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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↗

PubMed1975

Citrate synthesis by lymphocytes.

The important role of lymphocytes in humoral and cell-mediated immunity indicates that they need a readily available intracellular source of energy. Here, we demonstrate that these cells contain enzymes involved in citrate formation. The citrate is oxidized through the tricarboxylic acid cycle to furnish energy. A newly devised, simple radiometric method was used to determine the condensation of labeled acetate or acetyl CoA with oxaloacetate to form citrate. The de novo synthesized citrate was oxidized to pentabromoacetone, and radioactivity of the resulting CO2 was directly related to the amount of citrate synthesized. Both lymphocytes from chronic lymphatic leukemia patients and cultured lymphoblasts possess this active citrate-synthesizing apparatus, although the lymphoblasts appeared to have a considerably higher activity, perhaps because they are larger.

Acetates↗

PubMed2001

The effects of sodium citrate ingestion on 3,000-meter time-trial performance.

The effect sodium citrate ingestion had on 3,000-m running performance was examined. Nine elite multidisciplinary athletes (7 men and 2 women, age 27.8 +/- 4.7 years, height 176 +/- 11 cm, mass 70.9 +/- 8.7 kg) completed two 3,000-m trials. The trials were double-blind and randomly assigned for sodium citrate (0.5 g x kg(-1) body mass) and for sodium (NaCl, 0.1 g x kg(-1) body mass). Split times, heart rate (HR), and 3,000-m completion times were measured. Blood samples were collected preingestion, pre-exercise, postexercise, and 10 minutes postexercise and analyzed for lactate concentration. Blood lactate (LA) was significantly higher (p < 0.05) for the sodium citrate trial, both postexercise and 10 minutes postexercise. No significant differences (p > 0.05) in HR were observed between trials. Performance time was significantly faster (p < 0.05) for the sodium citrate trial (610.9 +/- 36.6 seconds) compared with the placebo trial (621.6 +/- 31.4 seconds). Sodium citrate ingestion improved 3,000-m running performance in elite multidisciplinary athletes; however, the high potential for gastrointestinal distress likely precludes the use of sodium citrate as an ergogenic aid among athletes.

Adult↗

PubMed1987

Quantitation of the interaction between citrate synthase and malate dehydrogenase.

Formation of a bienzyme complex of pig heart mitochondrial malate dehydrogenase and citrate synthase in a buffered system is demonstrated by means of a covalently attached fluorescent probe to citrate synthase. Assuming 1:1 stoichiometry of the enzymes in the complex, an apparent dissociation constant of 10(-6) M was calculated from fluorescence anisotropy measurements. The effect of various metabolites on the interaction was tested. NAD+, oxalacetate, citrate, ATP, and L(-)- or D(+)-malate had no effect on the association of the two enzymes, whereas alpha-ketoglutarate increased and NADH decreased it. The interaction of mitochondrial citrate synthase with cytosolic malate dehydrogenase was found to be much weaker, whereas interaction of citrate synthase with another cytosolic enzyme, aldolase, could not be detected. In kinetic experiments, the activation of malate dehydrogenase by citrate synthase was observed. The effect of pyridine nucleotides and alpha-ketoglutarate is discussed in relation to the direction of the metabolic flow of oxalacetate.

Adenosine Triphosphate↗

PubMedDate not supplied

[Citrate metabolism during the consolidation of experimental fractures].

Simulation of reparative osteogenesis in diaphysis fracture of rat femur showed that liver tissue citrate synthase was a key enzyme in metabolism of citrate under conditions of organic matrix development in regenerating tissue. The liver enzyme as well as the callus citrate synthase were responsible for high rate of lipogenesis (activation of ATP-citrate lyase) and for an increase in content of citric acid within the initial period of consolidation. At the late steps of reparation callus citrate synthase, involved in citrate metabolism, promoted activation of energy-dependent reactions of calcification (stimulation of NAD-isocitrate dehydrogenase) and determined the dynamics of the metabolite concentration.

Animals↗

PubMed1995

The effects of sodium bicarbonate and sodium citrate on 600 m running time of trained females.

The effects of sodium bicarbonate and sodium citrate ingestion on 600 m running performance were assessed in 11 female track athletes and four trained female non-athletes. The subjects ingested either sodium bicarbonate (NaHCO3), sodium citrate or placebo approximately 2.5 hrs prior to the test runs in doses of 0.3 g/kg body weight in a double blind cross over design. Prior to and after exercise NaHCO3, H+, and lactate (HLa) concentrations were measured and running times were recorded. Pre- and post-experiment baseline testings were also performed. Data analysis was conducted using a Manova Repeated Measures design and dependent "t"-test. Although differences in running times were found 121.5 s, 119.9 s, 120.4 s in bicarbonate, citrate and placebo treatments respectively, they were not significant. The pH and concentrations of NaHCO3 were significantly elevated prior to and after the exercise when alkalinizing agents were ingested (p < 0.001). In bicarbonate treatment, prior to exercise pH was 7.40 and [NaHCO3] was 28.4 mEq/l, and after the exercise pH was 7.14 and [NaHCO3] was 17.9 mEq/l. In citrate treatment, prior to exercise pH was 7.40 and [NaHCO3] was 27.1 mEq/l, and after the exercise pH was 7.13 and [NaHCO3] was 16.6 mEq/l. There were no significant differences among the pre-exercise (2.3 mmol/l, 2.1 mmol/l, 2.2 mmol/l in bicarbonate, citrate and placebo treatments respectively) and after-exercise (11.8 mmol/l, 11.9 mmol/l, 11.0 mmol/l bicarbonate, citrate and placebo, respectively) HLa concentrations. This study demonstrated that, although alkali ingestion resulted in significant shifts in the blood acid-base balance, it failed to affect the 600 m running performance.

Acid-Base Imbalance↗

PubMed1999

Brief ex vivo perfusion with heparinized and/or citrated whole blood enhances tolerance of free muscle flaps to prolonged ischemia.

This study investigated the use of heparinized and/or citrated whole blood as a perfusate for enhancing muscle tolerance to warm ischemia. Unilateral cutaneous trunci muscle flaps were harvested from Sprague-Dawley rats and stored for 10 hr at 22-24 degrees C prior to transplantation to the groin. One group served as a non-perfused control. In three experimental groups, the flaps were hand-perfused ex vivo with 1.0 ml of heparinized, citrated, or heparinized and citrated autogenous whole blood at physiological pressures. Perfusion was administered over a 10-min period 5 hr into the ischemic period. Flaps were revascularized on the femoral vessels and then harvested 48 hr following revascularization. Tissue injury was assessed by calculation of flap weight change (indicator of tissue edema), histochemical evaluation of muscle dehydrogenase activity (nitroblue tetrazolium assay), and light microscopy. All perfused groups had significantly higher muscle dehydrogenase activity compared with non-perfused controls (P < 0.005). Perfusion with combined heparin-citrated blood was significantly more protective than perfusion with either anticoagulant alone (P < 0.025). The only statistically significant reduction in percent flap edema was seen in the combined heparin-citrate perfusion of flaps compared with nonperfused controls (P < 0.05). Histologic evaluation confirmed a reduction in tissue edema in the perfused flaps. We conclude that mid-ischemic perfusion with heparinized and/or citrated blood limits the deleterious effects of extended warm ischemia.

Analysis of Variance↗

PubMed1988

Dose dependency of calcium absorption: a comparison of calcium carbonate and calcium citrate.

Calcium supplementation is recommended as a prophylaxis against bone loss. This study was performed to determine the dose dependency of calcium absorption in an attempt to derive an optimum dose schedule. Using the well-described oral calcium load technique, we measured the calcium absorption from three different calcium doses (0.5, 1.0, and 2.0 g) of both calcium carbonate and calcium citrate administered to 21 normal subjects (4 men and 17 women, 22-60 years). Nine subjects underwent two additional loads with 0.2 g of elemental calcium as calcium carbonate and as calcium citrate. The intestinal calcium absorption from calcium carbonate and calcium citrate was estimated from the rise in urinary calcium following oral ingestion of the respective calcium salt. The increment in urinary calcium post-load, reflective of intestinal calcium absorption, rose rapidly from 0 to 0.5 g calcium loads with only slight subsequent increases from the 0.5 g to 2.0 g calcium doses. Thus, results indicate that 0.5 g of calcium is the optimum dose of either calcium salt. Moreover, the increment in urinary calcium post-load was higher from calcium citrate than from calcium carbonate at all four dosage levels. The increment in urinary calcium (during the second 2 hr) following calcium citrate load (0.5 g calcium) was 0.104 +/- 0.096 mg/dl glomerular filtrate (GF), which was higher than that of 0.091 +/- 0.068 mg/dl GF obtained from 2.0 g calcium as calcium carbonate. These results confirm the superior calcium bioavailability from calcium citrate as compared with calcium carbonate.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1991

Concepts of citrate production and secretion by prostate: 2. Hormonal relationships in normal and neoplastic prostate.

A unique and major function of prostate secretory epithelial cells is to synthesize, accumulate, and secrete extraordinarily high levels of citrate. This function is regulated by testosterone and by prolactin. Concepts of the mechanisms of hormonal regulation are presented. The relationship of testosterone and prolactin to the origin and homologies of different prostate cell lines is described. The metabolic differentiation of citrate and non-citrate producing prostate secretory epithelial cells is discussed. Concepts of the pathogenesis of prostatic neoplasms are presented based on hormonal, metabolic, and homologous relationships associated with citrate production. Characterization of normal and neoplastic secretory epithelial cells by their citrate function is emphasized. The urgency and necessity for research relating to all aspects of prostate citrate production in normal and pathological prostate are emphasized.

Animals↗

PubMed1994

Glutamine catabolism by heart muscle: regulation of phosphate-activated glutaminase by ATP, citrate, and chloride.

Production of glutamate from glutamine by rat heart mitochondria was stimulated by citrate and ATP in a dose-dependent manner. Citrate required phosphate for manifestation of its stimulatory action, whereas ATP enhanced glutaminase activity with and without phosphate. At low concentrations (1-50 mM) ATP was more potent than citrate, whereas the opposite was true at high (50-150 mM) levels of these anions. Both citrate and ATP decreased the concentration of phosphate required for half-maximal stimulation of glutamate production (EC50) and reduced the value of the Hill coefficient. Phosphate lowered the EC50 for ATP. Chloride and other anions of chaotropic series inhibited glutamine catabolism, most likely by causing depolymerization of the enzyme. Rupture of mitochondrial membranes by freeze-thawing decreased the responsiveness of glutaminase to phosphate, ATP, and especially to citrate but it did not alter the inhibition of the enzyme by chaotropic anions. It is concluded that phosphate, ATP, and citrate act in concert to modulate glutaminase activity in heart in vivo. Chloride, which exhibits a small inhibitory effect at a concentration normally present in cardiac muscle, may assume a greater regulatory role in situations accompanied by a rise in the internal level of this anion.

Adenosine Triphosphate↗

PubMed1977

The occurrence of Pseudomonas spp. in surface water and in tap water as determined on citrate media.

Citrate-utilizing bacteria were counted in 289 samples of tap water derived from either surface water or ground water and in 32 samples of raw or partially treated surface water by using media containing ferric ammonium citrate as the carbon and energy source. The citrate-utilizing bacteria constituted only small minorities of the colony counts on Lab-Lemco agar at 25 C in both tap water and surface water. A total of 1071 isolates were obtained, of which 979 were able to utilize citrate. Characterization of the citrate-utilizing isolates revealed that 90% of these bacteria were arginine dihydrolase-positive and belonged to the genera Pseudomonas (84.3%) and Aeromonas (5.7%). The genus Pseudomonas was represented by fluorescent pseudomonads (66.3%), non-fluorescent glucose-utilizing pseudomonads (12.1%) and P. alcaligenes (5.9%). None of the isolates was identified as P. aeruginosa. It is suggested that the pseudomonads and the aeromonads are not adapted to low substrate concentrations. Enumeration of the citrate-utilizing bacteria in tap water therefore may give information on the efficiency of water treatment techniques as regards the substrate removal.

Aeromonas↗

PubMed1996

Is citrate an inhibitor of calcium oxalate crystal growth in high concentrations of urine?

The effect of citrate on calcium oxalate (CaOx) crystal growth was studied in a system in which series of samples containing [45Ca]calcium chloride were brought to different levels of supersaturation with various concentrations of oxalate. The crystallization was assessed by measuring the amount of isotope remaining in solution 30 min after the addition of CaOx seed crystals to samples containing citrate in concentrations corresponding to those in final urine. The experiments were carried out both in pure salt solutions and in solutions with dialysed urine. Increased concentrations of citrate resulted in a reduced crystallization of CaOx in both the presence and absence of dialysed urine, but with the lowest rate of crystallization in the samples containing urine. The increased concentration of 45Ca remaining in solution reflected a reduced crystallization, which could possibly be explained both by a reduced supersaturation and by an increased inhibition of CaOx crystal growth. The direct effects of citrate on CaOx crystal growth were assessed by calculating the ion-activity product of CaOx (APCaOx) at corresponding degrees of crystallization. The APCaOx recorded at a 30% reduction of the amount of isotope in solution increased with increasing concentrations of citrate between 1.0 and 1.5 mmol/l samples both with and without dialysed urine. These findings indicate that citrate has a weak direct inhibitory effect on CaOx crystal growth, which adds to the reduced growth rate brought about by urinary macromolecules and a decreased supersaturation.

Antacids↗

PubMed1996

The bioavailability of 26Al-labelled aluminium citrate and aluminium hydroxide in volunteers.

A study was undertaken to determine the fraction of ingested aluminium taken up by two male volunteers, following their ingestion of either aluminium citrate or aluminium hydroxide. In addition, the effects of simultaneous citrate ingestion on the gastrointestinal absorption of aluminium from its hydroxide was studied. Volunteers received three oral doses of 26Al-labelled aluminium compound in water. The doses were administered directly into the stomach using a paediatric feeding tube. Blood samples were collected from the volunteers at 1, 4 and 24 h after administration, and their daily output of urine and faeces was collected for 6 days. These samples were analysed for their 26Al content using either coincidence gamma-counting or accelerator mass spectrometry. The uptake of aluminium was greatest following its administration in the citrate form and was least following intake as the aluminium hydroxide suspension. The co-administration of citrate, with the aluminium hydroxide suspension, was found to enhance the levels of 26Al uptake in both volunteers. Using a urinary excretion factor based on the results of previous studies, the fractional aluminium uptake from each of the species was calculated: aluminium citrate, 5.23 x 10(-3); aluminium hydroxide, 1.04 x 10(-4); aluminium hydroxide with citrate, 1.36 x 10(-3).

Adult↗

PubMed1995

Comparison of technetium-99m methoxyisobutylisonitrile and gallium-67 citrate scanning in the assessment of lymphomas.

The aim of this study was to compare the value of scintigraphy using technetium-99m methoxyisobutylisonitrile (MIBI) with that of scintigraphy using gallium-67 citrate in the assessment of Hodgkin's disease and non-Hodgkin's lymphoma and to relate these results with those of CT scan and MRI. Fifty-eight patients were included either for a follow-up examination or for monitoring of their treatment. Twenty-three residual masses were studied. A whole-body scan was performed, followed by single-photon emission computed tomography (SPET) 20 min after injection of 740 MBq of 99mTc-MIBI and 72 h after injection of 185 MBq of 67Ga citrate. The overall sensitivity of 99mTc-MIBI and 67Ga citrate was 71% and 68%, respectively, and the overall specificity was 76% and 44%, respectively. For residual masses, the sensitivity was 44% with both tracers and the specificity was 80% with 99mTc-MIBI and 53% with 67Ga citrate. The positive predictive values were 85% and 68% and the negative predictive values were 59% and 44%, respectively. The signal-to-background ratio was 1.5 for 99mTc-MIBI and 2 for 67Ga citrate. At present, 99mTc-MIBI cannot replace 67Ga citrate in the assessment of lymphomas.

Adult↗

PubMed1993

Management of primary hyperoxaluria: efficacy of oral citrate administration.

The prognosis of primary hyperoxaluria (PH) is not only related to endogenous oxalate production and the response (if any) to pyridoxine (in type I), but is greatly influenced by extrarenal factors like dehydration. The earlier the diagnosis of PH, the better the chances of improving the prognosis in individual patients. Measures to enhance the solubility of calcium oxalate are important. Besides ensuring at all times a generous fluid intake (> 2 l/m2), administration of alkali citrate (0.15 g/kg), which has not been advocated so far in PH, appears very promising. We studied the effect of sodium citrate in six patients with PH. Mean urinary citrate excretion (mmol/day per 1.73 m2) without oral citrate was very low (0.57) and rose to 2.49 with citrate administration. This was accompanied by a significant decrease in the calcium oxalate saturation (calculated by equil 2) from 11.7 to 6.9 (P < 0.05). Treatment in five patients over 10-36 months resulted in improved (1) or stabilized (4) renal function and reduced passage of stones. Additional measures include restriction of salt and of oxalate-rich food. We conclude that long-term administration of alkali citrate is beneficial in patients with PH.

Administration, Oral↗

PubMed1985

Statistical evidence for the relation between citrate and carbonate in human cortical bone.

Bone specimens from the anterior iliac crest were collected post-mortem from 128 subjects whose death had been primarily caused by acute coronary disease or accidents. The cortical bone was separated and used for the following determinations: citrate by an enzymatic method, carbon dioxide by microdiffusion, chloride and phosphorus by spectrophotometry, fluoride by the ion-selective electrode technique, and Ca, Mg, Zn by atomic absorption spectrophotometry. The citrate concentration (+/- SD) was 10.9 +/- 3.1 mg/g (dry weight) and was not age-dependent. A statistically significant negative correlation was obtained between citrate and carbon dioxide, however, which was confirmed by regression analysis. The only statistically significant differences in carbon dioxide and fluoride concentrations between three citrate groups were obtained between the lowest group (3.2-8.7 mg/g) and the highest (13.1-16.8 mg/g). In conclusion an inverse relationship may suggest either an effect of citrate on the binding of carbonate to apatite structures, or that the carbonate concentration is dependent to a slight degree on citrate metabolism.

Adult↗

PubMed2005

Long-term potassium citrate therapy and bone mineral density in idiopathic calcium stone formers.

Several authors have described an association between idiopathic calcium (Ca) stone disease and bone mass reduction. Hypocitraturia is a frequent feature of urolithiasis, and alkaline citrate has been recommended as one of the choice treatments in this disease. Some evidence exists as to the positive effect of potassium (K) citrate therapy on bone mass. The aim of this work was the longitudinal evaluation of bone mineral density (BMD) changes in a group of Ca oxalate stone formers treated with K citrate for two years. Enrolled patients were 120; 109 subjects completed the study (51 males and 58 females). A metabolic study and distal radius BMD measurements were conducted both at baseline (BAS) and at the end of the study (END). BMD (0.451 +/- 0.081 vs 0.490 +/- 0.080 g/cm2), T-score (-1.43 +/- 1.02 vs -0.90 +/- 1.04), net gastrointestinal alkali absorption (40.37 +/- 50.57 vs 61.26 +/- 42.26 mEq/day), urinary citrate (2.53 +/- 1.15 vs 3.10 +/- 1.44 mmol/day) and K (58.93 +/- 22.28 vs 65.45 +/- 23.97 mmol/day) excretion significantly increased from BAS to END. Urinary Ca excretion remained unchanged from BAS to END (5.16 +/- 2.74 vs 5.57 +/- 2.85 mmol/ day). Our results indicate that long-term treatment with K citrate increases forearm BMD in idiopathic Ca stone formers. It seems probable that the alkali load provided by this drug reduces bone resorption by a buffering of the endogenous acid production. K citrate appears to be a further therapeutic opportunity for the management of osteoporosis in Ca stone formers.

Absorptiometry, Photon↗

PubMed2002

Impact of the Mg(2+)-citrate transporter CitM on heavy metal toxicity in Bacillus subtilis.

Bacillus subtilis possesses a secondary transporter, CitM, that is specific for the complex of citrate and Mg(2+) but is also capable of transporting citrate in complex with the heavy metal ions Zn(2+), Ni(2+) and Co(2+). We report on the impact of CitM activity on the toxicity of Zn(2+), Ni(2+) and Co(2+) in B. subtilis. In a citM deletion mutant or under conditions in which CitM is not expressed, the toxic effects of the metals were reduced by the presence of citrate in the medium. In contrast, the presence of citrate dramatically enhanced toxicity when the Mg(2+)-citrate transporter was present in the membrane. It is demonstrated that the complex of Ni(2+) and citrate is transported into the cell and that the uptake is responsible for the enhanced toxicity. At toxic concentrations of the metal ions, the cultures adapted by developing tolerance against these ions. Tolerant cells isolated by exposure to one of the metal ions remained tolerant after growth in the absence of toxic metal ions and were cross-tolerant against the other two toxic ions. Tolerant strains were shown to contain point mutations in the citM gene, which resulted in premature termination of translation.

Adaptation, Physiological↗