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At least 91 records · Page 5Linked to original sources
PubMed2006

Citrate-release-mediated aluminum resistance is coupled to the inducible expression of mitochondrial citrate synthase gene in Paraserianthes falcataria.

Aluminum (Al) resistance in some leguminous plants is achieved by enhanced citrate release from roots. Enhancement requires several hours for complete activation and is postulated to involve Al-responsive genes or components. We examined the mechanism of Al-induced citrate release by studying the relationship between citrate release and expression of the mitochondrial citrate synthase (mCS) gene in three leguminous trees. Root elongation in Leucaena leucocephala (Lam.) de Wit was arrested within 24 h by 30 microM Al, whereas root elongation in Paraserianthes falcataria (L.) Neilson and Acacia mangium Willd. was inhibited < 50% by a 48-h treatment with 100 microM Al in calcium chloride solution. Roots of P. falcataria and A. mangium maintained enhanced release and accumulation of citrate for at least 28 days in response to Al treatment. Aluminum increased the accumulation of mCS transcripts in P. falcataria roots, but not in L. leucocephala roots, and thus up-regulation decreased following removal of Al. Lanthanum did not alter the expression level of mCS. Aluminum increased mCS activity concomitantly with enhanced mCS gene expression in P. falcataria, whereas it did not affect mCS activity in L. leucocephala. Aluminum content in root apices of P. falcataria was increased by cycloheximide, supporting the idea that de novo synthesis of proteins is a prerequisite for Al resistance. Our findings suggest that Al-inducible expression of mCS coupled with enhanced citrate release mediates Al resistance in P. falcataria.

Aluminum↗
PubMed1989

Bioavailability of citrate from two different preparations of potassium citrate.

The bioavailability of citrate from two different preparations of potassium citrate was examined in eighteen normal volunteers during three phases of study. After stabilization on a constant metabolic diet, subjects took a single dose of placebo, "slow-release" potassium citrate tablets (60 meq) or rapid-release liquid potassium citrate preparation (60 meq). Timed urine specimens were collected for 24 hours and analyzed for citrate, potassium, and pH. Similar biochemical findings were observed following administration of the two different preparations with the onset and decline of changes being slightly more rapid for the liquid potassium citrate than the tablet preparation. These equivalent bioavailability data indicate that the liquid preparation is a comparable therapeutic alternative to the tablet form.

Adult↗
PubMedDate not supplied

Metabolic engineering of a non-allosteric citrate synthase in an Escherichia coli citrate synthase mutant.

This study examined the organization of the Krebs tricarboxylic acid (TCA) cycle by metabolic engineering and high-resolution 13C NMR. The oxidation of [1,2,3-13C]propionate to glutamate via the TCA cycle was measured in wild-type (WT) and a citrate synthase mutant (CS-) strain of Escherichia coli transformed with allosteric E. coli citrate synthase (ECCS) or non-allosteric pig citrate synthase (PCS). The 13C fractional enrichment in glutamate C-2, C-3, and C-4 in ECCS and PCS were similar; although quantitative differences in total citrate synthase activity and total C-4 labeling of glutamate were observed in ECCS and PCS. Allosteric ECCS cells contained 10-fold less total enzyme activity than PCS but only 50% less total labeling in glutamate C-4 and equivalent doubling times. The observed spectra were mathematically fitted using an iterative procedure (TCACALC) and yielded an acetate/succinyl-CoA flux ratio of 10 for both ECCS and PCS, a result that is in agreement with the isotopomer analyses of the 13C spectra of cells presented with [3-13C]propionate or [2-13C]propionate. The results are consistent with the presence of an allosteric citrate synthase in ECCS and a non-allosteric citrate synthase in PCS. The former maintains TCA cycle flux via alternative propionate pathways activated by positive allosteric mechanisms and the latter via elevated enzyme levels.

Allosteric Regulation↗
PubMed1985

Acute oral alkali citrate load in healthy humans--response of blood and urinary citrate, mineral metabolism, and factors related to stone formation.

In ten healthy volunteers (male/female = 5/5) the effects of two doses (2.5 and 5.0 g) of orally ingested alkali citrate (AC) on serum citrate, variables of mineral metabolism in serum, the urinary excretion of citrate, sodium and minerals were studied and compared with the effects of an oral vehicle load. Also, phosphate crystalluria and the supersaturation of several stone forming phases in urine were evaluated under all loads. The data allow to conclude that 1) the rise in serum citrate may result from citrate absorbed intestinally under AC; 2) systemic metabolic alkalosis is not detectable with the chosen AC doses but may be reflected by the more alkaline urinary pH and a higher citrate excretion; 3) mineral metabolism, serum ionized calcium, parathormone, calcitonin and urinary cyclic AMP included, are more or less stable under acute loads of AC; 4) postprandial phosphate crystalluria is more pronounced with increasing AC, but despite this the direct correlation with the supersaturation of hydroxyapatite is progressively weakened with both doses AC suggesting that the inhibitory effects of this drug may dominate over its effects upon initiation of precipitation.

Adult↗
PubMed1997

Evaluation of 99mTc-citrate, 67Ga-citrate and 99mTc(V) dimercaptosuccinic acid for the scintigraphic visualization of acute appendicitis.

An experimental study was planned to evaluate 99mTc-citrate, 67Ga-citrate and 99mTc(V) dimercaptosuccinic acid (DMSA) as agents for the visualization of acute appendicitis. Appendiceal ligation was performed through a midline incision in 24 rabbits. Twenty-four hours later the animals were divided into three equal groups. The rabbits were injected through the aurical vein with 1 mCi (37 MBq) 99mTc-citrate in group I, 0.5 mCi (18.5 MBq) 67Ga-citrate in group II and 1 mCi (37 MBq) 99mTc(V) DMSA in group III. After 3 h, static images of the rabbits were obtained with a gamma camera. There were positive images in seven, six and five rabbits in groups I, II and III respectively. The image quality was better in group I than in the other groups. Also, the mean uptake in group I was significantly higher than those of other two groups (P < 0.05). There was no significant difference between groups II and III (P > 0.05). All rabbits had appendicitis confirmed histologically. In conclusion, these results show that 99mTc-citrate is preferable to 67Ga-citrate and 99mTc(V) DMSA for the differential diagnosis of acute abdominal inflammations such as appendicitis, because of higher concentration ratios, simple and rapid preparation, low cost, excretion mainly through the kidneys and fast blood clearance.

Acute Disease↗
PubMed1995

The visualization of pulmonary tuberculosis with Tc-99m (V) DMSA and Tc-99m citrate in comparison to Ga-67 citrate.

Two patients with active tuberculosis confirmed by chest radiography and positive sputum smears were included in this study to determine whether a Tc-99m labeled agent, such as DMSA or citrate could localize such lesions in comparison to Ga-67 citrate. Both patients had Tc-99m (V) DMSA, Tc-99m citrate, and Ga-67 citrate scanning at 1-day to 5-day intervals. Both patients had positive scan findings with all three radiopharmaceuticals. However, the quality of Tc-99m (V) DMSA scans was superior to Tc-99m citrate, which showed faint uptake. Tc-99m (V) DMSA may be a better alternative to Ga-67 citrate in the assessment of the activity and extent of tuberculosis.

Adult↗
PubMed1975

Studies on citrate metabolism in liver injuries. 2. Response of liver citrate to glucose load.

The effect of glucose load on the levels of blood glucose, serum non-esterified fatty acids (NEFA) and liver citrate was investigated in carbontetrachloride-intoxicated (injured) rats and compared with non-intoxicated controls. The citrate level in the liver from injured animals showed 15-fold of the value of the control. Glucose load on these animals caused gradual decrease in the citrate level, whereas similar administration to the control caused inverse results. The serum NEFA levels were lowered by glucose load in both of injured and control animals. The pattern of changes in the citrate level after glucose load in the liver from injured animals was similar to that in the muscle from the control, suggesting a similarity on citrate metabolism between the injured liver and the muscle. The possible mechanisms for these results were discussed in relation to the difference in citrate metabolism between the liver and the muscle.

Animals↗
PubMed2000

Manganese citrate chemistry: syntheses, spectroscopic studies, and structural characterizations of novel mononuclear, water-soluble manganese citrate complexes.

The first two mononuclear manganese citrate complexes, (NH4)4[MnII(C6H5O7)2] (1) and (NH4)5[MnIII(C6H4O7)2].2H2O (2) were synthesized in aqueous solutions near physiological pH values. They were isolated in their pure crystalline forms and characterized by elemental analyses and spectroscopic techniques, including UV/visible, electron paramagnetic resonance, Fourier transformed infrared, and magnetic susceptibility measurements. Compound 1 crystallizes in the monoclinic space group P2(1)/c, with a = 8.777(1) A, b = 13.656(3) A, c = 9.162(2) A, beta = 113.62(2) degrees, V = 1006.2(6) A3, and Z = 2. Compound 2 crystallizes in the triclinic space group P1, with a = 9.606(3) A, b = 9.914(3) A, c = 7.247(3) A, alpha = 91.05(1) degrees, beta = 105.60(1) degrees, gamma = 119.16(1) degrees, V = 571.3(3) A3, and Z = 1. The X-ray crystal structures of 1 and 2 revealed that, in both cases, the manganese ion is six-coordinate and is bound by two citrate ligands in a distorted octahedral fashion. In the case of complex 1, the citrate ion binds to Mn2+ as a triply deprotonated ligand, retaining the central carbon hydroxyl hydrogen, whereas, in the case of compound 2, the citrate ligand coordinates to Mn3+ as a fully deprotonated entity. Compound 2 contains water molecules of crystallization in the unit cell which, through extensive hydrogen-bonding interactions, bestow considerable stability upon the Mn(3+)-citrate assembly. There are significant contributions to the stabilities of the assembled lattices in 1 and 2 arising from the ammonium counterions neutralizing the high anionic charges of the complexes. The EPR spectra attest to the presence of paramagnetic Mn2+ and Mn3+ species in the solid state. Corroborative evidence is obtained from the magnetic susceptibility measurements in the range 5-300 K. Complexes 1 and 2 present clear cases of mononuclear manganese citrate species relevant to manganese speciation in biological media and potentially related to the beneficial as well as toxic effects of manganese on humans.

Journal Article↗
PubMed1976

[Behavior of some parameters of lipid and energy metabolism. 2. Activity of citrate synthase, ATP citrate lyase, fatty acid synthase, and glucose-6-phosphate dehydrogenase in liver of growing rats on diets differing in fat content].

In continuation of previous investigations, the authors studied the behaviour of the activities of certain enzymes (citrate synthase, adenosine triphosphate citrate lyase, fatty acid synthase and glucose-6-phosphate dehydrogenase) in the livers of growing rats on diets differing in fat content. A high-fat diet resulted in a reduction of the activities of fatty acid synthase, glucose-6-phosphate dehydrogenase and adenosine triphosphate citrate lyase, whereas the activity of citrate synthase increased, which is interpreted in the sense of an acceleration of the introduction of acetyl residues into the citrate cycle for the purpose of oxidative final degradation, and as a removal of acetyl CoA for the purpose of fatty acid synthesis.

ATP Citrate (pro-S)-Lyase↗
PubMed1992

Citrate and recurrent idiopathic calcium urolithiasis. A longitudinal pilot study on the metabolic effects of oral potassium citrate administered over the short-, medium- and long-term medication of male stone patients.

In idiopathic recurrent calcium urolithiasis (RCU) in men (n = 37) the metabolic effects of oral tripotassium citrate (PC) were investigated in a longitudinal field study. The patients were either normo- (n = 22) or hypocitraturic (n = 15). Laboratory examinations were performed before, and after 3, 6, and more than 12 months of medication. Acceptance of PC was poor, mainly because of the salty taste of the tablet preparation chosen, and a number of participants dropped out of the study. In the remaining participants, compliance was acceptable when evaluated on the basis of urinary potassium and undesired side effects did not occur. In the short term (up to 3 months), PC evoked compensated metabolic alkalosis (pH and citrate in urine increased; blood gases remained normal), a drop in urinary calcium, together with increasing oxaluria, hydroxyapatite supersaturation, and calcium phosphate crystalluria. In the long term (greater than 12 months) PC urinary pH and citrate "dissociated", in that pH returned to pretreatment baseline values, whereas citrate stayed at high levels. In normocitraturics but not in hypocitraturics, urinary urea and sodium increased with PC. Hypocitraturics appeared to be less sensitive to the effects of PC, as reflected by the relatively small rise in urinary pH and citrate, and they maintained higher mean levels of indicators of bone metabolism (osteocalcin, alkaline phosphatase, hydroxyproline) despite continuous administration of PC. It was concluded that although the PC tablet preparation was effective it may not be an ideal anti-stone drug treatment in the long term and that, especially in hypocitraturics, the intrinsic metabolic defect of RCU may not be sufficiently well controlled.

Acid-Base Equilibrium↗
PubMed1992

Citrate and recurrent idiopathic calcium urolithiasis. A longitudinal pilot study on the metabolic effects of oral potassium sodium citrate administered as short-, medium- and long-term to male stone patients.

In male patients with idiopathic recurrent calcium urolithiasis (RCU) the effects of oral potassium sodium citrate (PSC) on acid-base, citrate and mineral metabolism were investigated. There were 17 normocitraturic and 15 hypocitraturic patients. The examination time points in our clinical laboratory were prior to medication and after 3, 6 and over 12 months of medication. Urine collection periods were over 24 h, 2 h--after an overnight fast--3 h postprandially. Acceptance by the patients was poor, a large number refusing to take PSC for 12 months. Compliance of the patients continuing with the study was adequate as assessed by the urinary excretion of potassium and sodium. No unwanted side effects were observed. After 3 months of PSC medication a compensated metabolic alkalosis developed; in the urine calcium was decreased, while citrate, pH and oxalate were increased, as were hydroxyapatite supersaturation and calcium phosphate particles. After more than 12 months of PSC medication, citrate and pH tended toward the pretreatment baseline values, while hydroxyapatite supersaturation and calcium had already returned to pretreatment values. Despite ongoing PSC intake, patients with pre-existing hypocitraturia had lower urinary citrate than patients with previous normocitraturia, while the concomitant pH and hydroxyapatite supersaturation in the urine of the former remained at levels close to those of the latter. Under the influence of PSC, parathyroid gland function remained unchanged, but serum levels of bone alkaline phosphatase and osteocalcin were low, and urinary hydroxyproline was high.(ABSTRACT TRUNCATED AT 250 WORDS)

Acid-Base Equilibrium↗
PubMed2005

Mononuclear titanium(IV)-citrate complexes from aqueous solutions: pH-specific synthesis and structural and spectroscopic studies in relevance to aqueous titanium(IV)-citrate speciation.

Titanium is a metal frequently employed in a plethora of materials supporting medical applications. In an effort to comprehend the involvement of titanium in requisite biological interactions with physiological ligands, synthetic efforts were launched targeting aqueous soluble species of Ti(IV). To this end, aqueous reactions of TiCl(4) with citric acid afforded expediently, under pH-specific conditions, the colorless crystalline materials Na(6)[Ti(C(6)H(4.5)O(7))(2)(C(6)H(5)O(7))].16H(2)O (1) and Na(3)(NH(4))(3)[Ti(C(6)H(4.5)O(7))(2)(C(6)H(5)O(7))].9H(2)O (2). Complexes 1 and 2 were characterized by elemental analysis, FT-IR, (13)C-MAS solid state and solution NMR, cyclic voltammetry, and X-ray crystallography. 1 crystallizes in the triclinic space group P, with a = 15.511(9) A, b = 15.58(1) A, c = 9.848(5) A, alpha = 85.35(2) degrees, beta = 76.53(2) degrees, gamma = 61.97(2) degrees, V = 2042(2) A(3), and Z = 2. 2 crystallizes in the triclinic space group P, with a = 12.437(5) A, b = 12.440(5) A, c = 12.041(5) A, alpha = 83.08(2) degrees, beta = 81.43(2) degrees, gamma = 67.45(2) degrees, V = 1697(2) A(3), and Z = 2. The X-ray structures of 1 and 2 reveal the presence of a mononuclear complex, with Ti(IV) coordinated to three citrate ligands in a distorted octahedral geometry around Ti(IV). The citrates employ their central alkoxide and carboxylate groups to bind Ti(V), while the terminal carboxylates stay away from the Ti(IV)O(6) core. Worth noting in 1 and 2 is the similar mode of coordination but variable degree of protonation of the bound citrates, with the locus of (de)protonation being the noncoordinating terminal carboxylates. As a result, this work suggests the presence of a number of different Ti(IV)-citrate species of the same nuclearity and coordination geometry as a function of pH. This is consistent with the so far existing pool of mononuclear Ti(IV)-citrate species and provides a logical account of the aqueous speciation in the requisite binary system. Such information is vital in trying to delineate the interactions of soluble and bioavailable Ti(IV) forms promoting biological interactions in humans. To this end, chemical properties, structural attributes, and speciation links to potential ensuing biological effects are dwelled on.

Biological Availability↗
PubMed2004

Unprecedented oxo-titanium citrate complex precipitated from aqueous citrate solutions, exhibiting a novel bilayered Ti8O10 structural core.

Aqueous titanium citrate solutions were prepared from the reaction of citric acid with titanium 2-propoxide in a range of molar ratios. Solutions containing two or fewer citrates per titanium resulted in the slow crystallization of an insoluble titanium oxo-citrate complex. Single-crystal X-ray analysis identified the species as Ti(8)O(10)(citrate)(4)(H(2)O)(12).14H(2)O.3HOPr(i)(), crystallized in the tetragonal space group I4(1)/a, with a = 30.775(7) A, c = 14.528(7) A, V = 13 759(8) A(3), and Z = 8. The trianionic citrate ligands supply both carboxylate and alkoxide coordination and stabilize the structure using simultaneous chelating and bridging modes of attachment. The compound is a neutral species, exhibiting titanium in three contrasting environments. Laser Raman microscopy and (13)C CPMAS solid-state NMR data were consistent with those of the X-ray crystal structure. When exposed to air, the crystals rapidly lost water and became a powder. The dehydrated powder was noncrystalline to X-rays and insoluble, but (13)C NMR results demonstrated retention of the carboxylate linkages.

Citrates↗
PubMed1998

The role of ATP citrate-lyase in the metabolic regulation of plasma lipids. Hypolipidaemic effects of SB-204990, a lactone prodrug of the potent ATP citrate-lyase inhibitor SB-201076.

ATP citrate (pro-S)-lyase (EC 4.1.3.8), a cytosolic enzyme that generates acetyl-CoA for cholesterol and fatty acid synthesis de novo, is a potential target for hypolipidaemic intervention. Here we describe the biological effects of the inhibition of ATP citrate-lyase on lipid metabolism in Hep G2 cells, and plasma lipids in rats and dogs, by using SB-204990, the cell-penetrant gamma-lactone prodrug of the potent ATP citrate-lyase inhibitor SB-201076 (Ki=1 microM). Consistent with an important role of ATP citrate-lyase in the supply of acetyl-CoA units for lipid synthesis de novo, SB-204990 inhibited cholesterol synthesis and fatty acid synthesis in Hep G2 cells (dose-related inhibition of up to 91% and 82% respectively) and rats (76% and 39% respectively). SB-204990, when administered orally to rats, was absorbed into the systemic circulation; pharmacologically relevant concentrations of SB-201076 were recovered in the liver. When administered in the diet (0.05-0. 25%, w/w) for 1 week, SB-204990 caused a dose-related decrease in plasma cholesterol (by up to 46%) and triglyceride levels (by up to 80%) in rats. This hypolipidaemic effect could be explained, at least in part, by a decrease (up to 48%) in hepatic very-low-density lipoprotein (VLDL) production as measured by the accumulation of VLDL in plasma after injection of Triton WR-1339. SB-204990 (25 mg/kg per day) also decreased plasma cholesterol levels (by up to 23%) and triglyceride levels (by up to 38%) in the dog, preferentially decreasing low-density lipoprotein compared with high-density lipoprotein cholesterol levels. Overall these results are consistent with the concept that ATP citrate-lyase is an important enzyme in controlling substrate supply for lipid synthesis de novo and a potential enzyme target for hypolipidaemic intervention.

ATP Citrate (pro-S)-Lyase↗
PubMed1980

Citrate transport in Salmonella typhimurium: studies with 2-fluoro-L-erythro-citrate as a substrate.

The citrate analogue, 2-fluoro-L-erythro-[3,4,5,6-(14)C]citrate was synthesized as a probe for the citrate transport system of Salmonella typhimurium. This analogue was actively transported by an inducible energy-dependent transport system with high affinity for fluorocitrate (Km = 3.3 microM), and this transport system was inhibited competitively by citrate and isocitrate. Fluorocitrate was shown to be a competitive inhibitor of the citrate-binding protein (C protein) of this organism (Ki = 4-5 microM). Analogue resistant mutants were simultaneously defective in fluorocitrate transport as well as the C protein and the affected allele, tctC, was located at 59 units on the S. typhimurium chromosome map. These tctC mutants were shown to be specifically defective in K+-dependent fluorocitrate transport but still retained another system capable of transporting fluorocitrate in the presence of both Na+ and K+.

Binding, Competitive↗
PubMed1965

CITRATE AND THE CONVERSION OF CARBOHYDRATE INTO FAT. THE ACTIVITIES OF CITRATE-CLEAVAGE ENZYME AND ACETATE THIOKINASE IN LIVERS OF STARVED AND RE-FED RATS.

1. The activity of citrate-cleavage enzyme varies in accordance with the nutritional state of the animal. It is suppressed on starvation and restored on re-feeding after starvation. 2. The increase in enzyme activity that occurs on re-feeding starved animals depends on the diet. It is largest on diets high in carbohydrate and low in fat, and smallest on diets high in fat. Intermediate increases are obtained with balanced diets. 3. The ratio of activities of citrate-cleavage enzyme to acetate thiokinase varies from 2.5 for animals maintained on a balanced diet to 20 for animals re-fed with a diet high in carbohydrate. 4. The changes in activity of citrate-cleavage enzyme correlate with changes in the rate of fatty acid synthesis and provide evidence for the involvement of the citrate-cleavage reaction in fatty acid synthesis.

ATP Citrate (pro-S)-Lyase↗
PubMed2002

A new dinuclear vanadium(V)-citrate complex from aqueous solutions. Synthetic, structural, spectroscopic, and pH-dependent studies in relevance to aqueous vanadium(V)-citrate speciation.

Vanadium interactions with low molecular mass binders in biological fluids entail the existence of vanadium species with variable chemical and biological properties. In the course of efforts to elucidate the chemistry related to such interactions, we have explored the oxidative chemistry of vanadium(III) with the physiologically relevant tricarboxylic citric acid. Aqueous reactions involving VCl(3) and anhydrous citric acid, at pH approximately 7, resulted in blue solutions. Investigation into the nature of the species arising in those solutions revealed, through UV/visible and EPR spectroscopies, oxidation of vanadium(III) to vanadium(IV). Further addition of H(2)O(2) resulted in the oxidation of vanadium(IV) to vanadium(V), and the isolation of a new vanadium(V)-citrate complex in the form of its potassium salt. Analogous reactions with K(4)[V(2)O(2)(C(6)H(4)O(7))(2)].6H(2)O and H(2)O(2) or V(2)O(5) and citrate at pH approximately 5.5 afforded the same material. Elemental analysis pointed to the molecular formulation K(4)[V(2)O(4)(C(6)H(5)O(7))(2)].5.6H(2)O (1). Complex 1 was further characterized by FT-IR and X-ray crystallography. 1 crystallizes in the triclinic space group P(-)1, with a = 11.093(4) A, b = 9.186(3) A, c = 15.503(5) A, alpha = 78.60(1) degrees, beta = 86.16(1) degrees, gamma = 69.87(1) degrees, V = 1454.0(8) A(3), and Z = 2. The X-ray structure of 1 reveals the presence of a dinuclear vanadium(V)-citrate complex containing a V(V)(2)O(2) core. The citrate ligands are triply deprotonated, and as such they bind to vanadium(V) ions, thus generating a distorted trigonal bipyramidal geometry. Binding occurs through the central alkoxide and carboxylate groups, with the remaining two terminal carboxylates being uncoordinated. One of those carboxylates is protonated and contributes to hydrogen bond formation with the deprotonated terminal carboxylate of an adjacent molecule. Therefore, an extended network of hydrogen-bonded V(V)(2)O(2)-core-containing dimers is created in the lattice of 1. pH-dependent transformations of 1 in aqueous media suggest its involvement in a web of vanadium(V)-citrate dinuclear species, consistent with past solution speciation studies investigating biologically relevant forms of vanadium.

Journal Article↗
PubMed2002

Growth of Bacillus subtilis on citrate and isocitrate is supported by the Mg2+-citrate transporter CitM.

Bacillus subtilis 168 was assayed for its growth on tricarboxylic acid (TCA) cycle intermediates and related compounds as the sole carbon sources. Growth of the organism was supported by citrate, D-isocitrate, succinate, fumarate and L-malate, whereas no growth was observed in the presence of cis-aconitate,2-oxoglutarate, D-malate, oxaloacetate and tricarballylate. Growth of the organism on the tricarboxylates citrate and D-isocitrate required the presence of functional CitM, an Mg(2+)-citrate transporter, whereas its growth on succinate, fumarate and L-malate appeared to be CitM-independent. Interestingly, the naturally occurring enantiomer D-isocitrate was favoured over L-isocitrate by the organism. Like citrate, D-isocitrate was shown to be an inducer of citM expression in B. subtilis. The addition of 1 mM Mg(2+) to the growth medium improved growth of the organism on both citrate and D-isocitrate, suggesting that D-isocitrate was taken up by CitM in complex with divalent metal ions. Subsequently, the ability of CitM to transport D-isocitrate was demonstrated by competition experiments and by heterologous exchange in right-side-out membrane vesicles prepared from E. coli cells expressing citM. None of the other TCA cycle intermediates and related compounds tested were recognized by CitM. Uptake experiments using radioactive (63)Ni(2+) provided direct evidence that D-isocitrate is transported in complex with divalent metal ions.

Bacillus subtilis↗