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PubMed1987

Regulation of the enzymes at the branchpoint between the citric acid cycle and the glyoxylate bypass in Escherichia coli.

During growth of Escherichia coli on acetate, the glyoxylate bypass supplies the precursors needed for biosynthesis. The glyoxylate bypass enzyme isocitrate lyase competes with the citric acid cycle enzyme isocitrate dehydrogenase for the available isocitrate. We have studied the control of metabolic flux at this branchpoint by examining the regulatory properties of the enzymes concerned. Isocitrate dehydrogenase is controlled by reversible phosphorylation catalysed by a bifunctional kinase/phosphatase whose activities are regulated by isocitrate, biosynthetic precursors and adenine nucleotides. The flux through isocitrate lyase is mainly controlled by the intracellular concentration of isocitrate. The phosphorylation system responds to the availability of energy and precursors and maintains isocitrate at a concentration high enough to sustain the flux through the glyoxylate bypass necessary for biosynthesis.

Citric Acid Cycle↗
PubMed2000

Simple diffusion is the primary mechanism for glucose uptake during the production phase of the Aspergillus niger citric acid process.

Models for the known glucose transporters in Aspergillus niger and for simple diffusion of glucose through the hyphal membrane were prepared. The results from the models were compared with fermentation data from published studies on citric acid. It was found that the purely physical and uncontrolled process of diffusion could explain the specific rate of glucose uptake observed during the production phase in several different types of fermentation.

Aspergillus niger↗
PubMed2005

Use of hydrogen peroxide in combination with nisin, sodium lactate and citric acid for reducing transfer of bacterial pathogens from whole melon surfaces to fresh-cut pieces.

Hydrogen peroxide (2.5%) alone or hydrogen peroxide (1%) in combination with nisin (25 microg/ml), sodium lactate (1%), and citric acid (0.5%) (HPLNC) were investigated as potential sanitizers for reducing Escherichia coli O157:H7 or Listeria monocytogenes populations on whole cantaloupe and honeydew melons. Whole cantaloupes inoculated with E. coli O157:H7 and L. monocytogenes at 5.27 and 4.07 log10 CFU/cm2, respectively, and whole honeydew melons inoculated with E. coli O157:H7 and L. monocytogenes at 3.45 and 3.05 log10 CFU/cm2, respectively, were stored at 5 degrees C for 7 days. Antimicrobial washing treatments were applied to inoculated whole melons on days 0 or 7 of storage and surviving bacterial populations and the numbers transferred to fresh-cut pieces were determined. At days 0 and 7 treatment with HPLNC significantly (p<0.05) reduced the numbers of both pathogens, by 3 to 4 log CFU/cm2 on both types of whole melon. Treatment with HPLNC was significantly (p<0.05) more effective than treatment with 2.5% hydrogen peroxide. While fresh-cut pieces prepared from stored whole melons were negative for the pathogens by both direct plating and by enrichment, fresh-cut pieces from cantaloupe melons treated with 2.5% hydrogen peroxide were positive for both pathogens and pieces from honeydew melons were positive for E. coli 0157:H7. The native microflora on fresh-cut melons were also substantially reduced by HPLNC treatment of whole melons. The results suggest that HPLNC could be used to decontaminate whole melon surfaces and so improve the microbial safety and quality of fresh-cut melons.

Anti-Bacterial Agents↗
PubMed1980

Propionate inhibition of succinate:CoA ligase (GDP) and the citric acid cycle in mitochondria.

Propionate inhibits oxygen consumption by rat liver mitochondria when glutamate, alpha-ketaglutarate, and succinate are substrates. Carnitine prevents this effect. The pattern of inhibition of 14CO2 release from metabolic intermediates indicates citric acid cycle inhibition between succinate:coenzyme A (CoA) ligase (GDP) and malate dehydrogenase. Propionyl CoA is synthesized from propionate in mitochondria. Propionyl CoA is a potent inhibitor of succinate:CoA ligase with positive cooperativity and half half-maximal inhibition at 2 X 10(-4) M propionyl CoA.

Acyl Coenzyme A↗
PubMed1998

Effect of citric acid supplements to a maize-soya diet on the in vitro availability of minerals, trace elements, and heavy metals.

The aim of the present study was to evaluate the effect of increasing supplements of citric acid (CTA) on the in vitro availability of mineral (Ca, Mg), trace elements (Mn, Zn) and heavy metals (Pb, Cd). Phytaterich diets (0.8%) based on maize, soybean meal, corn starch and soybean oil (containing 5.0 g Ca, 1.2 g Mg, 50 mg Mn, 22 mg Zn, 10 mg Pb and 5 mg Cd per kg diet) were supplemented with 0, 1, 2, 3 and 4% of CTA. All diets were treated in a multi-enzyme in vitro system followed by equilibrium dialysis after peptic and pancreatic digestion. Under the conditions investigated, dietary addition of CTA enhanced dialysability of calcium, magnesium, manganese and zinc. Furthermore, a dose-dependent increase of lead and cadmium dialysability due to CTA supplementations was evident.

Animal Feed↗
PubMed1990

[Detection of antibodies to citric acid extract of skeletal muscle (CAE-ab) in the sera of patients with myasthenia gravis using indirect hemagglutination].

In this paper are described the method and results for the demonstration of the antibodies to citric acid extract of skeletal muscle (CAE-ab) in the sera from myasthenia gravis (MG) patients with or without thymoma, in patients with other diseases and in healthy controls by an indirect hemagglutination assay (IHA), were described. The CAE-ab titers were positive in 15 (71.43%) of the 21 MG patients with thymoma, the antibody titers ranging from 1:16 to 1:512. In the 35 MG patients without thymoma, as well as in the 32 healthy controls and 22 patients with other diseases, the antibody titers were all negative A statistically significant difference was found between the CAE-ab titers in the group of MG patients with thymoma and those in the other three groups. It was considered that IHA for the purpose of demonstrating CAE-ab could serve as a supplementary diagnostic method for early detection of thymoma in MG patients at an early stage.

Adolescent↗
PubMedDate not supplied

Citric acid as a plasticizer for spray-dried microcapsules.

An aqueous spray-drying process was used to coat theophylline particles with a cellulose polymer, sodium carboxymethylcellulose (NaCMC) or hydroxypropylmethylcellulose (HPMC). Effect of a plasticizer, citric acid, was studied. Strength of cast films have a direct relationship to the dissolution T50% values of the respective spray-dried products. With varying plasticizer concentrations, changes in interaction between plasticizer and polymer, and in size of crystallized drug crystals, were observed with HPMC films. The plasticizer content also affected the films of NaCMC by bringing about a change in the form and arrangement of the drug. X-ray diffraction analyses of the different spray-dried products revealed a possibility of the predominance of different crystal forms. Spherical spray-dried microcapsules of NaCMC were formed with a 20-30% w/w plasticizer content. With HPMC, as plasticizer concentration was increased there was a corresponding increase in mean size of the spray-dried products. In terms of drug release and formation of spherical particles, a plasticizer concentration of 30% w/w was found to be suitable for both HPMC and NaCMC.

Capsules↗
PubMed1982

[Scanning and transmission electron microscopy study of the effects of a citric acid solution on the human root dentine].

After removal of the cementum layer, the buccal surface of human roots was been treated in vitro for 60, 120 and 180 seconds with a gel solution of 50% citric acid (pH 2.1). These surfaces were prepared for observation in the scanning electron microscope (SEM) and ultra-thin sections of the treated areas were studied in the transmission electron microscope (TEM). The SEM results showed that application of an acid solution revealed fibrous like structures on the dentinal surface after 60 and 180 seconds of treatment. A correlation between the results obtained in SEM and TEM is not always evident. The ultra-thin sections showed, in the superficial dentine, three distinct zones at the three time intervals chosen: from outside to inside, a very thin crust, a demineralized zone with collagen fibres and a deep dentine zone could be observed. After 120 seconds, the collagenous matrix seemed to be totally freed from the inorganic part.

Adult↗
PubMed1988

Treatment of intraosseous periodontal defects with a combined adjunctive therapy of citric acid conditioning, bone grafting, and placement of collagenous membranes.

A total of 25 proximal, intraosseous periodontal defects were treated in 21 adult patients. A 3-prong adjunctive, regenerative treatment approach was used. The treatment included (1) citric acid conditioning of the root surfaces, (2) grafting of particles of decalcified, freeze-dried homologous bone, and (3) placement of freeze-dried, homologous dura mater sheets between the replaced surgical flaps and the tooth surfaces. The results, as evaluated by probing attachment and probing bone level measurements, during 1 year of observation, demonstrated limited improvements of the treated defects. The limited results were similar to previous observations in our clinics following treatment of intraosseous defects using different treatment modalities. It appears that new treatment approaches need to be sought to accomplish clinically significant and predictable regeneration in proximal, intraosseous periodontal defects.

Adult↗
PubMed2000

The soft tissue response to contaminated and cleaned titanium surfaces using CO2 laser, citric acid and hydrogen peroxide. An experimental study in the rat abdominal wall.

The soft tissue response to clinically retrieved and decontaminated cover screws was evaluated in a rat model. The cover screws were cleaned by using citric acid, sterile water, hydrogen peroxide and CO2 laser alone or with a combination of these. In addition, decontaminated but not cleaned and unused cover screws were used as negative and positive controls, respectively. After cleaning the cover screws were implanted in the abdominal wall of the rat for 6 weeks. The thickness of the fibrous capsule and the number of macrophages within the capsule were measured by means of light microscopical morphometry. As compared to the negative control, CO2 laser on dry surface, CO2 laser + hydrogen peroxide and the positive control had statistically significant thinner fibrous capsules. As compared to the positive, only laser alone resulted in a similar tissue response. It is concluded that CO2 laser used alone or in combination with hydrogen peroxide may be used clinically for sufficient decontamination of titanium surfaces.

Abdomen↗
PubMed1997

Recurrence of mandibular molar furcation defects following citric acid root treatment and coronally advanced flap procedures.

This report concerns long-term (4 to 5 years) clinical evaluation of 22 resolved (complete bone closure) mandibular Class 2 furcation defects following coronally advanced flap procedures and citric acid root treatment with or without adjunctive implantation of freeze-dried, demineralized allogeneic bone. Sixteen buccal furcation sites in 12 patients were available for the follow-up evaluation. The furcation involvement was independently evaluated by a panel of three examiners, each using three furcation index systems. Oral hygiene standards, gingival health, probing depth, clinical attachment level, gingival recession, tooth vitality, and detectable caries or root resorption were also recorded. Mean attachment level at the furcation sites was 5.8 +/- 2.9 mm, compared to 4.5 +/- 2.2 mm and 3.5 +/- 1.3 mm over the prominence of the mesial and distal roots, respectively. The clinical examination further revealed that 12 out of 16 sites exhibited recurrent Class 2 furcation involvement. Of the 16 teeth examined, one had received endodontic treatment, while the remaining 15 responded within the normal range to pulp testing. One tooth had developed caries in the furcation region. No teeth demonstrated periradicular pathology. The results of this study question the long-term stability of furcation bone regeneration following coronally advanced flap procedures.

Bone Transplantation↗
PubMed1983

Pulpal effect of citric acid applied topically to root surfaces.

Five beagle dogs were subjected to the raising of full-thickness flaps on the buccal aspects of premolar teeth. Approximately 7 mm. of buccal bone was removed to expose the root surfaces, which were treated with 20 percent citric acid. Saline was used as a control, and after periods of 1, 7, 14, 28, and 56 days, the animals were killed. Specimens were examined histopathologically when microscopic examination failed to detect any pulpal changes in either the experimental or the control specimens.

Administration, Topical↗
PubMed1988

Evaluation of carbon flux and substrate selection through alternate pathways involving the citric acid cycle of the heart by 13C NMR spectroscopy.

A previous 13C NMR technique (Malloy, C. R., Sherry, A.D., and Jeffrey, F.M.H. (1987) FEBS Lett. 212, 58-62) for measuring the relative flux of molecules through the oxidative versus anaplerotic pathways involving the citric acid cycle of the rat heart has been extended to include a complete analysis of the entire glutamate 13C spectrum. Although still simple in practice, this more sophisticated model allows an evaluation of 13C fractional enrichment of molecules entering both the oxidative and anaplerotic pathways under steady-state conditions. The method was used to analyze 13C NMR spectra of intact hearts or their acid extracts during utilization of 13C-enriched pyruvate, propionate, acetate, or various combinations thereof. [2-13C]Pyruvate was used to prove that steady-state flux of pyruvate through pyruvate carboxylase is significant during co-perfusion of pyruvate and acetate, and we demonstrate for the first time that a nine-line 13C multiplet may be detected in an intact, beating heart. Acetate or pyruvate alone provided about 86% of the acetyl-CoA; in combination, about 65% of the acetyl-CoA was derived from acetate, about 30% was derived from pyruvate, and the remainder from endogenous sources. Propionate reduced the contribution of exogenous acetate to acetyl-CoA to 77% and also reduced the oxidation of endogenous substrates. Equations are presented which allow this same analysis on multiply labeled substrates, making this technique extremely powerful for the evaluation of substrate selection and relative metabolic flux through anaplerotic and oxidative pathways in the intact heart.

Acetates↗
PubMed1977

Regulation of the central metabolism in relation to citric acid production in Saccharomycopsis lipolytica.

The mechanism of the massive extracellular production of citric and isocitric acids by Saccharomycopsis lipolytica grown on n-paraffins has been studied. When growth stops, because of nitrogen limitation, the intracellular concentration of ATP sharply rises whereas that of AMP and ADP decreases to a low level. At the same time production of acids begins. The activity of the NAD-dependent isocitrate dehydrogenase which requires AMP for activity becomes very low and prevents the oxidative function of the citric acid cycle whereas isocitrate lyase is not inhibited. As citrate synthase inhibition by ATP appears to be insufficient to stop n-paraffin degradation, citric and isocitric acids accumulation can take place. Massive excretion of these acids, however, probably still involves other physiological changes brought about by nitrogen limitation, possibly some permeabilization of the cell to these acids.

Acetates↗
PubMed1997

The expanded Hansen approach to solubility parameters. Paracetamol and citric acid in individual solvents.

In this study two solubility-parameter models have been compared using as dependent variables the logarithm of the mole fraction solubility, lnX2e, and ln(alpha)/U (originally used in the extended Hansen method), where alpha is the activity coefficient and U is a function of the molar volume of the solute and the volume fraction of the solvent. The results show for the first time the proton-donor and -acceptor hydrogen-bonding capacities of paracetamol, as measured by the acidic and basic partial-solubility parameters. The influence of solvents on the differential scanning calorimetry (DSC) pattern of the solid phases was also studied in relation to the solubility models tested. Citric acid was chosen as a test substance because of its high acidity and its proton donor capacity to form hydrogen bonds with basic solvents. The partial acidic and basic solubility parameters obtained from multiple regression were consistent with this property, validating the model chosen. The results show that the more direct lnX2e variable was more suitable for fitting both models, and the four-parameter model seemed better for describing the interactions between solvent and solute.

Acetaminophen↗
PubMed1994

Effect of inhaled menthol on citric acid induced cough in normal subjects.

BACKGROUND: Menthol is a commonly used ingredient in many over the counter cough remedies, but there is little objective evidence as to its efficacy. METHODS: Twenty healthy subjects received a cough challenge consisting of five inhalations of 33 mumol citric acid from an air driven dosimeter. The challenge was repeated at hourly intervals for five hours. Five minutes before each challenge subjects inhaled, in a randomised design, either menthol 75% in eucalyptus oil or one of two placebos (pine oil or air). RESULTS: Menthol inhalation caused a reduction in evoked cough when compared with either placebo. CONCLUSIONS: Menthol is an effective antitussive agent in an evoked cough model.

Administration, Inhalation↗
PubMed1993

[Citric acid as an adjunct to periodontal surgery].

This review focuses on the effect of acid demineralisation of the root surface as an adjunct to periodontal surgery in order to obtain new attachment. Several animal studies have shown that the treatment facilitates attachment of connective tissue to the root surface. Clinical studies, however, have failed to demonstrate the effectiveness of citric acid as an adjuvant to surgical debridement.

Animals↗
PubMed1991

Quantification of cell nuclei isolated from hepatocytes by cell lysis with nonionic detergent in citric acid.

A method was developed for determining the number of nuclei of hepatocytes cultured on collagen gel using a nonionic detergent, Nikkol BO-10TX. The cells were recovered in a test tube after solubilizing the gel by incubating it with the detergent in 0.1 M citric acid and then centrifuging the mixture. Nuclei were isolated from the cells with the same detergent solution and collected by centrifugation. The numbers of nuclei in cultures, scored with a hemocytometer or an electronic particle counter, were proportional to the lactate dehydrogenase activities of the cells. This method was also applicable for scoring the number of nuclei of hepatocytes cultured on collagen-coated plastic.

Animals↗