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At least 631 records · Page 35Linked to original sources
PubMed1990

Influence of water on bonding of various methacrylates to dentin treated with 10% citric acid-3% ferric chloride solution.

The bond strength of resins (MMA-TBB resin system), containing 2-hydroxyethyl methacrylate (2-HEMA), 3-methacryloyloxypropionic acid (3MPA), 2-phenylethyl methacrylate (Py1EM) and 2-(1-naphthyl) ethyl methacrylate (NEM), to dentin treated with a solution of 10% citric acid and 3% ferric chloride was measured after being immersed in water at 37 degree C for a long period of time to investigate the influence of water on bonding, and the relationship between the monomer structure and the decrease in bond strength in water. The bond strength of the resins did not change with the time spent immersed in water up to 6 months, but decreased with any further increase in time. The decrease in bond strength of all the resins tested was caused by either the degeneration and swelling of collagen or a difference in the degradation of the resin inside and outside the acid-proof dentin layer. There was no significant relationship between the decrease in bond strength in water and the monomer structure.

Acid Etching, Dental↗
PubMed2000

Iron and citric acid: a fuzzy chemistry of ubiquitous biological relevance.

This paper briefly presents a review concerning the species which can arise when iron salts and citric acid are mixed together. The data commented on are required for a correct interpretation of the chemical processes which play a paramount role in biology and in the biological studies involving iron-citrate complexes.

Citrates↗
PubMed1999

Modifications of citric acid cycle activity and gluconeogenesis in streptozotocin-induced diabetes and effects of metformin.

To better define the modifications of liver gluconeogenesis and citric acid cycle, or Krebs' cycle, activity induced by insulin deficiency and the effects of metformin on these abnormalities, we infused livers isolated from postabsorptive or starved normal and streptozotocin-induced diabetic rats with pyruvate and lactate (labeled with [3-13C]lactate) with or without the simultaneous infusion of metformin. Lactate and pyruvate uptake and glucose production were calculated. The 13C-labeling pattern of liver glutamate was used to calculate, according to Magnusson's model, the relative fluxes through Krebs' cycle and gluconeogenesis. These relative fluxes were converted into absolute values using substrate balances. In normal rats, starvation increased gluconeogenesis, the flux through pyruvate carboxylase-phosphoenolpyruvate carboxykinase (PC-PEPCK), and the ratio of PC to pyruvate dehydrogenase (PDH) flux (P < 0.05); metformin induced only a moderate decrease in the PC:PDH ratio. Livers from postabsorptive diabetic rats had increased lactate and pyruvate uptakes (P < 0.05); their metabolic fluxes resembled those of starved control livers, with increased gluconeogenesis and flux through PC-PEPCK. Starvation induced no further modifications in the diabetic group. Metformin decreased glucose output from the liver of starved diabetic rats (P < 0.05). The flux through PC-PEPCK and also pyruvate kinase were decreased (P < 0.05) by metformin in both groups of diabetic rats. In conclusion, insulin deficiency increased in this model of diabetes gluconeogenesis through enhanced uptake of substrate and increased flux through PC-PEPCK; metformin decreased glucose production by reducing the flux through PC-PEPCK.

Animals↗
PubMedDate not supplied

[Enzyme activity of citrate, glyoxylate and pentosephosphate cycles during synthesis of citric acids by Candida lipolytica].

The activity of key enzymes of the citrate and glyoxylate cycles was compared in yeast cells during intensive synthesis of citric acids and in its absence in the course of growth of Candida lipolytica on glucose ("glucose" yeast cells) and on hexadecane ("hexadecane" yeast cells). Citrate and isocitrate were found to be formed by the yeast in the tricarboxylic acid cycle. The ability of the yeast for "overproduction" of citrate and isocitrate during its growth on glucose and hexadecane depends on the high activity of the key enzyme of cycle, citrate synthase, as compared with the activity of other enzymes of the tricarboxylic acid cycle. Citrate predominated among excreted acids during growth on glucose in conditions of nitrogen deficiency while isocitrate prevailed during growth on hexadecane. The predominating synthesis of citrate in the first case seems to be related to a lower activity of aconitase in the "glucose" cells as compared with the "hexadecane" cells.

Aconitate Hydratase↗
PubMed2001

Citric acid ingestion: a life-threatening cause of metabolic acidosis.

We present a case that illustrates the acute (<6 hours) metabolic and hemodynamic effects of the ingestion of a massive oral citric acid load. The principal findings included metabolic acidosis accompanied by an increase in the plasma anion gap that was not caused by L -lactic acidosis, hyperkalemia, and the abrupt onset of hypotension. A unique feature was a dramatic clinical improvement when ionized calcium was infused. The case illustrates the importance of considering the properties of the conjugate base (anion) of the added acid because, in this instance, the citrate anion had a unique and life-threatening consequence (lower ionized calcium level) that was rapidly reversible.

Acid-Base Equilibrium↗
PubMed1991

Periodontal repair in dogs: effect of root surface treatment with stannous fluoride or citric acid on root resorption.

This study evaluated healing, with emphasis on root resorption, following root surface treatment with 1% aqueous stannous fluoride (SnF2), saturated citric acid (CA), or saline control (C) in conjunction with periodontal flap surgery. Supraalveolar periodontal defects were surgically created and immediately treated in the mandibular premolars in 6 beagle dogs. The defect height approximated 5 to 6 mm from the reduced alveolar bone to the cemento-enamel junction. Root treatments were rotated between experimental teeth within jaw quadrants and duplicated in left and right quadrants in the dogs. Flaps were raised to cover most of the crowns of the teeth and sutured. The dogs were sacrificed 12 weeks after surgery and tissue blocks with teeth and adjacent structures were processed for histometric analysis. SnF2-treated teeth healed with significantly longer junctional epithelium, less connective tissue repair to the root surface, and less bone regeneration than CA and C-treated teeth. New cementum formation was limited in all treatment groups. Root resorption was observed in almost all teeth exhibiting connective tissue repair, however to a lesser amount and not as frequent in SnF2 treated teeth due to limited connective tissue repair. No differences were found in amount and frequency of root resorption in CA and C-treated teeth. An inhibitory effect on root resorption of SnF2 could not be disclosed in this experiment, however, it may be concluded that CA treatment of the root surface in conjunction with reconstructive periodontal flap surgery does not seem to enhance root resorption.

Alveolar Process↗
PubMed1995

Proposed role for a combination of citric acid and ascorbic acid in the production of dietary iron overload: a fundamental cause of disease.

This paper presents a review of the significant body of literature liking dietary iron overload, not only to heart disease, but also to cancer, diabetes, osteoporosis, arthritis, and possibly other disorders. Following an analysis of our understanding of the mechanistic role iron plays in oxidative damage, an interpretation of the fact that plasma concentrations of several antioxidants are decreased in the presence of disease is offered. Evaluation of (1) age-related dietary trends over time and (2) factors involved in iron absorption leads to the hypothesis that the combination of citric acid and ascorbic acid (a synergistic pair of strong enhancers) is instrumental in causing a deleterious increase in iron load in aging populations. Iron overload may be the most important common etiologic factor in the development of the diseases mentioned; therefore, the synergistic combination of citric and ascorbic acids may play a major role in our worsening disease statistics. Evidence to support this hypothesis and possible experiments to test it are included. This combination needs further study, particularly because the iron overload produced may be correctable.

Aging↗
PubMed1991

Comparison of different strains of the yeast Yarrowia lipolytica for citric acid production from glucose hydrol.

Four commercial strains and two mutants of the yeast species Yarrowia lipolytica were screened using batch fermentation. Strain Y. lipolytica A-101-1.14 (induced with UV irradiation) was found to be the most suitable for citric acid production from glucose hydrol (39.9% glucose and 2.1% other sugars), a byproduct of glucose production from potato starch. The specific rate of total citric and isocitric acid production was 0.138 g/g.h, the yield on consumed glucose 0.93 g/g, and the productivity achieved was as high as 1.25 g/L.h. All of the tested yeast strains were able to utilize only the glucose from the glucose hydrol medium. Thus, some residual higher oligosaccharides remained in the process effluent.

Citrates↗
PubMed1987

The role of the citric acid cycle in fungal organic acid fermentations.

Filamentous fungi are well known for their potential to accumulate organic acids in the medium when supplied with large amounts of sugar. Commercial applications of this are the production of citric and itaconic acids. The present review attempts to present the current state of knowledge on the biochemical basis of organic acid accumulation by filamentous fungi (citric, itaconic, fumaric and oxalic acids), particularly with respect to the role of citric acid cycle reactions. The explanations offered are based on recent advances in understanding the compartmentation of the fungal cell, and regulation of some key enzymes. The general conclusion is that fungi accumulate organic acids by mechanisms which avoid the channeling of substrates into the citric acid cycle under conditions of strongly active glycolysis.

Carboxylic Acids↗
PubMed1996

The puzzle of the Krebs citric acid cycle: assembling the pieces of chemically feasible reactions, and opportunism in the design of metabolic pathways during evolution.

The evolutionary origin of the Krebs citric acid cycle has been for a long time a model case in the understanding of the origin and evolution of metabolic pathways: How can the emergence of such a complex pathway be explained? A number of speculative studies have been carried out that have reached the conclusion that the Krebs cycle evolved from pathways for amino acid biosynthesis, but many important questions remain open: Why and how did the full pathway emerge from there? Are other alternative routes for the same purpose possible? Are they better or worse? Have they had any opportunity to be developed in cellular metabolism evolution? We have analyzed the Krebs cycle as a problem of chemical design to oxidize acetate yielding reduction equivalents to the respiratory chain to make ATP. Our analysis demonstrates that although there are several different chemical solutions to this problem, the design of this metabolic pathway as it occurs in living cells is the best chemical solution: It has the least possible number of steps and it also has the greatest ATP yielding. Study of the evolutionary possibilities of each one-taking the available material to build new pathways-demonstrates that the emergence of the Krebs cycle has been a typical case of opportunism in molecular evolution. Our analysis proves, therefore, that the role of opportunism in evolution has converted a problem of several possible chemical solutions into a single-solution problem, with the actual Krebs cycle demonstrated to be the best possible chemical design. Our results also allow us to derive the rules under which metabolic pathways emerged during the origin of life.

Acetates↗
PubMed2005

Effect of citric acid on aluminum hydrolytic speciation.

The mechanisms of the influence of organics on Al transformation were not fully understood. This study investigated the effect of citric acid on Al speciation in partially neutralized aluminum solution. The partially neutralized solution was prepared with 20 mmol L(-1) AlCl3 without citrate (citrate/Al molar ratio of 0, control) or with citrate (citrate to Al molar ratios between 0.1 and 3.0) at pH between 3.0 and 7.0. The nature of aluminum hydrolytic products as influenced by citrate complexation was investigated by turbidity measurement, ferron kinetic color development, peak line width in 27Al nuclear magnetic resonance (NMR) deconvolution demodule quantitative methods, and the MinteqA2 chemical speciation program. Sulfate precipitates from Al solution as influenced by citrate were examined by X-ray diffraction (XRD) analysis and atomic force microscopy (AFM). The turbidity of the Al solution increased with increasing pH values. Increases in citrate/Al molar ratio from 0 to 0.1 decreased dramatically the turbidity due to citrate complexation. The 27Al NMR peak at 6 ppm of the Al solution at a citrate/Al molar ratio of 0.5 shifted to 8 and 10 ppm in the solutions at citrate/Al molar ratio of 1.0 and 3.0, respectively. Comparison of 27Al NMR data and the data obtained from the MinteqA2 chemical speciation program, indicate that the Al-citrate complexes as revealed by 27Al NMR data are largely Al(citrate), AlH(citrate)+, and Al(citrate)(2)3- complexes (99-112%) in the pH range of 4.5-6.5. The non-detected Al fractions by the MinteqA2 program account for 82-99% of the non-detected Al fractions by NMR quantitation in the same pH range. The AFM of sulfate precipitates from solutions with low citrate/Al molar ratios (i.e., 0.01, pH 4.5, aged 40 days) shows that Al13 sulfate precipitates were ellipse-shaped. These ellipse-shaped precipitates were aggregated when solution pH increased from 4.5 to 7.0 (aged 40 days), indicating the fast hydrolytic rate of Al at high pH. The sulfate precipitates from solution with a high citrate/Al molar ratio (i.e., 0.05, pH 4.5, aged 40 days) also shows aggregate of particles, and XRD non-crystallized precipitates the hampering effect of citrate on Al precipitates.

Aluminum↗
PubMed1997

Sodium metabisulfite and citric acid induce bronchoconstriction via a sulfite-sensitive pathway in the isolated guinea pig lung.

Inhalation of sodium metabisulfite (MBS; 80 mM; pH 2.9 +/- 0.1) or citric acid (CA; 0.4 M; pH 2.0 +/- 0.1) aerosols induced a reduction in compliance and conductance in the isolated perfused and ventilated guinea pig lung without affecting perfusion flow. The effect was dependent on the pH of the nebulized solution since inhalation of 80 mM MBS aerosols at pH 7.4 did not induce any effect on bronchial tone. Concomitantly to the bronchoconstriction induced by MBS or CA an increased level of calcitonin gene-related peptide (CGRP-LI) in the effluent perfusate was observed, indicating activation of sensory nerves. Sodium sulfite, a dissolution product of MBS, has previously been shown by our studies to reduce bronchoconstriction induced by inhalation of sulfur dioxide, in the isolated perfused and ventilated guinea pig lung. In the present study perfusion of the lung with sodium sulfite (3 mM) before and during exposure to aerosols with either MBS or CA attenuated the bronchoconstriction induced by the acidic solutions. The release of CGRP-LI induced by MBS or CA was not affected by sodium sulfite. Sulfite treatment did not modify perfused guinea pig lung reactivity towards acetylcholine (4 nmol), bradykinin (100 pmol), histamine (10 nmol), serotonin (500 pmol) and substance P fragment 5-11, a substance P analogue resistant to degrading enzyme (500 pmol). However, an inhibitory effect by sodium sulfite was observed on bronchoconstriction induced by the NK-2 agonist neurokinin A fragment 4-10 (NKA 4-10, 25 pmol). These results indicate that MBS- or CA-induced bronchoconstriction was dependent on the low pH of the aerosol solution and coincided with activation of sensory nerves. Sulfite modulation of the bronchoconstricting action of inhaled MBS and CA is suggested to be related to a sulfite-sensitive step in the signal transduction of the neuropeptide NKA.

Acetylcholine↗
PubMed1977

Effect of primidone concentration on glass transition temperature and dissolution of solid dispersion systems containing primidone and citric acid.

The glass transition temperatures of glasses containing various concentrations of primidone in citric acid were measured and found to increase as the primidone concentration increased. Dissolution studies of these systems and particle-size measurements of primidone precipitated during dissolution of devitrified glasses suggest that the increase in the dissolution rate of the devitrified systems is due to both the small size of the precipitated crystals and the excellent wettability of these systems.

Chemistry, Pharmaceutical↗
PubMed1984

Enzymes of the Poly-beta-Hydroxybutyrate and Citric Acid Cycles of Rhizobium japonicum Bacteroids.

The activities of several enzymes of the citric acid and poly-beta-hydroxybutyrate cycles were measured in Rhizobium japonicum 3I1B-143 bacteroids which had been isolated from soybean nodules by sucrose gradient centrifugation. During the period of developing nitrogenase activity, the specific activity of fumarase, hydroxybutyrate dehydrogenase, beta-ketothiolase, and pyruvate dehydrogenase complex increased whereas acetoacetate-succinyl-CoA transferase and isocitrate dehydrogenase decreased. Malate dehydrogenase activity remained constant. The amount of available acetyl-CoA, based on pyruvate dehydrogenase activity, should be sufficient to support both metabolic cycles concurrently. The temporal relationship between nitrogenase activity and poly-beta-hydroxybutyrate accumulation has been reexamined.

Journal Article↗
PubMed1967

A study of Krebs citric acid cycle enzymes in rice moth larvae (Corcyrace phalonica St) during mycotoxicosis.

Krebs citric acid cycle enzymes have been studied in rice moth larvae (Corcyra cephalonica St) reared in groundnut meal control and contaminated with A. flavus, wheat bran control and wheat bran contaminated with A. flavus and also wheat bran containing aflatoxin. It was observed that the activity of enzymes other than succinic oxidase, succinic dehydrogenase and isocitric dehydrogenase were reduced significantly in larvae reared in contaminated groundnut meal when compared with the control. In the case of larvae reared in contaminated wheat bran all the enzymes except succinic oxidase were inhibited when compared to the control larvae. It was also observed that the inhibition of these enzymes is greater in the case of larvae reared in contaminated wheat bran than in contaminated groundnut meal. The higher toxicity of wheat bran has been discussed.

Aflatoxins↗
PubMed1991

Changes in development and ultrastructure of Aspergillus niger mycelium in the presence of toxic substances from molasses in citric acid fermentation medium.

Effects of a surface-active agent (Spumol BJ) and toxic molasses compounds on development and ultrastructure of Aspergillus niger strain R-16 mycelium producing citric acid in surface fermentation on molasses medium with 80% yield are presented. Microscopic observations showed that Spumol BJ in concentration of 5 microliters/100 cm3 as well as toxic molasses compounds stimulated the process of swelling and germinating of conidia. Giant conidia unable to germinate, appeared along with typical ones. Delicate mycelium outgrowing from germinating conidia however, sank after 20-24 h culture. Observations of hyphae in electron microscope showed changes in the ultrastructure and dimensions of mitochondria followed by successive degeneration of protoplast. The data obtained indicate that one of the reasons disqualifying raw molasses for biotechnological processes might be the excessive amount of surface-active antifoaming additives.

Aspergillus niger↗