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PubMed2005

In the aging housefly aconitase is the only citric acid cycle enzyme to decline significantly.

The main objective of this study was to determine if the activities of the mitochondrial citric acid cycle enzymes are altered during the normal aging process. Flight muscle mitochondria of houseflies of different ages were used as a model system because of their apparent age-related decline in bioenergetic efficiency, evident as a failure of flying ability. The maximal activities of each of the citric acid cycle enzymes were determined in preparations of mitochondria from flies of relatively young, middle, and old age. Aconitase was the only enzyme exhibiting altered activity during aging. The maximal activity of aconitase from old flies was decreased by 44% compared to that from young flies while the other citric acid cycle enzymes showed no change in activity with age. It is suggested that the selective age-related decrease in aconitase activity is likely to contribute to a decline in the efficiency of mitochondrial bioenergetics, as well as result in secondary effects associated with accumulation of citrate and redox-active iron.

Aconitate Hydratase↗
PubMed2001

Selectivity in citric acid production by Yarrowia lipolytica.

This experimental study reports about production selectivity in the fermentation of glucose to citric acid by Yarrowia lipolytica as a function of substrate concentration. Batch runs featuring biomass growth and one or two citric acid production phases were carried out in a 15-l stirred tank fermentor. The presented results demonstrate that working at high initial substrate concentration in the production phase is beneficial both in terms of a higher production rate of citric acid, the desired metabolite (reaching 0.077 h(-1)) and of a higher utilization degree of the employed carbon source (yield up to 0.384 g(c.a.)/g(glucose)). The production rate of isocitric acid, the major undesired metabolite, was found to be practically constant over the tested initial substrate concentration range.

Journal Article↗
PubMed1997

Clinical and microbiological effects of subgingival antimicrobial irrigation with citric acid as evaluated by an enzyme immunoassay and culture analysis.

The purpose of the present study was to compare an enzyme immunoassay with culture samples from untreated and non-surgically treated periodontal pockets and to assess the clinical and microbiological effects of citric acid irrigation as a supplement to scaling and root planing. The enzyme immunoassay used in this study is a chairside diagnostic tool aimed at identifying the presence of P. gingivalis, P. intermedia, and A. actinomycetemcomitans. Six sites with pocket depths > or = 6 mm in each of 16 patients were monitored for 24 weeks using clinical and microbiological parameters. In two out of the six sites, scaling and root planing was supplemented with subgingival citric acid irrigation of the pocket after completion of the mechanical treatment. The sensitivity of the immunoassay in relation to culture was calculated to 85.5% and the specificity to 90.2%. The immunoassay corresponded to a detection level of 10(4) as estimated by culture. Sites treated with a combination of scaling and irrigation with citric acid demonstrated a similar healing pattern as sites treated with scaling and root planing alone. The profile of the marker bacteria was almost parallel for the two groups. The results of this investigation thus indicated that the immunoassay can be used as a screening tool for selected periodontal pathogens and that adjunctive irrigation with citric acid has no measurable clinical or microbiological effects.

Adult↗
PubMed1975

Calcium oxalate and the von Kossa method with reference to the influence of citric acid.

Crystals of calcium oxalate in pathological material and artificially precipitated in the absence or presence of citric acid in gelatin models were examined by polarized light and treated with silver nitrate under a variety of conditions. It was found that the intensity of the staining reaction was largely proportional to the strength of the silver solution, and was enhanced in in vitro studies by the presence of citric acid. Staining was also influenced by the crystal form, which was itself related to the absence or presence of citric acid.

Animals↗
PubMed2000

Biosynthesis of citric acid by Yarrowia lipolytica repeat-batch culture on ethanol.

After analysis of batch culture and identification of the ways for prolongation of citric acid active synthesis by yeast, repeat-batch (RB) cultivation was suggested. Yarrowia lipolytica strain RB cultivation was studied and optimal conditions for cultivation selected. It was shown that when applying RB cultivation, better results were obtained than for batch cultivation. The activity of the culture remained stable after cultivation for more than 700 h. Comparative analysis of enzyme activities confirmed the regularity of the effect described, as the activity of practically of all the enzymes participating in ethanol oxidation and citric acid biosynthesis remained stable over time during RB cultivation. Advantages of RB cultivation for the production of citric acid by yeast are discussed.

Citric Acid↗
PubMed1991

Cigarette smoke-induced changes in guinea-pig airway responsiveness to histamine and citric acid.

The effect of 50 min cigarette smoke exposure on airway responsiveness to the bronchoconstrictor and tussive effects of histamine and citric acid has been examined in guinea-pigs. Intravenous histamine increased intratracheal pressure (ITP) in anaesthetized guinea-pigs and the dose-response curve was significantly (P less than 0.05) steeper in cigarette smoke- than in air-exposed animals. ED50 values were 11.4 nmol kg-1 (7.4-16.8, 95% confidence interval) and 42.5 nmol kg-1 (28.8-61.4, 95% confidence interval), respectively (P less than 0.05) in smoke- and air-exposed guinea-pigs indicating an enhanced reactivity. However, the sensitivity to intravenous histamine was not changed by the cigarette smoke exposure, and the maximum increase in intratracheal pressure was the same as in control animals (air: 247 +/- 21%, n = 4; smoke: 223 +/- 18%, n = 7). The cigarette smoke-induced hyperresponsiveness to intravenous histamine was not altered by pretreatment with nebulized lidocaine (0.20 M), ipratropium bromide (0.30 mM) or cromoglycate (0.06 M), suggesting that a neural reflex is unlikely to be involved in the development of hyperresponsiveness. Conscious, smoke-exposed guinea-pigs had a significantly (P less than 0.001) reduced responsiveness to citric acid (0.40 M) and cigarette smoke. Both cough and bronchoconstriction were suppressed for about 1 h, but unchanged 24 h after exposure. The hyporesponsiveness to citric acid was inhibited by atropine (1.4 mumol kg-1 i.p.) and may therefore, at least in part, be due to increased airway secretions. The present data demonstrate that inhalation of cigarette smoke may alter guinea-pig airway responsiveness to tussive and bronchoconstrictor stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2006

Influence of citric acid amendments on the availability of weathered PCBs to plant and earthworm species.

A series of small and large pot trials were conducted to assess the phytoextraction potential of several plant species for weathered polychlorinated biphenyls (PCBs) in soil (105 microg/g Arochlor 1268). In addition, the effect of citric acid on PCB bioavailability to both plants and earthworms was assessed. Under small pot conditions (one plant, 400 g soil), three cucurbits (Cucurbita pepo ssp pepo [zucchini] and ssp ovifera [nonzucchini summer squash], Cucumis sativus, cucumber) accumulated up to 270 microg PCB/g in the roots and 14 microg/g in the stems, resulting in 0.10% contaminant removal from soil. Periodic 1 mM subsurface amendments of citric acid increased the stem and leaf PCB concentration by 330 and 600%, respectively, and resulted in up to a 65% increase in the total amount of contaminant removed from soil. Although citric acid at 10 mM more than doubled the amount of PCB desorbed in abiotic batch slurries, contaminant accumulation by two earthworm species (Eisenia foetida and Lumbricus terrestris) was unaffected by citric acid at 1 and 10 mM and ranged from 11-15 microg/g. Two large pot trials were conducted in which cucurbits (C. pepo ssp pepo and ssp ovifera, C. sativus) and white lupin (Lupinus albus) were grown in 70 kg of PCB-contaminated soil White lupin was the poorest accumulator of PCBs, with approximately 20 microg/g in the roots and 1 microg/g in the stems. Both C. pepo ssp ovifera (summer squash) and C. sativus (cucumber) accumulated approximately 65-100 microg/g in the roots and 6-10 microg/g in the stems. C. pepo ssp pepo (zucchini) accumulated significantly greater levels of PCB than all other species, with 430 microg/g in the roots and 22 microg/g in the stems. The mechanism by which C. pepo spp pepo extracts and translocates weathered PCBs is unknown, but confirms earlier findings on the phytoextraction of other weathered persistent organic pollutants such as chlordane, p,p'-DDE, and polycyclic aromatic hydrocarbons.

Animals↗
PubMed2006

Citric acid cycle in the hyperthermophilic archaeon Pyrobaculum islandicum grown autotrophically, heterotrophically, and mixotrophically with acetate.

The hyperthermophilic archaeon Pyrobaculum islandicum uses the citric acid cycle in the oxidative and reductive directions for heterotrophic and autotrophic growth, respectively, but the control of carbon flow is poorly understood. P. islandicum was grown at 95 degrees C autotrophically, heterotrophically, and mixotrophically with acetate, H2, and small amounts of yeast extract and with thiosulfate as the terminal electron acceptor. The autotrophic growth rates and maximum concentrations of cells were significantly lower than those in other media. The growth rates on H2 and 0.001% yeast extract with and without 0.05% acetate were the same, but the maximum concentration of cells was fourfold higher with acetate. There was no growth with acetate if 0.001% yeast extract was not present, and addition of H2 to acetate-containing medium greatly increased the growth rates and maximum concentrations of cells. P. islandicum cultures assimilated 14C-labeled acetate in the presence of H2 and yeast extract with an efficiency of 55%. The activities of 11 of 19 enzymes involved in the central metabolism of P. islandicum were regulated under the three different growth conditions. Pyruvate synthase and acetate:coenzyme A (CoA) ligase (ADP-forming) activities were detected only in heterotrophically grown cultures. Citrate synthase activity decreased in autotrophic and acetate-containing cultures compared to the activity in heterotrophic cultures. Acetylated citrate lyase, acetate:CoA ligase (AMP forming), and phosphoenolpyruvate carboxylase activities increased in autotrophic and acetate-containing cultures. Citrate lyase activity was higher than ATP citrate synthase activity in autotrophic cultures. These data suggest that citrate lyase and AMP-forming acetate:CoA ligase, but not ATP citrate synthase, work opposite citrate synthase to control the direction of carbon flow in the citric acid cycle.

Acetates↗
PubMed1993

Lack of importance of the superior laryngeal nerves in citric acid cough in humans.

The relative importance of laryngeal afferents in the cough reflex in humans is unknown. This study was designed to investigate the importance of superior laryngeal nerve afferents in the cough reflex induced by inhaled nebulized citric acid in awake humans. Nine healthy volunteers had their cough thresholds to inhaled nebulized citric acid measured after superior laryngeal nerve conduction blockade and after a sham nerve block. Of the nine subjects, four showed no change in cough threshold after superior laryngeal nerve anesthesia, three showed increased cough threshold after nerve block compared with no block, and two showed decreased cough threshold after nerve block. The geometric means of the cough thresholds for the nerve block vs. sham block tests were 16 +/- 13 (SD) and 15 +/- 8% citric acid, respectively. There was no statistically significant difference (Wilcoxon signed-rank test) between the cough thresholds with and without superior laryngeal nerve block (P > 0.05). We conclude that, in the awake human, superior laryngeal nerve afferents do not play a necessary role in initiation of citric acid-induced cough.

Administration, Inhalation↗
PubMed1990

Importance of inspiratory flow rate in the cough response to citric acid inhalation in normal subjects.

1. The cough response to inhalation of citric acid is produced mainly by irritation of the larynx and trachea. Variations in the inspiratory flow rate might lead to changes in deposition of the drug, and consequently in the cough threshold. 2. We have studied the effect of three different inspiratory flow rates in 11 normal, non-smoking subjects (nine males, aged 23-39 years), who inhaled nebulized citric acid (2.5-640 mg/l). The test finished when a cough was produced at each inhalation (cough threshold) or the maximum concentration was reached. 3. The inspiratory flow rate was limited with a fixed resistance and displayed on a screen so that the subjects could reach a constant inspiratory flow rate of 50, 100 and 150 l/min with a submaximal inspiratory effort. 4. The mean (SD) inspiratory flow rates achieved were 51.4 (5.3), 86.2 (16.6) and 134.4 (22.9) l/min. Baseline forced expiratory volume in 1 s and functional vital capacity were not different on the 3 study days. 5. The cough threshold (geometric mean and 95% confidence intervals) was 21 (9-54) mg/l at an inspiratory flow rate of 50 l/min and 43 (13-141) mg/l at 150 l/min (P less than 0.05). The amount of drug tolerated by the subjects before the cough threshold was achieved was 5.2 (2.0-13.8) mg at an inspiratory flow rate of 50 l/min and 11.6 (3.4-39.8) mg at 150 l/min (P less than 0.05). The number of coughs per inhalation was 1.6 (1.1-2.0) at an inspiratory flow rate of 50 l/min and 1.1 (0.7-1.5) at 150 l/min (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1998

Adding wheat middlings, microbial phytase, and citric acid to corn-soybean meal diets for growing pigs may replace inorganic phosphorus supplementation.

Three experiments were conducted with 96 growing Landrace x Yorkshire x Duroc crossbreds to determine the collective effectiveness of cereal phytase from wheat middlings, microbial phytase, and citric acid in improving phytate-P bioavailability in corn-soy diets. In Exp. 1, 40 gilts (7 wk old) were fed five diets for 8 wk. Diets 1, 2, and 3 were low-P, corn-soybean meal diets (CSB) + 0, .1, or .2% inorganic P (Pi) as calcium phosphate, respectively. Diet 4 was a similar corn-soy diet that included 15% wheat middlings (461 cereal phytase U/kg). Diet 5 was the CSB + microbial phytase (1,200 U/kg; Natuphos, BASF, Mount Olive, NJ). In Exp. 2, 16 barrows (8 wk old) were fed two diets for 6 wk. Diet 1 was the same as Diet 3 of Exp. 1 (.2% Pi). Diet 2 was Diet 4 of Exp. 1 + microbial phytase (300 U/kg). In Exp. 3, 40 barrows and gilts (6 wk old) were fed four diets for 6 wk. Diets 1 and 2 were the same as those in Exp. 2. Diet 3 was Diet 2 of Exp. 2 + 1.5% citric acid. Diet 4 was similar to Diet 3 but contained 10 instead of 15% wheat middlings. In Exp. 1, pigs fed the low-P, CSB (Diet 1) had lower (P < .05) ADG, ADFI, plasma Pi concentration, bone strength, and mobility score than pigs of the other four treatments. Measurements for pigs fed the 15% wheat middlings diet were not significantly different from those of pigs fed the CSB + .1% Pi or microbial phytase. In Exp. 2, ADG (P=.06) during wk 1 to 3 and gain:feed ratio (P < .02) and plasma Pi concentration (P < .005) during all weeks favored pigs fed the CSB + .2% Pi compared with the other diet including 15% wheat middlings. In Exp. 3, identical ADG during all weeks and similar plasma Pi concentrations at wk 4 and 6 were observed between pigs fed the two citric acid diets (Diets 3 and 4) and the CSB + .2% Pi (Diet 1). Pigs fed Diet 4 (10% wheat middlings) had even higher (P < .02) gain:feed ratio during wk 1 to 3 than those fed Diet 1. It seems feasible to completely replace calcium phosphate with 10 to 15% wheat middlings, 300 U microbial phytase/ kg, and 1.5% citric acid in the corn-soy diets for growing pigs.

6-Phytase↗
PubMed1989

The visualization by affinity electrophoresis of a specific association between the consecutive citric acid cycle enzymes fumarase and malate dehydrogenase.

Evidence is growing that the citric acid cycle, like many other metabolic pathways, might exist in vivo as a more or less tightly organized multi-enzyme cluster. The term 'metabolon' [Robinson, J. B. & Srere, P. A. (1985) J. Biol. Chem. 260, 10800-10805] was recently introduced to describe such a complex of sequential metabolic enzymes. We adopted the technique of affinity electrophoresis for the study of interactions between the cycle enzymes fumarase and malate dehydrogenase. This approach offers several advantages over our previously described affinity chromatographic technique [Beeckmans, S. & Kanarek, L. (1981) Eur. J. Biochem. 117, 527-535], one of which is the fact that the interaction can be directly visualized. The observed association is specific since both metabolically unrelated proteins and the cytoplasmic isoenzyme of malate dehydrogenase do not interact with fumarase. Several metabolites (citrate, isocitrate, 2-oxoglutarate, succinate, fumarate, malate, oxaloacetate, Pi, AMP, ADP, NAD+, NADH) were found not to affect the association between fumarase and mitochondrial malate dehydrogenase. Both ATP, Mg2+ -ATP and GTP disrupt the association when they are present at 1 mM concentrations. Lower non-physiological ATP concentrations do not, however, disturb the interaction. The presence of 1 mM ADP was found to abolish the disrupting effect of 1 mM ATP. The latter findings are suggestive of an interruption of the citric acid cycle at the level of fumarase under conditions of high energy load (i.e. high ATP/ADP ratios).

Adenosine Triphosphate↗
PubMed2007

Improved iron bioavailability in an oat-based beverage: the combined effect of citric acid addition, dephytinization and iron supplementation.

BACKGROUND: Iron deficiency in children is a major worldwide nutritional problem. An oat beverage was developed for 1- to 3-year-old children and different treatments were used to improve the iron bioavailability. AIM OF THE STUDY: To investigate the effects of citric acid addition, phytase treatment and supplementation with different iron compounds on non-heme iron absorption in human from a mineral-supplemented oat-based beverage. METHODS: A 240 g portion of a 55Fe-labeled test product (T) or a 59Fe-labeled reference dose (R) was served as breakfast after overnight fasting on four consecutive days in the order of TRRT. On day 18 the retention of 59Fe was measured by a whole-body counter and the erythrocytes uptake of 55Fe and 59Fe by a liquid-scintillation counter. Forty-two healthy subjects (men and women) were randomized into four study groups, members of each being given one of the studied four products (A, B, C, and D) supplemented with Fe (1.3 mg/portion), Zn, Ca, Se and P. Ferric ammonium citrate (FeAC) was added to products A, B, and C and ferric pyrophosphate (FePP) to product D. Citric acid (60 mg/portion) was added to products B, C, and D and phytase treatment applied to products C and D. RESULTS: Citric acid improved iron absorption by 54% from 3.9% in product A to 6.0% in product B (p = 0.051). Phytase treatment increased iron absorption by 78% (from 6.0 to 10.7%, p = 0.003) by reducing the phytate-phosphorus content per portion from 16.3 mg in product B to 2.8 mg in product C. The two compounds gave similar iron absorption rates (p = 0.916). CONCLUSIONS: A combination of citric acid addition, dephytinization and iron supplementation significantly increased the iron absorption in an oat-based beverage. Such a beverage can be useful in the prevention of iron deficiency in 1- to 3-year-old children.

6-Phytase↗
PubMed1996

Mathematical modelling of the citric acid cycle for the analysis of glutamine isotopomers from cerebellar astrocytes incubated with [1(-13)C]glucose.

A mathematical model of the citric acid cycle devoted to the analysis of 13C-NMR data was developed for determining the relative flux of molecules through the anaplerotic versus oxidative pathways and the relative pyruvate carboxylase versus pyruvate dehydrogenase activities. Different variants of the model were considered depending on the reversibility of the conversion of fumarate into malate and oxaloacetate. The model also included the possibility of orientation-conserved transfer of the four-carbon citric acid cycle intermediates, leading to conversion of succinyl-CoA C1 into either malate C1 or C4. It was used to analyse NMR data from glutamine isotopomers produced by cerebellar astrocytes incubated with [1-13C]glucose. Partial cycling (39%) between oxaloacetate and fumarate was evident from the analysis. Application of the model to glutamate isotopomers from granule cells incubated with [1-13C]glucose [Martin, M.. Portais, J.C.. Labouesse. J., Canioni. P, & Merle, M. (1993) Eur. J. Biochem. 217, 617-625] indicated that total cycling of oxaloacetate into fumarate was, in this case, required to get the best fit. The results emphasized some important differences in carbon metabolism between cerebellar astrocytes and granule cells concerning the sources of carbon fuelling the citric acid cycle and the carbon fluxes on different pathways.

Acetates↗
PubMed2000

Effect of sodium chloride and citric acid on growth and toxin production by A. caviae and A. sobria at moderate and low temperatures.

The effect of sodium chloride and citric acid on hemolysin and caseinase production by Aeromonas caviae and Aeromonas sobria at 32 degrees C and 5 degrees C was investigated. At 32 degrees C, although both strains were tolerant to 3% NaCl in TSB, the production of caseinase was decreased in the presence of 1-3% NaCl, and the production of hemolysin was abolished by 2-3% NaCl. Citric acid (0.03%) was less effective than NaCl in reducing hemolysin and caseinase production by both strains at 32 degrees C. A combination of low temperature (5 degrees C) and citric acid treatment reduced hemolysin and caseinase production by both strains. A combination of low temperature (5 degrees C) and NaCl (3%) treatment was the most effective procedure in reducing growth and hemolysin and caseinase production by the tested strains.

Aeromonas↗
PubMed1999

Effect of citric acid on the biosynthesis and composition of xanthan.

The effect of citric acid metabolism by Xanthomonas campestris on composition of xanthan has been studied. Citric acid consumption in fed-batch and continuous fermentation increased the pyruvic acid content of xanthan. An increase in pyruvic acid content in xanthan has been explained with the help of energy balance in xanthan biosynthesis.

Journal Article↗
PubMed2003

Adsorption of citric acid from dilute aqueous solutions by hydroxyapatite.

The role of citric acid in the demineralization of dental enamel, which is mainly constituted by hydroxyapatite, is important for periodontal regeneration and in the conditioning of enamel or dentin for bonding restorative resins. The adsorption of citric acid from aqueous solutions onto synthetic hydroxyapatite at 278, 288, 298, and 308 K and pH 4.8 has been studied by means of UV spectroscopy. The adsorption reaction, which takes place by an interaction between phosphate groups and citrate anions at the solid-solution interface, yields an adsorbate-adsorbent complex of high stability. The adsorption isotherms fit the Langmuirian shape. The proposed adsorption model, where citrate species interact in a bidentate manner (one citrate ion links two phosphate sites), is coherent with the experimental data. The activation standard heat and activation standard entropy were calculated. All the thermodynamic and kinetic parameters were in concordance with the adsorption reaction proposed in this work.

Journal Article↗