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PubMed2000

Regional citrate anticoagulation in continuous venovenous hemodiafiltration.

Over the past several years, continuous venovenous hemodiafiltration (CVVHDF) using pump-driven devices has gained wide acceptance as a form of renal replacement therapy for critically ill patients with acute renal failure. More recently, regional citrate anticoagulation has proven useful as a method of anticoagulating CVVHDF circuits, particularly in those patients at high risk for bleeding. However, an easy and convenient method for guiding the dose of citrate infusion has not previously been described. We describe the use of an algorithm using posthemofilter levels of ionized calcium to guide the dose of administered regional citrate on the survival time and urea and creatinine clearances of 24 Hospal AN69HF hemofilters. Nine patients with acute and chronic renal failure requiring CVVHDF were studied. The median filter survival time when using the postfilter ionized calcium algorithm was 3.4 days, with a survival probability of 46% (95% confidence interval [CI], 17 to 71). Random-effects linear regression analysis did not show a significant decline in blood-side urea clearance (P = 0.041) or creatinine clearance (P = 0. 308). Moreover, definite bleeding complications occurred with an incidence rate of 0.045/person-day on citrate anticoagulation (95% CI, 0.006 to 0.16), and occult bleeding occurred with an incidence rate of 0.091/person-day on citrate anticoagulation (95% CI, 0.03 to 0.23). Guiding regional citrate anticoagulation through the use of posthemofilter ionized calcium levels is a safe and effective method of prolonging filter life during CVVHDF.

Acidosis↗
PubMed1980

Isotachophoretic determination of urinary citrate in native urine.

The technique of isotachophoresis has been used to develop a specific and sensitive method for the determination of citrate in unprocessed urine. The specificity of the isotachophoretic method was assessed using citrate lyase which caused disappearance of the isotachophoretic citrate signal. The isotachophoretic method compared favourably with the enzymatic method (citrate lyase) for urinary citrate. The normal range for urinary citrate in 25 healthy individuals, as found by isotachophoresis, was 0.33-2.89 mmol/24 h with a mean of 2.1 mmol/24 h.

Citrates↗
PubMed1995

Effect of oxaloacetate and phosphorylation on ATP-citrate lyase activity.

ATP-citrate lyase (CL) catalyzes the conversion of citrate and CoA to oxaloacetate (OA) and acetyl-CoA. As the coupled malic dehydrogenase (MDH) assay is not able either to study the effect of oxaloacetate (OA) on CL activity or to measure accurately CL activity in biological samples, a new assay was developed. The CL-citrate coupled CAT assay measures the amount of acetyl-CoA formed by transferring radiolabeled acetyl-CoA synthesized from [14C]citrate to chloramphenicol with chloramphenicol acetyltransferase (CAT). Employing this assay, the rate of increase in acetyl-CoA synthesis from citrate is linear with respect to added CL. Kinetic values for ATP, CoA and citrate are similar to those obtained using the MDH assay. The effect of CL phosphorylation on enzyme activity was determined. CL phosphorylated by cAMP-dependent protein kinase or by this kinase and glycogen synthase kinase-3 (GSK-3) decreases the apparent Vmax without changing the apparent Km. The effect of OA, a product of the enzyme reaction, on CL activity was also determined. Computational analysis of the data obtained without added OA and at three concentrations of OA indicate that the apparent Km for the substrate is not altered even though the apparent Vmax is decreased. The effect of OA on the activity of phosphorylated enzyme was also determined. OA decreases the apparent Vmax of the phosphorylated enzyme to the same extent as in control CL. This assay is able to measure CL activity in cytosol from 3T3-L1 adipocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

3T3 Cells↗
PubMed1989

Citrate synthase stabilizes the enethiolate of acetyldithio coenzyme A.

Citrate synthase catalyzes the slow condensation of acetyldithio-CoA [Ac(= S)CoA] with oxalacetate to form thiocitrate [Wlassics, I.D., Stille, C., & Anderson, V.E. (1988) Biochim. Biophys. Acta 952, 269]. During the transient approach to steady state an observable amount of the dithioester absorbance disappears. The amplitude of the decrease in absorbance corresponds to 0.32, 0.03, and 0.02 enzyme equiv at pH 8.3, 7.5, and 6.6, respectively. The difference spectra from before and after the transient exhibit the dithioester lambda max at 306 nm. Acid quenching of a stiochiometric reaction between Ac(= S)CoA and citrate synthase following the transient quantitatively regenerates Ac(= S)CoA, indicating carbon-carbon bond formation had not yet occurred. The apparent first-order rate constant of the transient is independent of Ac(= S)CoA concentration and increases with decreasing pH, being 0.007, 0.016, and 0.04 s-1 at pH 8.3, 7.5, and 6.6, respectively. 2-Fluoroacetyldithio-CoA is a better inhibitor of citrate synthase, Ki = 300 nM, and substrate, Vmax = 2 X 10(-3) s-1, than Ac(= S)CoA. 1H NMR experiments indicate that citrate synthase catalyzes the exchange of the alpha-hydrogens of Ac(= S)CoA with turnover numbers of 0.13 and 0.54 s-1 at pD 7.9 and 7.2, respectively. Analysis of the proton and deuterium decoupled 13C NMR spectra of [2-13C]Ac(= S)CoA that has exchanged 37% of the alpha-hydrogens in the presence of citrate synthase indicates that the relative proportions of CH3, CH2D, CHD2, and CD3 were 0.29, 0.39, 0.25, and 0.07, respectively. This statistical distribution indicates each exchange event is independent. The data indicate that citrate synthase stabilizes the ionized form of Ac(= S)CoA by 5 kcal/mol relative to the un-ionized form, that the ionized dithioester is on the reaction pathway, and that below pH 8.3 the slow carbon-carbon bond forming reaction is responsible for the 10(6) decrease in Vmax caused by substituting sulfur for oxygen in the thioester carbonyl.

Acyl Coenzyme A↗
PubMed1976

The binding of reduced nicotinamide adenine dinucleotide to citrate synthase of Escherichia coli K12.

Citrate synthase from Escherichia coli enhances the fluorescence of its allosteric inhibitor, NADH, and shifts the peak of emission of the coenzyme from 457 to 428 nm. These effects have been used to measure the binding of NADH to this enzyme under various conditions. The dissociation constant for the NADH-citrate synthase complex is about 0.28 muM at pH 6.2, but increases toward alkaline pH as if binding depends on protonation of a group with a pKa of about 7.05. Over the pH range 6.2-8.7, the number of binding sites decreases from about 0.65 to about 0.25 per citrate synthase subunit. The midpoint of this transition is at about pH 7.7, and it may be one reflection of the partial depolymerization of the enzyme which is known to occur in this pH range. A gel filtration method has been used to verify that the fluorescence enhancement technique accurately reveals all of the NADH molecules bound to the enzyme in the concentration range of interest. NAD+ and NADP+ were weak competitive inhibitors of NADH binding at pH 7.8 (Ki values greater than 1 mM), but stronger inhibition was shown by 5'-AMP and 3'-AMP, with Ki values of 83 +/- 5 and 65 +/- 4 muM, respectively. Acetyl-CoA, one of the substrates, and KCl, an activator, also inhibit the binding in a weakly cooperative manner. All of these effects are consistent with kinetic observations on this system. We interpret our results in terms of two types of binding site for nucleotides on citrate synthase: an active site which binds acetyl-CoA, the substrate, or its analogue 3'-AMP; and an allosteric site which binds NADH or its analogue 5'-AMP and has a lesser affinity for other nicotinamide adenine dinucloetides. When the active site is occupied, we propose that NADH cannot bind to the allosteric site, but 5'-AMP can; conversely, when NADH is the in the allosteric site, the active site cannot be occupied. In addition to these two classes of sites, there must be points for interaction with KCl and other salts. Oxaloacetate, the second substrate, and alpha-ketoglutarate, an inhibitor whose mode of action is believed to be allosteric, have no effect on NADH binding to citrate synthase at pH 7.8. When NADH is bound to citrate synthase, it quenches the intrinsic tryptophan fluorescence of the enzyme. The amount of quenching is proportional to the amount of NADH bound, at least up to a binding ratio of 0.50 NADH per enzyme subunit. This amount of binding leads to the quenching of 53 +/- 5% of the enzyme fluorescence, which means that one NADH molecule can quench all the intrinsic fluorescence of the subunit to which it binds.

Binding Sites↗
PubMedDate not supplied

Suppressed acid formation by cofeeding of glucose and citrate in Bacillus cultures: emergence of pyruvate kinase as a potential metabolic engineering site.

Microbial cultures typically produce acids when metabolizing the common carbon source, glucose. Acid production not only represents a waste of carbon, but its accumulation can limit cell concentration and culture stability, thereby reducing productivity. On the basis of prior work, acid production was attributed to be due to a mismatch between glycolytic and tricarboxylic acid (TCA) cycle capacities. To suppress acid production, a strategy entailing adding citrate to glucose minimal medium proved extremely effective. The effect of citrate on in-vivo flux distribution was quantified using a detailed flux-model. When the molar glucose-citrate ratio was varied between 3 and 6, a significant reduction in glycolytic flux and essentially complete suppression of acid formation was found as compared to chemostat cultures grown solely on glucose. Adding other biosynthetic precursors such as glutamine did not invoke the same suppression, thus indicating that citrate's effect is at the regulatory level. We hypothesized that the reduction of glycolytic flux in the presence of citrate results from its transport being coupled with the uptake of divalent metal ions. Citrate transport alters the intracellular balance of metal ions which in turn could trigger a sophisticated series of metabolic events leading to reduction of the activities of the pyruvate kinase and phosphofructokinase (PFK), the regulatory enzymes of glycolysis. On the basis of this scenario and other regulatory information, pyruvate kinase has emerged as a potential metabolic engineering site. It's deactivation in Bacillus subtilis or Escherichia coli strains is expected to yield constructs with a much lower tendency for making acid byproducts.

Bacillus↗
PubMed1981

Mechanism of volume expansion on citrate, ammonia, and acid excretion in the rat.

Potassium-depleted rats receiving sodium chloride or i.v. mannitol decrease their blood bicarbonate concentration isohydrically, reduce urinary citrate, and increase urinary ammonia excretion per milligram of urinary creatinine. To determine the mechanisms of these renal changes, we volume expanded normal rats with mannitol, normal saline, or saline bicarbonate solutions. Blood pH in each group remained constant, but blood bicarbonate fell significantly in the mannitol and saline-infused rats. In these two groups, urinary citrate per unit GFR decreased 27% and 25% (P less than 0.01) but urinary ammonia excretion per unit GFR increased 120% and 90% (P less than 0.01). By contrast, in saline bicarbonate rats, citrate excretion increased 27% and urinary ammonia excretion rose 29% (P greater than 0.2). Rats with metabolic acidosis given saline did not alter blood pH or bicarbonate. Citrate excretion per unit GFR increased 150% (P less than 0.02) but urinary ammonia excretion rose insignificantly by 11%. Calculated net tubular reabsorption of citrate increased in the mannitol and saline-infused rats. The rise in urinary pH in these two groups during expansion suggest that renal ammonia production was also increased. We conclude that volume expansion changes renal citrate and ammonia metabolism by isohydrically reducing blood bicarbonate concentration, thereby demonstrating another effect of bicarbonate, independent of pH, on renal metabolism.

Acid-Base Equilibrium↗
PubMed1993

Creatinine, calcium, citrate and acid-base in spinal cord injured patients.

The aim of this work was to recognise factors responsible for reduced citrate excretion, previously reported in patients with spinal cord lesions and possibly related to the occurrence of urinary tract stone or catheter blockage. Inter alia, a reference range for creatinine in plasma (34-88 mumol/l) was also obtained. Two groups of subjects were studied. The first group consisted of 64 male inpatients with spinal cord lesions and 20 male control subjects. The second group were 342 spinal patients who attended an outpatient clinic and 31 control subjects. Plasma calcium was within the normal range but higher in patients within 1 year of onset of the cord lesion than it was later or than was found in control subjects. Plasma pH and bicarbonate were within the normal range but higher in the patients than in the control subjects. When patients with urea-splitting infection were omitted the patients had a higher urinary pH and a lower urinary ammonium than the controls. Urinary and plasma citrate were lower in the patients than in the controls. Urinary citrate was related to urinary potassium and creatinine clearance. Fractional renal tubular reabsorption of citrate did not differ between patients with normal renal function and control subjects. Patients with normal glomerular filtration had lower filtered load of citrate than the controls. The coincidence of relative alkalosis and reduced citrate excretion may be relevant to the understanding of catheter blockage and urinary stone formation in spinal cord injured patients.

Acid-Base Equilibrium↗
PubMed1968

The effects of starvation and alloxan-diabetes on the contents of citrate and other metabolic intermediates in rat liver.

1. The content of citrate in ;freeze-clamped' livers from starved and alloxan-diabetic rats was measured by using the specific citrate assay method of Gruber & Moellering (1966). 2. The content of citrate fell progressively during a period of 48hr. starvation to reach a plateau value that is 50% of the value for livers from fed rats. Some possible explanations for the conflicting reports of changes in hepatic citrate content during starvation are discussed. 3. The hepatic contents of ATP, pyruvate, lactate, glycogen and the hexose phosphates were decreased during starvation, whereas those of acetyl-CoA and AMP were increased. 4. Acute alloxan-diabetes produced similar changes in the contents of these metabolic intermediates. 5. The effects of starvation and diabetes on the citrate and acetyl-CoA contents are discussed in relation to control of gluconeogenesis, fatty acid synthesis and the activity of citrate synthase.

Adenine Nucleotides↗
PubMed1970

The sensitivity of acetyl-coenzyme A carboxylase to citrate stimulation in a homogenate of rat liver containing subcellular particles.

1. Although citrate is known to activate purified preparations of acetyl-CoA carboxylase, it had no stimulatory effect on the incorporation of [(14)C]acetate into long-chain fatty acids in a whole homogenate of rat liver (S(0.7)) under conditions in which the activity of acetyl-CoA carboxylase was rate-limiting for fatty acid synthesis. 2. The rate of incorporation of acetyl carbon into fatty acids was estimated in S(0.7) preparations incubated with [(14)C]acetate, by measuring the specific radioactivity of the acetyl carbon of acetyl-CoA and the incorporation of (14)C into fatty acids. These estimates were compared with estimates of acetyl-CoA carboxylase activity in the S(0.7) preparation obtained by direct assay in conditions in which the enzyme was in the fully activated state. 3. In the absence of citrate, incorporation of acetyl carbon into fatty acids was about 75% of the value expected if the acetyl-CoA carboxylase in the S(0.7) preparation were in the fully activated state. 4. Incorporation of acetyl carbon into fatty acids in the S(0.7) preparation was stimulated by citrate, but the effect was many times less than the stimulation of [(14)C]acetate incorporation by citrate in particle-free preparations. 5. When the mitochondria and microsomes were removed from the S(0.7) preparation, [(14)C]acetate incorporation into fatty acids fell to a negligible value and the preparation became highly sensitive to stimulation by citrate. 6. It is suggested that in the presence of mitochondria and microsomes, and in the intact liver cell, the degree of activation of acetyl-CoA carboxylase is such that citrate activation may not be of physiological significance.

Acetates↗
PubMed1983

Myocardial exchanges of glutamate, alanine and citrate in controls and patients with coronary artery disease.

1. Myocardial exchanges of plasma alanine, glutamate, citrate, lactate, glucose and free fatty acids were determined in 17 patients with coronary artery disease and in seven control subjects during rest, atrial pacing and recovery. 2. Myocardial release of alanine was demonstrated in all subjects. The amount released was higher in patients with coronary artery disease than in controls. In the patients alanine release was related to severity of coronary artery stenosis. 3. All subjects showed myocardial uptake of glutamate, higher in patients than in controls at rest and during recovery. During atrial pacing myocardial glutamate extraction remained unchanged in controls but decreased in patients. 4. Citrate was released by the heart in all controls and patients. During recovery citrate output was higher in patients than in controls. 5. Myocardial alanine and citrate release during recovery were positively correlated. Both were positively related to myocardial uptake of glutamate during recovery and to the decrease in glutamate extraction during pacing. 6. The results indicate changed myocardial citrate and amino acid metabolism in coronary artery disease. Measurement of myocardial exchanges of glutamate, alanine and citrate in addition to lactate is suggested as a sensitive biochemical test in assessing myocardial ischaemia in man.

Aged↗
PubMed1996

Long-term effects of potassium citrate therapy on the formation of new stones in groups of recurrent stone formers with hypocitraturia.

OBJECTIVE: To compare stone formation rates before (as total rates and during remote periods) and after therapy with potassium citrate in patients with hypocitraturia. PATIENTS AND METHODS: The study comprised 15 patients with hypocitraturia only (Group I) and 12 patients with hypocitraturia associated with other abnormalities (Group II), all of whom were recurrent stone formers. Their urine chemistry, including citrate, was measured before and after treatment. RESULTS: In both groups, the urinary citrate concentration increased significantly to within normal limits during therapy with potassium citrate (P < 0.005). The rate of total stone formation in patients in Group I decreased significantly from 0.7/year before to 0.13/year after treatment (P < 0.005). The corresponding remote stone formation rate before (0.88/year) was significantly greater than the rate after treatment (0.13/year; P < 0.005; follow-up 4.6 +/- 1.9 years). Patients in Group II showed a similar striking decrease in total stone formation rate, from 1.2/year to 0.08/year after treatment (P < 0.005). The corresponding remote stone formation rate (1.66/year) before was significantly greater than that after treatment (0.08/year; P < 0.005; follow-up 4.1 +/- 1.6 years). There was a remission rate of 93% for stone formation over the complete follow-up. CONCLUSION: Potassium citrate appears to be the drug of choice in the long-term treatment of patients with hypocitraturia as it not only decreases the rate of stone formation but also maintains normal citrate levels in the urine.

Administration, Oral↗
PubMedDate not supplied

Relationship of physical symptoms, ECG, free calcium, and other blood chemistries in reinfusion with citrated blood.

Changes in ECG, free calcium (CaF), and other biochemical parameters were measured during reinfusion of citrate anticoagulated blood in 12 subjects undergoing plateletpheresis. Physical symptoms during the procedure were also monitored. The CaF was found to correlate best with the Q-oTc interval as compared to the Q-oT, Q-Tc, or Q-T interval. While the correlation was significant (r = 0.592, p less than .001), the Q-oTc could not predict the CaF. A number of other blood constituents were found to change during plateletpheresis, with most directly related to either citrate administration or hemodilution. Severe physical symptoms were found in one subject and no symptoms in three. In the subjects without symptoms the changes in Q-oTc, Pi, alkaline phosphatase, and glucose through the plateletpheresis procedure were different from changes in all subjects. The decrease in glucose level was the most striking single factor correlating with the lack of physical symptoms during the citrate-induced hypocalcemia associated with plateletpheresis. It is concluded that monitoring of the ECG cannot substitute for direct measurement of free calcium in citrate-induced hypocalcemia, that the physical symptoms associated with similar levels of hypocalcemia are variable, that glucose level may be a marker for the effects of citrate-induced hypocalcemia, and that lowered citrate loads during plateletpheresis appear warranted.

Adult↗
PubMedDate not supplied

Effect of citrate anticoagulants on factor VIII levels in plasma.

The citrate anticoagulants used during blood collection have been developed for their benefits to red cells. The concentrations in which they are used are strictly regulated in the United States: citrate-phosphate-dextrose-adenine (CPDA) is used in a 1:8 ratio for the collection of whole blood, whereas 4 percent sodium citrate (NaCit) is used in a 1:10 ratio for manual plasmapheresis. Acid-citrate-dextrose formula A (ACD-A) or formula B (ACD-B) and NaCit are commonly used in a 1:12 or 1:15 ratio during automated plasmapheresis. These anticoagulants have different initial and final pH values and citrate concentrations and different effects on the recovery of factor VIII (FVIII) in the plasma. NaCit has a higher initial pH (6.64) than ACD-A (4.98), ACD-B (5.60), or CPDA (5.12). The effects of these different anticoagulants on plasma constituents obtained from six healthy subjects were studied. In standard citrate concentrations, the FVIII level was significantly lower (p less than 0.05) in the NaCit used for manual plasmapheresis than in either of the ACD solutions used in automated plasmapheresis (104 U/dl vs. 153 and 160 U/dl). When various ratios of NaCit to blood were used, the pH increased from 7.62 at a 1:10 dilution to 7.65 at a 1:50 dilution. As expected, a progressive decrease in anticoagulant level was associated with an increase in ionized calcium and also in the level of FVIII, with the latter values rising from 104 U per dl at 1:10 to 137 at 1:20 and 148 U per dl at 1:30. Clot formation was detected only at a ratio of 1:35.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenine↗
PubMed1996

Concentration of citrate anticoagulant in peripheral blood progenitor cell collections.

BACKGROUND: Peripheral blood progenitor cell (PBPC) collection by hemapheresis has become widely used in recent years. For anticoagulation during cytapheresis, citrate solutions, commonly ACD-A, are used, at a recommended anticoagulant-to-whole blood ratio of 1:11 to 1:12. Although the apheresis procedure is generally well tolerated, the most common patient complaints are attributable to transient hypocalcemia, which is a side effect of the citrate anticoagulant. Patients experiencing discomfort due to hypocalcemia are sometimes managed by a decrease in the flow rate of the anticoagulant. CASE REPORTS: Two cases are reported in which seemingly minor reductions in the anticoagulant: whole blood ratio appeared to cause gelation of freezing solution prepared from plasma that was collected in addition to PBPCs for use in the cryopreservation of cells. In both cases, the final ratio of citrate anticoagulant to whole blood was less than 1:12. Gelation occurred when plasma collected under these conditions was used to prepare freezing solution. CONCLUSION: The addition of heparin to this plasma, or the addition of ACD-A to correct the anticoagulant:whole blood ratio, prevented the gelation of freezing solution, which suggests that coagulation activation in the autologous plasma specimen was implicated in the subsequent gelation. During cytapheresis for PBPC collection, citrate-containing anticoagulants should be used at the recommended ratio of 1:12, or with more anticoagulant than usual. Tolerance for a reduced concentration of citrate may be more limited than is generally appreciated. When plasma is collected in addition to PBPCs, heparin should be added to both the cells and the plasma as soon as possible after the collection. Patients undergoing PBPC and stem cell collection should be given supplemental calcium, rather than less anticoagulant, to alleviate the discomfort associated with citrate.

Adult↗
PubMed1983

Mössbauer and EPR studies of activated aconitase: development of a localized valence state at a subsite of the [4Fe-4S] cluster on binding of citrate.

During activation of aconitase a ferrous ion is incorporated into a [3Fe-4S] cluster to yield a structure with a [4Fe-4S] core. Using 57Fe or 56Fe for activation we have studied with Mössbauer spectroscopy the beef heart enzyme in the presence of citrate. Our studies show that the environment of one iron site (Fea) of the [4Fe-4S] cluster is drastically altered in the presence of citrate. Fea is the iron acquired during activation of aconitase. In the oxidized [4Fe-4S]2+ state two species with enzyme-bound substrate are observed, whereas only one is observed in the reduced [4Fe-4S]+ state. The Mössbauer parameters of Fea reveal that the site has acquired substantial high-spin ferrous character. This is most pronounced in the 1+ state where at Fea the cluster exhibits a localized valence state. The dramatic increase of the isomer shift upon substrate binding strongly suggests that the ligand environment of Fea has become at least five-coordinate and that the cluster may function as a Lewis acid. In the absence of citrate the EPR spectra of the active [4Fe-4S]+ enzyme (g1,2,3 = 2.06, 1.93, 1.86) show no hyperfine broadening in the presence of H2 17O. However, in the presence of citrate (g1,2,3 = 2.04, 1.85, 1.78) sizable transferred hyperfine interactions are observed; under the experimental conditions the hydroxyl groups of citrate and isocitrate as well as water are labeled with 17O. We did not detect broadening by 17O-labeled carboxyl groups of citrate in H2 16O. Implications for the mechanism of aconitase are discussed.

Aconitate Hydratase↗
PubMed1993

Cloning and characterization of the Salmonella typhimurium-specific chemoreceptor Tcp for taxis to citrate and from phenol.

Salmonella typhimurium shows an attractant response to citrate and a repellent response to phenol, and a chemoreceptor mediating these responses has been identified and named Tcp (taxis to citrate and away from phenol). Tcp is one of the methyl-accepting chemotaxis proteins that have a molecular mass of approximately 60 kDa estimated by SDS/PAGE, and its methylation level is increased by citrate and decreased by phenol. Tcp also mediates an attractant response to metal-citrate complexes. The complete nucleotide sequence of the tcp coding region has been determined. The deduced amino acid sequence of Tcp, consisting of 547-amino acid residues, is homologous with that of the aspartate chemoreceptor of S. typhimurium. Thus, Tcp is another member of the bacterial transmembrane chemoreceptor family. Because citrate is a good carbon source for S. typhimurium but is not a carbon source for the closely related species Escherichia coli and because citrate utilization is used as a key diagnostic character to distinguish these species, it is reasonable to assume that Tcp is specific to S. typhimurium.

Amino Acid Sequence↗
PubMed1995

Phosphorylation of ATP-citrate lyase by nucleoside diphosphate kinase.

Rat liver nucleoside diphosphate kinase (NDPK) and PC12 cell cytosol were used to determine whether NDPK could function as a protein kinase. NDPK was phosphorylated on its catalytic histidine using [gamma-32P]ATP, and the phosphorylated NDPK separated from [gamma-32P]ATP. The addition of phosphorylated NDPK to dialyzed PC12 cell cytosol resulted in the phosphorylation of a protein with a subunit molecular mass of about 120 kDa. This phosphorylation appeared to occur by a direct transfer of a phosphoryl group from the catalytic histidine of NDPK to a histidine on the 120-kDa protein. The 120-kDa protein was partially purified and shown by peptide sequencing to be ATP-citrate lyase. ATP-citrate lyase is the primary source of cytosolic acetyl-CoA. NDPK phosphorylated the histidine at the catalytic site of ATP-citrate lyase. This histidine can also be phosphorylated by ATP, and its phosphorylation is the first step in the conversion of citrate and CoA to oxaloacetate and acetyl-CoA by ATP-citrate lyase. The level of phosphorylation of PC12 cell ATP-citrate lyase by phosphorylated NDPK was comparable with that by ATP. Thus, in addition to its nucleoside diphosphate kinase activity, NDPK can function as a protein kinase.

ATP Citrate (pro-S)-Lyase↗