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PubMed1987

The role of the citric acid cycle in cells of the immune system and its importance in sepsis, trauma and burns.

Many aspects of the cell biology of lymphocytes and macrophages have been studied extensively over many years. Our recent work on these cells has investigated the fuels utilized, the metabolism carried out and the importance of this metabolism for the specific function of these cells in the immune system. The quantitatively important role of glutamine and the observation that both glutamine and glucose are only partially oxidized by both types of cell have been established. This work has led to a new hypothesis to explain the high rates of partial oxidation of both fuels in lymphocytes and macrophages, and in other cells such as enterocytes, colonocytes and also in neoplastic cells. In addition, the high rate of glutamine utilization and its importance in such cells has raised the question as to the source of this glutamine in the body: the evidence suggests that this is muscle. The metabolic relationship between the glutamine-producing tissue and the cells of the immune system provides an explanation for some well-established changes in metabolism during the condition of surgery, trauma, sepsis and burns. Knowledge of the metabolism of glucose, glutamine, pyruvate and long-chain fatty acids by these cells raises some intriguing questions concerning the role and function of the citric acid cycle in these and other similar cells, including tumour cells.

Animals↗

PubMed2005

Influence of dissolved oxygen concentration on intracellular pH for regulation of Aspergillus niger growth rate during citric acid fermentation in a stirred tank bioreactor.

In this paper we report the regulation of Aspergillus niger growth rate during citric acid fermentation in a stirred tank bioreactor. For this, the influence of dissolved oxygen concentration in a medium on intracellular pH values and consequently on overall microbial metabolism was emphasized. Intracellular pH of mycelium grown under different concentrations of dissolved oxygen in the medium was determined. Sensitivity of proteins toward proton concentration is well recognized, therefore pH influences on the activities of key regulatory enzymes of Aspergillus niger were determined at pH values similar to those detected in the cells grown under lower dissolved oxygen concentrations. The results have shown significantly reduced specific activities of hexokinase, 6-phosphofructokinase and glucose-6-phosphate dehydrogenase in more acidic environment, while pyruvate kinase was found to be relatively insensitive towards higher proton concentration. As expected, due to the reduced specific activities of regulatory enzymes under more acidic conditions, overall metabolism should be hindered in the medium with lower dissolved oxygen concentration which was confirmed by detecting the reduced specific growth rates. From the studies, we conclude that dissolved oxygen concentration affects the intracellular pH and thus growth rate of Aspergillus niger during the fermentation process.

Aspergillus niger↗

PubMed1986

Cough response to citric acid aerosol in occasional smokers.

Twenty two normal women volunteers underwent a standard cough provocation test by inhaling solutions of citric acid of progressively increasing concentration. Eight were non-smokers, eight moderate smokers, and six occasional smokers. All the non-smokers and moderate smokers coughed. Moderate smokers tended to cough more than non-smokers, but not significantly so. None of the occasional smokers coughed at all (p less than 0.001). Possibly the ability to smoke occasionally with enjoyment is a marker for a diminished cough reflex.

Adult↗

PubMed1984

Effect of sustained portal-systemic shunting on glycolytic and citric-acid cycle intermediates in the rat brain.

The effect of portacaval (PC) shunting on brain glycogen, glucose, glycolytic and citric-acid cycle intermediates was analysed in rats shunted for 3, 8 and 16 weeks. Portal-systemic shunting was accompanied by a progressive fall in brain glucose which was reduced to about half of control after 16 weeks of shunting (P less than 0.05). Glycogen remained unchanged. Glucose-6-phosphate and fructose-1,6-diphosphate were significantly (P less than 0.05) increased and decreased, respectively, which may indicate some inhibition of phosphofructokinase. These changes in brain glucose content and glycolysis may be additive to any further metabolic perturbation and provide one tentative mechanism of sensitization of the brain in liver failure.

Ammonia↗

PubMed1984

Inhibition by alloxan of mitochondrial aconitase and other enzymes associated with the citric acid cycle.

Considerable variations were found in the in vitro effect of alloxan on mouse liver enzymes associated with the citric acid cycle. The following approximative alloxan concentrations induced 50% inhibition of enzyme activity: 10(-6)M for aconitase, 10(-4)M for NAD-linked isocitrate dehydrogenase, glutamate dehydrogenase, alpha-ketoglutarate dehydrogenase, succinyl-CoA synthetase and fumarase, and 10(-3)M for citrate synthase and NADP-linked isocitrate dehydrogenase. Pyruvate dehydrogenase, succinate dehydrogenase and malate dehydrogenase were not inhibited by 10(-3)M alloxan. The inhibition of aconitase was competitive both when using mouse liver and purified porcine heart enzyme. The Ki values for the purified enzyme in the presence of 5 microM alloxan were 0.22 microM with citrate, 4.0 microM with cis-aconitate and 0.62 microM with isocitrate as substrate. The high sensitivity of aconitase for inhibition by alloxan probably plays a prominent role for the toxic effects of alloxan.

Aconitate Hydratase↗

PubMed2000

Citric acid etching of cervical sclerotic dentin lesions: an AFM study.

Atomic force microscopy (AFM) has been used to determine microstructural changes, etching rates of peritubular dentin, and intertubular dentin recession during demineralization in dilute acidic solutions. These studies have not included many forms of altered dentin, including noncarious sclerotic root dentin associated with Cl V (abfraction) lesions. We sought to determine microstructural changes and recession rates during demineralization in citric acid (pH 2.5, 0.018M) for the transparent/sclerotic zone. Highly polished dentin disks were prepared from teeth with noncarious C1 V lesions (n = 3) and compared with normal root dentin (n = 3). Samples were etched at 5-s intervals for 1 min and at longer intervals up to 30 min. The depth changes in various portions of the dentin with respect to the reference layer were measured and changes in microstructure observed in solution in the wet cell of the AFM. In sclerotic dentin, most tubule lumens were occluded with crystalline deposits that etched more slowly than the other dentin components, but etching rates could not be determined due to their irregular geometry. The intertubular dentin recession quickly reached a plateau after a depth change of <1 microm for all dentin types, in agreement with prior work. Mixed linear regression models indicated an important difference between the etching of sclerotic intertubular dentin and that of non-sclerotic root dentin that became apparent after 600 s (p = 0.037). The sclerotic intertubular dentin underwent less depth change at the plateau (558 nm) compared to normal root dentin (744 nm). In addition, normal root dentin underwent significantly greater recession than coronal dentin (p = 0.002). The results of this study indicate that intertubular sclerotic dentin from Cl V lesions etches differently than normal root dentin, and this may help explain the difficulties in restoring such lesions with current bonding procedures.

Acid Etching, Dental↗

PubMedDate not supplied

Enzymatic-ultraviolet determination of L-citric acid in wine: collaborative study.

A collaborative study was carried out on an enzymatic method for the determination of L-citric acid in wine, using the enzymes citrate lyase, malate dehydrogenase, and lactate dehydrogenase and the coenzyme nicotinamide-adenine dinucleotide phosphate. The study was performed by 18 laboratories using 4 blind duplicates of commercial wine. The method is simple and shows good precision. Coefficients of variation (CV) for reproducibility ranged from 1.8 to 3.4%; CVs for repeatability ranged from 0.76 to 2.62%. Analysts are cautioned to check the linear absorbance response of their spectrophotometers when performing this assay and also to take care in pipetting the relatively small volumes used in this procedure. The method has been adopted official first action.

Citrates↗

PubMed1982