 7-day-old pigs. Lipid content, fatty acid composition, lipogenic enzyme activities and expression of GLUT4 mRNA were determined in subcutaneous adipose tissue and skeletal muscle from pigs that were bottle-fed formula milk (F) or sow milk (SM), or were sow-reared (SR). Bottle-fed pigs were isoenergetically fed and achieved similar daily body weight gain. SR pigs have a higher (P < 0.05) body weight gain than bottle-fed pigs. Lipid content of adipose tissue was lower (P < 0.05) in F than in SM and SR pigs. In muscle, lipid content did not differ significantly between groups. In adipose tissue, acetyl-CoA-carboxylase (CBX), fatty acid synthase (FAS), malic enzyme (ME), glucose-6-phosphate-dehydrogenase (G6PDH) and lipoprotein lipase (LPL) activities and GLUT4 mRNA levels were higher (P < 0.05) in SR than in bottle-fed pigs. In muscle, ME and G6PDH activities and GLUT4 mRNA were higher (P < 0.05) in F than in SM and SR pigs; LPL was not detected. The present study indicates that lipogenic enzyme activities and GLUT4 mRNA expression are regulated differently in subcutaneous adipose tissue and skeletal muscle in the neonatal pig.

Acetyl-CoA Carboxylase↗
PubMed1980

Involvement of tyrosyl residues in the substrate binding of pigeon liver malic enzyme.

The reactions of pigeon liver malic enzyme (L-malate:NADP+ oxidoreductase (oxaloacetate-decarboxylating), EC 1.1.1.40) with tetranitromethane and N-acetylimidazole have been investigated to obtain information about the functional role of tyrosine residues in this enzyme. Incubation of the sulfhydryl-masked enzyme with tetranitromethane or N-acetylimidazole caused a time-dependent loss of all enzymatic activities of this enzyme. The absorption spectra of both the nitrated and acetylated enzyme indicated modification of tyrosine residues. The enzymatic activity of the acetylated enzyme was reversed by hydroxylamine. No amino group modification was observed. Preincubation of the enzyme with dicarboxylate substrate (or inhibitor), nucleotide coenzyme and divalent metal ions protected the enzyme against these reagents. The acetylated enzyme showed different kinetic properties from the native enzyme. The apparent Michaelis constants for malate and oxaloacetate increase by 2-5-fold. The binding between acetylated enzyme and NADPH was not abolished. These results strongly suggest the involvement of tyrosine residues in the dicarboxylic acid binding of malic enzyme.

Acetylation↗
PubMed1989

Fatty acid synthetizing enzymes in adipocytes and stromavascular fraction of hyperthyroid rat adipose tissue.

In the rat, hyperthyroidism induced from birth has been shown to increase both adipose cell recruitment and de novo lipogenesis at 6 weeks of age. Since preadipose cells are included into the stromavascular fraction (SVF) of adipose tissue, fatty acid synthetizing enzyme activities were estimated separately in adipocytes and SVF cells of adipose tissue of 6 week-old hyperthyroid rats. Fatty acid synthetase (FAS), malic enzyme (ME), glucose-6-phosphate dehydrogenase (G6PD) and 6-phosphogluconate dehydrogenase (6PGD) activities were generally increased in adipocytes and in SVF cells when compared to age-matched controls. Among the enzymes studied, ME activity displayed the highest stimulation in SVF cells and was much more stimulated in these cells than in adipocytes (214% and 73% increase, respectively, above control values, P less than 0.001). These results show that, in vivo, SVF cells and adipocytes can respond differently to an hormonal stimulation and raise the question of the role of ME in the adipose conversion.

Adipose Tissue↗
PubMed1989

Effects of cimaterol, a beta-adrenergic agonist, on lipid metabolism in rats.

Rats fed a high carbohydrate diet containing 10 or 100 ppm cimaterol for 4 weeks gained 41% to 59% less fat and 70% to 76% more protein than controls, with no major changes in either energy gain or efficiency of energy retention. Effects of cimaterol on lipid metabolism in these rats were assessed. Cimaterol stimulated lipolysis in vivo and in vitro, but failed to influence rates of de novo fatty acid synthesis in either liver or white adipose tissue. Activities of fatty acid synthetase and malic enzyme in these tissues were also unaffected by cimaterol. Cimaterol administered in vivo failed to affect lipoprotein lipase activity in white adipose tissue, but elevated enzyme activity 67% to 75% in the extensor digitorium longus muscle. Lipoprotein lipase activity in the extensor digitorum longus muscle was also elevated by 66% during a 2 hour incubation with 1 mmol/L cimaterol. We conclude that cimaterol selectively stimulates both lipolysis in white adipose tissue and lipoprotein lipase activity in skeletal muscle, to direct energy away from adipose tissue deposition toward skeletal muscle accretion.

Adipose Tissue↗
PubMed2002

A soy protein diet alters hepatic lipid metabolism gene expression and reduces serum lipids and renal fibrogenic cytokines in rats with chronic nephrotic syndrome.

Nephrotic syndrome (NS) is characterized by the presence of proteinuria and hyperlipidemia. However, ingestion of soy protein has a hypolipidemic effect. The present study was designed to determine whether the ingestion of a 20% soy protein diet regulates the expression of hepatic sterol regulatory element binding protein (SREBP)-1, fatty acid synthase (FAS), malic enzyme, beta-hydroxy-beta-methylglutaryl-CoA (HMG-CoA) reductase (r) and synthase (s), and LDL receptor (r), and to assess whether soy protein improves lipid and renal abnormalities in rats with chronic NS. Male Wistar rats were injected with vehicle or with puromycin aminonucleoside to induce NS and were fed either 20% casein or soy protein diets for 64 d. NS rats fed 20% soy protein had improved creatinine clearance and reduced proteinuria, hypercholesterolemia, hypertriglyceridemia, as well as VLDL-triglycerides and LDL cholesterol compared with NS rats fed the 20% casein diet. In addition, the soy protein diet decreased the incidence of glomerular sclerosis, and proinflammatory cytokines in kidney. Ingestion of the soy protein diet by control rats reduced the gene expression of SREBP-1, malic enzyme, FAS and increased HMG-CoAr, HMG-CoAs and LDLr. However, NS rats fed either casein or soy protein diets had low insulin concentrations with reductions in SREBP-1, FAS and malic enzyme expression compared with control rats fed the casein diet. NS rats fed the soy diet also had lower HMG-CoAr and LDLr mRNA levels than NS rats fed casein. In conclusion, the beneficial effects of soy protein on lipid metabolism are modulated in part by SREBP-1. However, in NS rats, the benefit may be through a direct effect of this protein on kidney rather than mediated by changes in expression of hepatic lipid metabolism genes.

Animals↗
PubMed2002

Effect of plant oils and organic acids on rumen fermentation in vitro.

We determined the effect of plant oils (rapeseed, sunflower, linseed) and organic acids (aspartic and malic) on the fermentation of diet consisting of hay, barley and sugar beet molasses. Rumen fluid was collected from two sheep (Slovak Merino) fed with the same diet twice daily. Mixed rumen microorganisms were incubated in fermentation fluid, which contained rumen fluid and Mc Dougall's buffer. All supplemented diets significantly increased pH, molar proportion of propionate, and numerically decreased methane production. Lactate production was also decreased significantly (except with malate). Incorporation of plant oils into aspartate- and malate-treated incubations negated the decrease of butyrate, lactate and the increase of pH and ammonia with malate treatment, as well as in vitro dry matter digestibility and pH with aspartate treatment. The effect of combined additives on methane production and molar proportion of propionate was lower compared with additives supplemented separately. Combination of additives had no additive effect on rumen fermentation. All additives decreased total protozoan counts in rumen fluid.

Animal Feed↗
PubMed2006

Simultaneous determination of carbohydrates, carboxylic acids, alcohols, and metals in foods by high-performance liquid chromatography inductively coupled plasma atomic emission spectrometry.

The applicability of the HPLC-ICP-AES coupling for the simultaneous determination of carbohydrates, carboxylic acids, alcohols, and metals in a single chromatographic run has been demonstrated in the present work. Five saccharides, glucose, fructose, sucrose, sorbitol, and lactose; five carboxylic acids, citric, tartaric, malic, lactic, and acetic; and three alcohols, glycerol, ethanol, and methanol, have been determined. A H+ cation exchange column has been used to separate these compounds. The chromatograms have been obtained by monitoring the carbon emission signal at 193.09 nm. The results obtained by HPLC-ICP-AES have been compared against those found with conventional detection systems (i.e., refractive index, UV, and photodyode array detectors). The HPLC-ICP-AES method has shown the following features: (i) organic compounds and metals can be simultaneously determined; (ii) the detection method is universal; (iii) for nonvolatile organic compounds, a complete calibration line can be obtained from a single injection; and (iv) it provides absolute limits of detection similar to or lower than those found with conventional detection systems (i.e., on the order of several tens of nanograms of organic compound). The methodology has been validated through the analysis of food samples such as juices, isotonic beverages, wines, and a certified nonfat milk powder sample.

Alcohols↗
PubMed2001

New approaches for fabrication of microfluidic capillary electrophoresis devices with on-chip conductivity detection.

In practice, microfluidic systems are based on the principles of capillary electrophoresis (CE), for a large part due to the simplicity of electroosmotic pumping. In this contribution, a universal conductivity detector is presented that allows detection of charged species down to the microM level. Additionally, powderblasting is presented as a novel technique for direct etching of microfluidic networks. This method allows creation of features down to 50 microm with a total processing time (design to device) of less than one day. The performance of powderblasted devices with integrated conductivity detection is illustrated by the separation of lithium, sodium, and potassium ions and that of fumaric, malic, and citric acid.

Acids↗
PubMed1980

Gas chromatographic determination of extracellular metabolites produced by baker's yeast during glucose-induced acidification.

Gas chromatographic separation of metabolites extruded during the medium acidification by resting baker's yeast supplied with glucose is described. Silylation with bis(trimethylsilyl)trifluoroacetamide and trimethylchlorosilane and a direct chromatography on Chromosorb G-AW-DMCS with 2.5% SE-52 (lactic, pyruvic, succinic, glyceric, fumaric, malic), polyols (glycerol, arabinitol) and sugars (glucose). The yeast was found to extrude glycerol, lactic, malic, and succinic acid.

Chromatography, Gas↗
PubMed1980

Extrusion of metabolites from baker's yeast during glucose-induced acidification.

Extrusion of metabolites (glycerol, lactic, malic, and succinic acid) during the medium acidification caused by resting baker's yeast supplied with 200 mM glucose was studied under aerobic and anaerobic conditions and in the absence and presence of 14 mM KCl. The maximum levels of glycerol and of the sum of acids (about 13 and 8 mM, respectively) were attained anaerobically; aerobiosis reduced the levels by 40-50% and the presence of K+ ions by another 10-20%. The time courses of glucose consumption and medium acidification were similar aerobically and anaerobically. The glucose consumption curves exhibited a short plateau about 2 min after glucose addition, caused probably by a rapid osmotic equilibration of glucose across the cell mambrane. Metabolite extrusion indicates that at high glucose concentrations the alcohol dehydrogenase reaction is supplemented by other reactions aiding in the maintenance of a balanced NAD+/NADH ratio in the cells.

Anaerobiosis↗
PubMed2001

A fruit-specific phospho enolpyruvate carboxylase is related to rapid growth of tomato fruit.

Malic and citric acids accumulate in cherry tomato (Lycopersicon esculentum Mill.) fruit during the period of rapid growth, from the end of cell division to the onset of ripening. The involvement of phospho enolpyruvate carboxylase (PEPCase, EC 4.1.1.31) in organic acid accumulation and tomato fruit development was investigated. Two PEPCases, named LYCes;Ppc1 and LYCes;Ppc2 and mapped to chromosomes 12 and 7, respectively, were shown to be differentially expressed during tomato fruit development. LYCes;Ppc1 mRNA was present in all fruit tissues and in all other plant organs examined. In contrast, LYCes;Ppc2 was strongly and specifically expressed in fruit from the end of cell division to ripening. No LYCes;Ppc2 expression was detected by northern blot in other plant tissues. In fruit, the increase in LYCes;Ppc2 mRNA was closely followed by an increase in fruit PEPCase protein and activity, and was coincident with the increased accumulation of malate and citrate during the initial period of rapid growth rate, from 8 to 20 days post anthesis. Localization of LYCes;Ppc2 mRNA in young tomato fruit by in situ hybridization revealed that LYCes;Ppc2 is preferentially expressed in large cells of the pericarp and in enlarging cells of the gel surrounding the seeds. Examination of the kinetic and regulatory properties of the PEPCases of growing and ripening fruit further showed that PEPCase in growing fruit is less sensitive to low pH and malate inhibition, indicating a high phosphorylation state and/or the presence of a PEPCase isoform with these characteristics. Taken together, these results indicate that in developing tomato fruit PEPCase is probably important in permitting the synthesis of organic acids to provide the turgor pressure necessary for cell expansion.

Chromosome Mapping↗
PubMed1985

Diurnal variations of lipogenic enzymes, their substrate and effector levels, and lipogenesis from tritiated water in rat liver.

The activities of glucose-6-phosphate dehydrogenase, malic enzyme, fatty acid synthetase and acetyl-CoA carboxylase (extracted with or without phosphatase inhibitor) in rat liver did not vary significantly during 24 h. The hepatic levels of glucose 6-phosphate and malate increased coordinately 3-6 h after the beginning (1900 h) of food intake and were high until morning, whereas the levels of acetyl-CoA and citrate peaked at 1900 h and then decreased. However, it is remarkable that the in vivo incorporation of 3H from tritiated water into fatty acids in liver increased with the level of malonyl-CoA after food intake. Comparing the substrate and effector levels with the Km and Ka values for the enzymes, the levels of acetyl-CoA, malonyl-CoA and citrate appear to limit the enzyme activities. It is suggested that, after food intake, the physiological activity of acetyl-CoA carboxylase was increased with the substrate increase and/or with the catalytic activation with citrate, and consequently, the fatty acid synthetase activity was also increased, whereas the enzyme activities measured under optimum conditions were not.

Acetyl-CoA Carboxylase↗