SEARCH · Search PubMed

Results for “CITRATES”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 793 records · Page 44Linked to original sources

PubMed1976

Urinary citrate excretion in stone-formers and normal controls.

A specific method was used for the estimation of citrate in 24-hour urine collections from 108 young adult controls, 158 patient controls and 164 stone-formers. Stone-formers excreted significantly less citrate in 24 hours than either patient controls or young adult controls. Stone-formers had a lower concentration of citrate in their urine than either of the control groups. The young adult females exhibited a much greater excretion of citrate relative to calcium than the young males. Because of the ability of citrate to complex with calcium ions and keep them in solution, the relatively low incidence of calcium-containing stones in females under 50 years of age could well be the result of their high excretion of citrate and their increased excretion of this substance relative to calcium.

Adolescent↗

PubMed2000

Properties of Aspergillus niger citrate synthase and effects of citA overexpression on citric acid production.

Using a combination of dye adsorption and affinity elution we purified Aspergillus niger citrate synthase to homogeneity using a single column and characterised the enzyme. An A. niger citrate synthase cDNA was isolated by immunological screening and used to clone the corresponding citA gene. The deduced amino acid sequence showed high similarity to other fungal citrate synthases. After processing upon mitochondrial import, the calculated M(r) of A. niger citrate synthase is 48501, which agrees well with the estimated molecular mass of the purified protein (48 kDa). In addition to an N-terminal mitochondrial import signal, a peroxisomal target sequence (AKL) was found at the C-terminus of the protein. Whether both signals are functional in vivo is not clear. Strains overexpressing citA were made by transformation and cultured under citric acid-producing conditions. Up to 11-fold overproduction of citrate synthase did not increase the rate of citric acid production by the fungus, suggesting that citrate synthase contributes little to flux control in the pathway involved in citric acid biosynthesis by a non-commercial strain.

Acetyl Coenzyme A↗

PubMed1983

The influence of citrate on platelet aggregation and malondialdehyde production.

3 commonly used parameters for platelet aggregability were tested for their dependence on citrate concentrations. Relatively minor changes in citrate concentrations markedly influenced ADP threshold values for secondary aggregation. Collagen induced platelet malondialdehyde (MDA) production was reduced by increasing the citrate level. This effect was still present in plasma which was also anticoagulated with EDTA. Thrombin induced MDA production was considerably higher in EDTA than in citrate plasma. Citrate appears to inhibit aggregation as well as MDA synthesis. The latter effect does not seem to be solely caused by the effect of citrate on ionized calcium levels.

Blood Platelets↗

PubMedDate not supplied

Citrate activates tyrosinase from B-16 murine melanoma and human skin.

Citrate stimulates cresolase activity of tyrosinase from B-16 murine melanoma and human skin. Maximal stimulation by citrate was obtained at 2 mM, and stimulation was decreased at higher concentrations. Citrate stimulates tyrosinase not only from mammalian sources but also from mushroom. The stimulation was not due to reversal of inhibition of enzyme activity by excess tyrosine. On rapid decrease in pH of the enzyme solution from 6.8 to 5.0-5.2, the enzyme is no longer inhibited by excess tyrosine even when its activity was assayed at pH 6.8. Citrate also stimulates this form of enzyme. However, the stimulation is more at acidic pH than at pH 6.8. At higher concentrations of citrate the stimulatory effect decreases at both pH 5.0 and pH 6.8. Inhibition of this enzyme occurs at higher concentrations (22 mM) at pH 6.8. The physiological role of stimulation of cresolase activity of tyrosinase by citrate is yet to be unravelled.

Animals↗

PubMed1977

Citrate, a specific substrate for the isolation of Clostridium sphenoides.

With a medium containing citrate as the carbon and energy source, 10 clostridial strains were isolated from various mud samples. Characterization of these strains revealed that they all belonged to the same species, Clostridium sphenoides. Strains of this organism obtained from culture collections were also able to grow citrate, whereas 15 other clostridial species tested were not. Citrate was fermented by C. sphenoides to acetate, ethanol, carbon dioxide, and hydrogen. Experiments with stereospecifically 14C-labeled citrate indicated that citrate lyase was involved in citrate degradation.

Acetates↗

PubMed1971

Effects of citrate on the composition and metabolism of Lactobacillus casei.

Lactobacillus casei ATCC 393 converted small amounts of citrate to diacetyl, other volatile compounds, and lipids. Citrate was accumulated passively by the organism. The presence of citrate in the growth medium decreased the uptake of acetate and its conversion to cellular lipids. Cells grown in citrate media contained more protein per cell than did controls. This increased protein content was reflected mainly in the soluble fraction when cells were subjected to sonic lysis. Soluble fractions from cells cultured in the presence of citrate contained more total protein as well as more individual proteins than these fractions from control cells. The presence of citrate caused extensive flocculation and increased the susceptibility of cells to lysis.

Acetates↗

PubMed1975

Citrate uptake in membrane vesicles of Klebsiella aerogenes.

In whole cells of Klebsiella aerogenes grown anaerobically on citrate as sole carbon source, citrate uptake is followed by rapid catabolism of the substrate via the inducible citrate fermentation pathway. Membrane vesicles prepared from such cells take up citrate but do not catabolize it. Vesicles process d-lactate dehydrogenase and the Na+-requiring oxalacetate decarboxylase. Citrate is taken up in the presence of Na+, and other monovalent cations, such as NH4+, Rb+, Cs+, or K+, do not substitute for Na+. Li+ appears to act synergistically with Na+. Citrate uptake is inhibited by N-2, cyanide, azide, sulfhydryl reagents, dinitrophenol, fluorcitrate, and hydroxycitrate.

Anaerobiosis↗

PubMed1986

Inhibition of citric acid accumulation by manganese ions in Aspergillus niger mutants with reduced citrate control of phosphofructokinase.

Mutant strains of Aspergillus niger with reduced citrate control of carbohydrate catabolism (cic mutants) grow faster than the parent strain on media containing 5% (wt/vol) citrate. The mutants tolerated a higher intracellular citrate concentration than the parent strain. One mutant (cic-7/3) contained phosphofructokinase activity significantly less sensitive towards citrate than the enzyme from the parent strain. When this mutant was grown under citrate-accumulating conditions, acidogenesis was far less sensitive to inhibition by Mn2+ than in the parent strain. Some of the cic mutants also showed altered citrate inhibition of NADP-specific isocitrate dehydrogenase.

Aspergillus niger↗

PubMed1997

The reductive tricarboxylic acid cycle of carbon dioxide assimilation: initial studies and purification of ATP-citrate lyase from the green sulfur bacterium Chlorobium tepidum.

Carbon dioxide is fixed largely by the reductive tricarboxylic acid (RTCA) cycle in green sulfur bacteria. One of the key enzymes, ATP-citrate lyase, was purified to apparent homogeneity from the moderately thermophilic green sulfur bacterium Chlorobium tepidum. The molecular weight of the native enzyme was about 550,000, and the preponderance of evidence indicated that the protein is composed of identical subunits (Mr of approximately 135,000) which degraded to two major proteins with Mrs of approximately 65,000 and approximately 42,000. Western immunoblots and in vitro phosphorylation experiments indicated that these two species could have been the result of proteolysis by an endogenous protease, similar to what has been observed with mammalian, yeast, and mold ATP-citrate lyase. In addition to apparent structural similarities, the catalytic properties of C. tepidum ATP-citrate lyase showed marked similarities to the eukaryotic enzyme, with significant differences from other prokaryotic ATP-citrate lyases, including the enzyme from the closely related organism Chlorobium limicola. Phosphorylation of C. tepidum ATP-citrate lyase occurred, presumably on a histidine residue at the active site, similar to the case for the mammalian enzyme. In contrast to the situation observed for other prokaryotic ATP-citrate lyase enzymes, the C. tepidum enzyme was not able to replace ATP and GTP for activity or use Cu2+ to replace Mg2+ for enzyme activity. Given the apparent structural and catalytic similarities of the enzyme from C. tepidum and its eukaryotic counterpart, the C. tepidum system should serve as an excellent model for studies of the enzymology and regulation of this protein.

ATP Citrate (pro-S)-Lyase↗

PubMed1969

Induction and properties of the citrate transport system in Aerobacter aerogenes.

The mediated transport of citrate in Aerobacter aerogenes was studied. According to data obtained by examining the distribution of radioactive citrate at room temperature and at 0 C, a carrier system appears to be located on the membrane. The carrier system is inducible and very specific, not acting on the related compounds isocitrate and cis-aconitate. Induction required synthesis of both ribonucleic acid and protein as determined by starving auxotrophic mutants and by using specific inhibitors of protein synthesis. Citrate transport was inhibited by N-ethyl maleimide, dinitrofluorobenzene, and uranyl nitrate. A kinetic study of uranyl nitrate inhibition revealed that the inhibition of citrate transport was different from that of glucose penetration. Cyanide also discriminated citrate from glucose penetration inhibiting only the former. These last results suggested that energy is required for citrate penetration.

Azides↗

PubMed1990

Citrate synthase encoded by the CIT2 gene of Saccharomyces cerevisiae is peroxisomal.

The product of the CIT2 gene has the tripeptide SKL at its carboxyl terminus. This amino acid sequence has been shown to act as a peroxisomal targeting signal in mammalian cells. We examined the subcellular site of this extramitochondrial citrate synthase. Cells of Saccharomyces cerevisiae were grown on oleate medium to induce peroxisome proliferation. A fraction containing membrane-enclosed vesicles and organelles was analyzed by sedimentation on density gradients. In wild-type cells, the major peak of citrate synthase activity was recovered in the mitochondrial fraction, but a second peak of activity cosedimented with peroxisomes. The peroxisomal activity, but not the mitochondrial activity, was inhibited by incubation at pH 8.1, a characteristic of the extramitochondrial citrate synthase encoded by the CIT2 gene. In a strain in which the CIT1 gene encoding mitochondrial citrate synthase had been disrupted, the major peak of citrate synthase activity was peroxisomal, and all of the activity was sensitive to incubation at pH 8.1. Yeast cells bearing a cit2 disruption were unable to mobilize stored lipids and did not form stable peroxisomes in oleate. We conclude that citrate synthase encoded by CIT2 is peroxisomal and participates in the glyoxylate cycle.

Cell Fractionation↗

PubMed1980

A comparison of the citrate synthases of Escherichia coli and Acinetobacter anitratum.

Citrate synthase has been purified to homogeneity from a strain of the Gram-negative aerobic bacterium Acinetobacter anitratum in a form which retains its sensitivity to the allosteric inhibitor NADH. In subunit size, amino acid composition, and antigenic reactivity the enzyme shows a marked structural resemblance to the citrate synthase of the Gram-negative facultative anaerobe Escherichia coli. Whereas the E. coli enzyme is subject to a strong, hyperbolic inhibition by NADH (Hill's number n = 1.0, Ki = 2 microM), the A. anitratum enzyme shows a weak, sigmoid response (n = 1.6, I0.5 = 140 microM) to this nucleotide. With E. coli, NADH inhibition is competitive with acetyl-CoA, and noncompetitive with oxaloacetate; with A. anitratum, NADH is noncompetitive with both substrates. Acinetobacter anitratum citrate synthase shows hyperbolic saturation with acetyl-CoA (n = 1.8). The finding of Weitzman and Jones (Nature (London) 219, 270 (1968) that NADH inhibition of the enzyme from Acinetobacter spp. is reversible by AMP, while that from E. coli is not, is explained by the much greater affinity of the E. coli enzyme for NADH. Unlike E. coli citrate synthase, the A. anitratum enzyme does not react with the sulfhydryl reagent 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) in the absence of denaturation. With a second sulfhydryl reagent, 4,4'-dithiodipyridine (4,4'-PDS), the A. anitratum enzyme reacts with 1 equiv. of subunit; this modification induces a partial activity loss (attributable to a arise in the Km for acetyl-CoA) and an increase in the sensitivity to NADH. With the E. coli enzyme, 4,4'-PDS causes complete inactivation. Acinetobacter anitratum citrate synthase is much more resistant to urea denaturation than the E. coli enzyme is; the resistance of both enzymes to urea is greatly improved in the presence of 1 M KCl. It is suggested that the amino acid sequences of the subunits of the citrate synthases of these two bacteria are about 90% homologous, and that the 10% differences are in key residues, perhaps largely in the subunit contact regions, which account for the differences in allosteric properties.

Acinetobacter↗

PubMed1985

Transport of citrate across renal brush border membrane: effects of dietary acid and alkali loading.

Dietary acid or alkali loading was given to rats by providing 150 mM NH4Cl or 150 mM NaHCO3 in place of drinking water for 6 days; control animals received 150 mM NaCl. After 6 days, the citrate clearance was 0.04 +/- 0.01 ml/min (mean +/- SE) in the acid-loaded group, 0.9 +/- 0.1 ml/min in the control group, and 2.5 +/- 0.2 ml/min in the alkali-loaded group. At the end of the experiment, the rats were killed, and the Na+ gradient-dependent (Nao+ greater than Nai+) citrate uptake (pmol/mg protein) was measured in brush border membrane (BBM) vesicles prepared from each group. At 0.3 min, the [14C]citrate uptake was 198 +/- 8 pmol/mg protein (mean +/- SE) in the acid-loaded group, 94 +/- 16 pmol/mg protein in the control group, and 94 +/- 13 pmol/mg protein in the alkali-loaded group. The rate of Na+-independent (NaCl in medium replaced by KCl) [14C]-citrate uptake by BBM vesicles was the same for acid-loaded, control, and alkali-loaded animals. Thus, the increased capacity of the proximal tubular BBM to transport citrate from the tubular lumen into the cell interior may be an important factor that contributes to decreased urinary citrate in the presence of metabolic acidosis induced by chronic dietary acid loading.

Acid-Base Equilibrium↗

PubMed1988

Complementary role of citrate and bicarbonate excretion in acid-base balance in the rat.

Studies were performed to evaluate whether alterations in the excretion of citrate, a metabolic precursor of bicarbonate, play a quantitatively important role in acid-base balance during bicarbonate feeding in the rat. Potassium depletion (K-DEPL), chloride depletion (Cl-DEPL), or potassium plus chloride depletion (KCl-DEPL) was produced by eliminating potassium, chloride, or potassium chloride from the diet. After 3 days of depletion, sodium bicarbonate (4,000 mueq/24 h) was added to the diet for 7 days. In all groups plasma bicarbonate concentration increased minimally during bicarbonate administration and was similar to normal controls receiving bicarbonate. In K-DEPL, citrate excretion was less than normal but bicarbonate excretion was greater than normal. In Cl-DEPL, bicarbonate excretion was less than normal but citrate excretion was greater than normal. In KCl-DEPL, bicarbonate and citrate excretion were similar to normal. Sodium bicarbonate was also administered to K-DEPL and KCl-DEPL rats in which plasma bicarbonate concentration averaged 32.9 meq/1. The reciprocal relationship between citrate and bicarbonate excretion was not altered by the profound metabolic alkalosis. Again, plasma bicarbonate concentration changed little with sodium bicarbonate administration. These studies suggest that the ability to excrete a base load remains intact despite potassium or chloride depletion or metabolic alkalosis. Complementary alterations of citrate and bicarbonate excretion play an important role in acid-base balance under these conditions.

Acid-Base Equilibrium↗

PubMed1979

Leg and splanchnic arteriovenous differences of plasma citrate in exercising man.

Arteriovenous concentration differences of plasma citrate, glucose, lactate, pyruvate, free fatty acids, acetoacetate, and 3-hydroxybutyrate were determined across the leg and the splanchnic vascular bed in six healthy subjects in postabsorptive state, during 30 min of exercise (60--70% work load) and 65 min of recovery. A release of citrate across the leg and an uptake across the splanchnic vascular bed were found. Citrate arterial-femoral venous difference at rest, -19 +/- 2 mumol/l was abolished after 5 min of exercise and rebuilt during continuous work to reach peak value, -30 +/- 3 mumol/l at 20 min recovery. During exercise increasing negative arterial-femoral venous citrate differences were inversely related to fractional glucose extraction across the leg. Arterial-hepatic venous citrate difference at rest, 10 +/- 2 mumol/l, increased twofold during recovery. The results agree with the concept that a citrate inhibition of phosphofructokinase may be of regulatory importance for muscular glycolysis and glucose uptake as well as for hepatic glycolysis and gluconeogenesis in man during exercise.

Adult↗

PubMed2005

Regional citrate anticoagulation in continuous hemodialysis--acid-base and electrolyte balance at an increased dose of dialysis.

BACKGROUND: Citrate anticoagulation is an excellent alternative to heparin anticoagulation for patients at high risk of bleeding requiring continuous renal replacement therapy. However, citrate anticoagulation has some potential adverse effects such as metabolic alkalosis and acidosis, hypernatremia, hypo- and hypercalcemia. Thus, most citrate anticoagulation protocols use specially designed dialysis fluids to compensate for most of these disarrangements. This study aimed at establishing a citrate anticoagulation protocol designed for a dialysate flow rate of about 2 l/h. METHODS: Based on theoretical considerations we composed a dialysis fluid suitable for a 2 l/h dialysis flow rate. The dialysate contained 133 mmol/l sodium, 2 mmol/l potassium, 1.1 mmol/l magnesium, 25 mmol/l lactate, and 112.2 mmol/l chloride. RESULTS: Twenty-three patients were included in the study. During the treatments minor flow rate adaptations were needed and the treatments were well tolerated. Filter life was appropriate (51.3 +/- 24.6 h). Thirteen patients developed a mild metabolic alkalosis (pH > 7.45 plus BE > +3) which was easily counteracted by increasing the dialysis fluid flow (by increments of 500 ml). Acid-base values returned to normal within 24 h after increasing the dialysate flow. The maximum dialysate flow was 3,000 ml/h. Hypernatremia and hypocalcemia were not observed. The systemic ionized calcium concentration was successfully controlled by adjustments of a continuous calcium infusion made with respect to the results of 6-hourly measurements. CONCLUSION: The analyzed citrate anticoagulation protocol was well tolerated and filter lifetime was appropriate. Regional anticoagulation with trisodium citrate in combination with a customized calcium-free dialysate is a safe and effective alternative to a heparin-based anticoagulation regimen.

Acute Kidney Injury↗

PubMed2006

Excess casein in the diet is not the unique cause of low-grade metabolic acidosis: role of a deficit in potassium citrate in a rat model.

This study examined the effects of a dietary model of protein excess and K anion salt deficit on the occurrence of metabolic acidosis in rat. Rats were adapted to diets containing either 13 or 26% casein, together with mineral imbalance, through lowering K/increasing sodium/omitting alkalinizing anions. For each protein level, a group of rats was supplemented with K citrate. Dietary K citrate resulted in neutral urinary pH, whatever the protein level. Urea excretion was higher in rats adapted to 26% casein than 13% casein diets, but K citrate enhanced this excretion and suppressed ammonium elimination. No citraturia could be observed in acidotic rats, whereas K citrate greatly stimulated citraturia and 2-ketoglutarate excretion. In conclusion, low-grade metabolic acidosis can occur with a moderate protein level in the diet. K citrate was apparently less effective in rats adapted to the 26% casein level than in those adapted to the 13% casein level with regard to magnesium, citrate and 2-ketoglutarate concentrations in urine.

Acidosis↗

PubMedDate not supplied

Action of aldosterone on citrate synthase in cultured renal collecting duct cells.

Cultured renal collecting duct cells from neonatal rabbit kidney were used to examine the influence of aldosterone on enzymatic activity of citrate synthase during increase in Na+ transport. Control epithelia showed citrate synthase activity of 71 +/- 3 mU/mg protein (n = 28), while after aldosterone treatment citrate synthase activity was significantly increased to 79 +/- 6 mU/mg at 1 h (n = 5), to 88 +/- 6 mU/mg at 2 h (n = 6) and to 93 +/- 8 mU/mg protein at 3 h (n = 5). Citrate synthase activity subsequently decreased to basal values. Spironolactone fully blocked the aldosterone-induced increase in citrate synthase activity. The time course of enzyme stimulation after aldosterone administration indicates that the hormone activates citrate synthase during the physiological early response phase.

Adenosine Triphosphate↗