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At least 19 recordsLinked to original sources
PubMed2002

Final report on the safety assessment of acetyl triethyl citrate, acetyl tributyl citrate, acetyl trihexyl citrate, and acetyl trioctyl citrate.

Acetyl Triethyl Citrate, Acetyl Tributyl Citrate, Acetyl Trihexyl Citrate, and Acetyl Trioctyl Citrate all function as plasticizers in cosmetics. Additionally, the Trihexyl and Trioctyl forms are described as skin-conditioning agents-emollients, although there are currently no reported uses of Acetyl Trihexyl Citrate or Acetyl Trioctyl Citrate. Acetyl Triethyl Citrate and Acetyl Tributyl Citrate are used in nail products at concentrations up to 7%. Recognizing that there are no reported uses of Acetyl Trihexyl or Trioctyl Citrate, if they were to be used in the future, their concentration of use is expected to be no higher than that reported for Acetyl Triethyl and Tributyl Citrate. These ingredients were sufficiently similar in structure that safety test data on one were considered applicable to all. Approximately 99% of orally administered Acetyl Tributyl Citrate is excreted-intermediate metabolites include acetyl citrate, monobutyl citrate, acetyl monobutyl citrate, dibutyl citrate, and acetyl dibutyl citrate. In acute, short-term, subchronic, and chronic feeding studies, these ingredients were relatively nontoxic. Differences from controls were either not statistically significant or not related to any organ toxicity. Ocular exposures produced moderate reactions that cleared by 48 hours after instillation. Dermal application was not toxic in rabbits. In a guinea pig maximization test, Acetyl Triethyl Citrate was a sensitizer whereas Acetyl Tributyl Citrate was not. Limited clinical testing of Acetyl Triethyl Citrate and Acetyl Tributyl Citrate was negative for both skin irritation and sensitization. These clinical data were considered more relevant than the guinea pig maximization data, suggesting to the Cosmetic Ingredient Review Expert Panel that none of these ingredients would be a sensitizer. Physiologic effects noted with intravenous delivery of Acetyl Triethyl Citrate or Acetyl Tributyl Citrate include dose-related decreases in blood pressure and intestinal muscular spasms. These ingredients were not genotoxic in bacterial or mammalian test systems. No significant differences in tumor induction (lymphomas) were noted in rats fed Acetyl Tributyl Citrate for 2 year. Acetyl Tributyl Citrate was not a developmental or reproductive toxicant in studies in mice and rats. Based on all the available data, these ingredients were considered safe as used in cosmetics.

Animals↗
PubMed1999

Magnesium, citrate, magnesium citrate and magnesium-alkali citrate as modulators of calcium oxalate crystallization in urine: observations in patients with recurrent idiopathic calcium urolithiasis.

The effects of magnesium (Mg) and citrate on the metastable limit of calcium oxalate (CaOx) solubility (synonym: tolerable oxalate TO) were examined in artificial urine and in postprandial urine of male patients with idiopathic calcium urolithiasis (ICU). In artificial urine increasing pH, Mg and citrate elevate TO, decrease CaOx supersaturation only marginally, but elevate considerably free citrate; the effect of Mg alone was small in comparison with citrate alone, and the effects of both substances appeared additive. In ICU patients, matched for sex, age and CaOx supersaturation to non-stone-forming controls, TO was decreased (mean values 0.33 vs. 0.52 mM/l in controls, P < 0.05). Additional significant (P < 0.05) differences were found between ICU and controls: the former exhibited increased CaOx crystal growth, decreased crystal agglomeration time, a more acidic urinary pH, increased concentrations of free calcium and free Mg, and decreased free oxalate and free citrate. After ingestion of a urine-acidifying test meal, or this meal supplemented with either neutral Mg citrate or Mg-alkali citrate, by three groups of male ICU patients, matched for age and CaOx supersaturation, only the last-named preparation evoked an increase in TO and a decrease in crystal diameter, while the normally occurring pH decline from fasting urine was virtually abolished, and the ratios urinary Mg/citrate and calcium/citrate tended towards low values. In contrast, Mg citrate increased crystal agglomeration time, while changes in the other parameters were only insignificant. The crystals formed in urine were CaOx di- and monohydrate (by electron microscopy), and energy dispersive X-ray analysis showed calcium peaks exclusively. However, chemical analysis of crystals verified the presence not only of oxalate and calcium, but also of Mg, phosphate, citrate, and urate; moreover, these crystal constituents seemed to be influenced by Mg citrate and Mg-alkali citrate in different ways. It was concluded that (1) Mg and citrate are effectors of TO in artificial and natural urine; (2) in ICU, low TO and other disturbed CaOx crystallization parameters appear related to the prevailing low urinary pH and low free citrate; (3) Mg-alkali citrate inhibits CaOx crystallization, probably via actions of the citrate, but not the Mg. Because of the eminent role of Mg in human health and ICU, further studies on crystallization after oral intake of Mg in the form of citrate are warranted.

Calcium Oxalate↗
PubMed1991

[Citrate as an inhibitor of stone formation--with reference to intestinal citrate absorption and the influence of citrate on intestinal calcium absorption].

The response of serum citrate to the oral citrate load was studied in seven healthy subjects. Serum citrate was significantly elevated from 15 to 60 min post-load with some individual variations. In 27 stone-formers serum citrate and the response to the oral citrate administration was studied and compared with the results obtained on healthy subjects. The serum citrate concentration of stone-formers was 1.99 +/- 0.49 mg/dl as compared to 1.61 +/- 0.35 mg/dl in healthy subjects. After citrate administration serum citrate increased significantly in both groups, but no significant difference was shown in response to the oral citrate load between these two groups (3.44 +/- 0.94 mg/dl in stone-formers, 3.16 +/- 0.38 mg/dl in healthy subjects). In Sprague-Dawley rats each weighing about 200 g urinary citrate and calcium excretion were studied after administration of sodium citrate or calcium chloride or both. The concomitant equimolar administration of sodium citrate and calcium chloride did not have significant influence on urinary citrate or calcium excretion as compared when citrate or calcium was given alone. However, the calcium excretion was significantly decreased with the administration of citrate and calcium ata molar ratio of 1:2.

Animals↗
PubMed1989

Comparative studies of radiotracer citrates in oncological models--2. 153Sm-citrate and 67Ga-citrate.

153Sm-citrate solutions were prepared from enriched 152Sm2O3 which had been irradiated at 10(12)n cm-2 s-1 in the University of Alberta Slowpoke reactor. 153Sm was rapidly bound (93% in 2 h) by Melanoma 2AB cells in tissue culture upon incubation in the presence of 153Sm-citrate (1.9 nmol 10(6) cells). In vitro ultracentrifugation studies of 153Sm-citrate solutions showed that colloid formation under incubation conditions could have been responsible in part for the uptake by cultured cells. Low uptakes (less than 1% in 2h) of 67Ga-citrate were seen under similar conditions. 153Sm-citrate injected into BDF1 mice (Lewis lung carcinoma) and Copenhagen x Fisher rats (Dunning R3327-H prostatic tumors) was concentrated mainly in the liver, with some tumor and bone uptake. The percent of injected dose per organ for 153Sm and 67Ga in the murine and rat models respectively, 24 h after i.v. dosing, was 17.2 +/- 4.7 and 2.0 +/- 0.6 (tumor), 63.9 +/- 7.9 and 14.4 +/- 1.4 (liver) and 0.6 +/- 0.1 and 1.3 +/- 0.1 (blood); % injected dose g-1 femur was 6.2 +/- 2.7 and 12.9 +/- 2.7, respectively. Scintigrams of rats showed qualitative biodistributions similar to the quantitative mouse data obtained by dissection studies. The high hepatic uptake detracted from the otherwise superior tumor localization of 153Sm-citrate when compared to 67Ga-citrate in these models. The murine Lewis lung tumor index (% injected dose g-1 tumor x tumor: blood) was 303.6 for 153Sm-citrate and 48.9 for 67Ga-citrate, 24 h after injection.

Animals↗
PubMed1986

The effect of testosterone on citrate synthesis and citrate oxidation and a proposed mechanism for regulation of net citrate production in prostate.

Citrate oxidation by rat ventral prostate was reduced by castration and increased by testosterone administration. Similarly, the mitochondrial aconitase activity was decreased by castration; whereas cytosol aconitase was unaffected. The rate of citrate oxidation is extremely low in prostate. Castration also decreased mitochondrial aspartate aminotransferase activity while having no effect on the cytosol isoenzyme. Testosterone markedly stimulated the net production of citrate from aspartate plus glutamate by prostate mitochondria. These studies support the proposal that aspartate is a major source of oxalacetate for citrate production, and that a "glutamate-aspartate-citrate" pathway may be functional in prostate mitochondria. In addition, testosterone can regulate citrate production by a specific effect on mitochondrial aspartate aminotransferase activity. Testosterone also regulates the flux of citrate through the Krebs cycle, but this represents only a small proportion of the citrate accumulated. These conditions would be consistent with the function of prostate epithelium in accumulating and secreting citrate.

Acetyl Coenzyme A↗
PubMed1998

Reappraisal of the quantity and nature of renal calcifications and mineral metabolism in the magnesium-deficient rat. Effects of treatment with potassium citrate or the combination magnesium citrate and potassium citrate.

There is an urgent need for drugs capable of inhibiting renal calcifications, nephrocalcinosis and stones included, in humans. Current anticalcification medication is based mainly on alkalinization of the metabolism using potassium-containing citrate alone, despite the fact that calcium stone patients suffer marginally from both magnesium and potassium deficiency. We investigated the anticalcification efficacy of oral potassium citrate versus the combined administration of this drug and magnesium citrate in the magnesium-deficient rat developing corticomedullary nephrocalcinosis and luminal microliths in the long term. Among other things we employed specific stains for calcium and oxalate, light microscopy and element analysis for renal tissue and calcifications, respectively. In addition, minerals in renal tissue, urine and plasma were determined, as well as the state of extracellular calcium homeostasis. Magnesium deficiency caused pure calcium phosphate tissue deposits, containing no magnesium, but no deposition of calcium oxalate in the tubular lumen; tissue magnesium, calcium and phosphorus were increased, and there was marked potassium wastage via urine; despite mild hypercalcemia other signs of hyperparathyroidism were not found. Alkalinization with the two kinds of medication evoked an increase in urinary pH, citrate, and potassium; however, potassium citrate alone tended to aggravate renal concretions, whereas the combination of this drug with magnesium citrate completely prevented concretions. It was concluded that: (1) magnesium deficiency-induced calcifications are oxalate-free and are not sensitive to mobilization by alkalinization with potassium citrate, which might explain the failure of the drug to prevent stone recurrence in clinical stone patients, and (2) the combination of potassium citrate and magnesium citrate, which shows enormous anticalcification efficacy, deserves high priority in clinical trials aimed at evaluating strategies for the prevention of stones.

Animals↗
PubMed1977

Reactivity and inhibitor potential of hydroxycitrate isomers with citrate synthase, citrate lyase, and ATP citrate lyase.

The four isomers of hydroxycitrate have been tested as substrates and inhibitors for citrate synthase, citrate lyase, and ATP citrate lyase. None of the isomers served as a substrate for citrate synthase and they were moderate to weak inhibitors of this reaction. Of the four isomers, only (pncit)-(2S)-2-hydroxycitrate did not serve as a substrate for citrate lyase while (pncit)-(4S)-4-hydroxycitrate was the only isomer which did not serve as a substrate for ATP citrate lyase. No consistent pattern of reactivity or inhibitor potency was seen with the different isomeric hydroxycitrates. It is proposed that more than one mode of binding is possible between the isomers and the three different active sites.

ATP Citrate (pro-S)-Lyase↗
PubMed2000

Phosphorylation of recombinant human ATP:citrate lyase by cAMP-dependent protein kinase abolishes homotropic allosteric regulation of the enzyme by citrate and increases the enzyme activity. Allosteric activation of ATP:citrate lyase by phosphorylated sugars.

Recombinantly expressed human ATP:citrate lyase was purified from E. coli, and its kinetic behavior was characterized before and after phosphorylation. Cyclic AMP-dependent protein kinase catalyzed the incorporation of only 1 mol of phosphate per mole of enzyme homotetramer, and glycogen synthase kinase-3 incorporated an additional 2 mol of phosphate into the phosphorylated protein. Isoelectric focusing revealed that all of the phosphates were incorporated into only one of the four enzyme subunits. Phosphorylation resulted in a 6-fold increase in V(max) and the conversion of citrate dependence from sigmoidal, displaying negative cooperativity, to hyperbolic. The phosphorylated recombinant enzyme is more similar to the enzyme isolated from mammalian tissues than unphosphorylated enzyme with respect to the K(m) for citrate, CoA, and ATP, and the specific activity. Fructose 6-phosphate was found to be a potent activator (60-fold) of the unphosphorylated recombinant enzyme, with half-maximal activation at 0.16 mM, which results in a decrease in the apparent K(m) for citrate and ATP, as well as an increase in the V(max) of the reaction. Thus, human ATP:citrate lyase activity is regulated in vitro allosterically by phosphorylated sugars as well as covalently by phosphorylation.

ATP Citrate (pro-S)-Lyase↗
PubMed1993

Structure of a citrate double salt: potassium dihydrogen citrate-lithium potassium hydrogen citrate monohydrate.

The crystal structure of a double salt of potassium dihydrogen citrate and lithium potassium hydrogen citrate monohydrate has been determined. One potassium ion is coordinated with eight O atoms and the other with nine O atoms at M--O distances in the range 2.660 (1) to 3.139 (1) A. Two of these O atoms are shared by both potassium ions. The lithium ion is tetrahedrally surrounded by four O atoms at distances in the range 1.870 (3) to 1.988 (3) A. This crystal structure contains nine hydrogen bonds in the asymmetric unit. The water molecule connects different citrate ions along the c direction by hydrogen bonding.

Citrates↗
PubMed1986

Renal tissue citrate: independence from citrate utilization, reabsorption, and pH.

During alkalosis in vivo, renal tissue [citrate] [( citrate]t) increases and citrate reabsorption (Tcit) and utilization (Qcit) simultaneously decrease. The decrease in Qcit is interpreted to cause the increased [citrate]t, which in turn decreases Tcit X Renal citrate handling and [citrate]t could be regulated by other mechanisms, since alkalosis changes [substrate] and [H+] in extracellular (ECF) and intracellular (ICF) fluid. Also, since high plasma [citrate] decreases ionized [Ca2+] (Cai), it is not possible to determine in vivo whether there is a maximum for Tcit or Qcit and whether change in extracellular fluid (delta ECF) pH affects these maxima. We perfused the substrate-limited isolated rat kidney for either 110 (n = 36) or 50 min (n = 44) at pH 7.2, 7.4, or 7.6; pH was changed by varying [HCO3-]; Cai was held constant at approximately 2.5 meq/liter. When citrate was the only substrate available in a Krebs-Ringer-HCO3 perfusate containing 6% substrate-free albumin, both Qcit and Tcit had maximal rates: Qcit much greater than Tcit; at pH 7.6, Qcit and Tcit were significantly reduced below their values at pH 7.2 or 7.4. In contrast to in vivo observations, [citrate]t was not significantly increased at high ECF pH. To test whether [citrate]t in the perfused kidney can increase in alkalosis, 11 additional perfusions were done in the presence of glucose plus lactate plus malate but without added citrate: [citrate]t = 0.6 mumol X g-1 at pH 7.6 and 0.3 mumol X g-1 at pH 7.2 (P less than 0.01); no citrate was detectable in the perfusate, and urinary citrate excretion was negligible. Thus, in the isolated rat kidney, an increase in [citrate]t occurred in alkalosis and was derived from precursors and not from citrate in the ECF. Overall, when only citrate was available to the isolated kidney during alkalosis, a significant rise in [citrate]t did not occur, although Vmax for Tcit and Qcit decreased. These effects of alkalosis on Tcit are consistent with observations in brush-border vesicles, where divalent citrate is the preferential substrate for luminal Na+-coupled transport; by contrast, high ECF pH and [HCO-3] apparently decrease Qcit by a direct effect on the utilization of citrate.

Absorption↗
PubMed1984

Augmentation of renal citrate excretion by oral potassium citrate administration: time course, dose frequency schedule, and dose-response relationship.

The time course, dose frequency schedule, and dose-response relationship of the citraturic response to orally administered potassium citrate was examined in 22 normal volunteers and 21 patients with uric acid or calcium nephrolithiasis. The slow-release (wax matrix) preparation of potassium citrate produced a rapid and sustained rise in urinary citrate lasting for up to 12 hours following a single oral administration. Probably owing to this prolonged action, the slow-release preparation when given in a twice-daily or thrice-daily schedule at a dosage of 60 meq or 3.78 Gm citrate/day virtually eliminated the normally wide circadian fluctuation in urinary citrate and maintained urinary citrate at a higher, more constant level throughout the day. The liquid preparation of potassium citrate was less effective in this regard. However, the two preparations of potassium citrate caused an equivalent rise in total 24-hour urinary citrate. When 24-hour excretions of citrate were examined, urinary citrate was shown to reach its peak level by the second day of potassium citrate treatment and to return to the pretreatment level by the second day after the treatment was stopped. The rise in urinary citrate produced by treatment was directly proportional to the dose of potassium citrate. In most hypocitraturic patients with renal stones, potassium citrate 60 meq/day restored normal urinary citrate (greater than 320 mg/day).

Administration, Oral↗
PubMed1998

Characterisation of citrate and iron citrate uptake by cultured rat hepatocytes.

BACKGROUND/AIMS: The endogenous low molecular weight iron chelator, citrate, is considered to be an important contributor to iron transport and the liver the main site of uptake of iron citrate in subjects suffering from diseases of iron overload. Moreover, the citrate-metabolising enzyme, aconitase, is implicated in the regulation of cellular iron metabolism. This study was undertaken to determine the role of citrate and ferric citrate in the uptake of iron by rat hepatocytes. METHODS: Cultured rat hepatocytes were incubated (37 degrees C, 15 min) with 100 microM [14C]-citrate in the presence or absence of 1.0 microM 55Fe. Membrane-bound and intracellular radiolabel were separated by incubation with the general protease, Pronase. RESULTS: Our results suggest that ferric citrate uptake is mediated by a specific citrate binding site which exhibits a higher affinity for citrate in the presence of iron than in its absence. Citrate was internalised by hepatocytes, with at least 70% being oxidised to CO2 within 15 min. Citrate uptake was pH-dependent, did not require the presence of sodium and increased with increasing iron concentration. Metabolic energy, anion channels, the Na+, K+-ATPase and vesicle acidification do not appear to play a role in uptake of ferric citrate, but functional sulphydryl groups may be involved. CONCLUSIONS: The data suggest either that ferric citrate complexes with higher molar ratios of iron to citrate relative to the incubation medium are bound preferentially to the membrane, or that once citrate has delivered its iron to the membrane, the complex dissociates and the components are internalised separately.

Animals↗
PubMed2000

Renal citrate metabolism and urinary citrate excretion in the infant rat.

BACKGROUND: Although hypercalciuria has the same prevalence in children as adults, children rarely develop renal stones. This may be explained by a greater urinary citrate excretion in infants compared with adults. The present study examines the renal excretion of citrate and renal cortical citrate metabolism in infant and adult rats. METHODS: Adult male and newly weaned infant rats were acclimated to metabolic cages and fed synthetic diets. Urine was collected after two days, and renal cortical citrate metabolism was assayed. RESULTS: Infant rats had a lower plasma [HCO3-] and higher plasma [K+] and had a fourfold higher urinary citrate:creatinine ratio and a twofold higher concentration of citrate in their urine compared with adult rats. This higher urinary citrate excretion was not due to a difference in renal proximal tubular Na/citrate cotransporter activity, nor renal cortical citrate synthase or ATP citrate lyase activities in infants as compared with adults. However, infant rat kidneys had significantly lower mitochondrial aconitase (m-aconitase) activity. Renal cortical citrate concentrations were comparable in infant and adult rats. Manipulation of plasma [K+] to adult levels did not affect the higher urinary citrate excretion in infant rats. CONCLUSIONS: Urinary citrate excretion in infant rats is greater than in adults but does not parallel tissue [citrate]. Thus, this higher urinary citrate is likely due to maturational differences in the proximal tubule, other than Na/citrate cotransport, that directly affect citrate transport.

Aging↗
PubMed1996

Regional hemodialysis anticoagulation: hypertonic tri-sodium citrate or anticoagulant citrate dextrose-A.

Regional citrate anticoagulation should be a simple process of substituting hypertonic (1.6 mol/L) citrate for heparin and adjusting the infusion to obtain an arterial activated clotting time of 150 to 200 seconds. Serious, documented complications of citrate anticoagulation involve citrate intoxication during isolated ultrafiltration; hyperaluminemia, hyperammonemia, and hypernatremia during sorbent dialysis; and profound alkalosis, paresthesias, arrhythmia, and cardiac arrest during bicarbonate dialysis. We suspected that some of these complications could be avoided by using anticoagulant citrate dextrose-A (ACD) rather than hypertonic tri-sodium citrate (TSC) as the anticoagulant. In a cross-over study with random assignment order eight adults underwent mid-week dialyses with ACD (0.113 mol/L citrate) and TSC (1.6 mol/L citrate) regional citrate anticoagulation. Predialysis to postdialysis changes in Na (mEq/L), Ca (mg/dL), ionized Ca (mg/dL), pH, and HCO3 (mEq/L) are listed below. [Table in journal] Using continuous blood flow and avoiding isolated ultrafiltration and sorbent dialysis should prevent the delivery system complications of regional citrate anticoagulation. During this evaluation isotonic and hypertonic citrate resulted in similar serum sodium changes, and standard dialysate effectively reversed the citrate/calcium interaction of both hypertonic and isotonic citrate infusions to restore homeostasis without a separate calcium infusion. The combination of TSC and bicarbonate dialysate does produce a profound metabolic alkalosis, which is lessened by using ACD. In general, regional citrate anticoagulation is simplified by using standard dialysate with a hypertonic rather than an isotonic citrate infusion, and dangerous complications are further evaded by adjusting the dialysate bicarbonate to 25 to 30 mmol/L or substituting a mixture of citric acid and TSC (ACD) for TSC.

Adult↗
PubMed1994

Uniport of anionic citrate and proton consumption in citrate metabolism generates a proton motive force in Leuconostoc oenos.

The mechanism and energetics of citrate transport in Leuconostoc oenos were investigated. Resting cells of L. oenos generate both a membrane potential (delta psi) and a pH gradient (delta pH) upon addition of citrate. After a lag time, the internal alkalinization is followed by a continuous alkalinization of the external medium, demonstrating the involvement of proton-consuming reactions in the metabolic breakdown of citrate. Membrane vesicles of L. oenos were prepared and fused to liposomes containing cytochrome c oxidase to study the mechanism of citrate transport. Citrate uptake in the hybrid membranes is inhibited by a membrane potential of physiological polarity, inside negative, and driven by an inverted membrane potential, inside positive. A pH gradient, inside alkaline, leads to the accumulation of citrate inside the membrane vesicles. Kinetic analysis of delta pH-driven citrate uptake over a range of external pHs suggests that the monovalent anionic species (H2cit-) is the transported particle. Together, the data show that the transport of citrate is an electrogenic process in which H2cit- is translocated across the membrane via a uniport mechanism. Homologous exchange (citrate/citrate) was observed, but no evidence for a heterologous antiport mechanism involving products of citrate metabolism (e.g., acetate and pyruvate) was found. It is concluded that the generation of metabolic energy by citrate utilization in L. oenos is a direct consequence of the uptake of the negatively charged citrate anion, yielding a membrane potential, and from H(+)-consuming reactions involved in subsequent citrate metabolism, yielding a pH gradient. The uptake of citrate is driven by its own concentration gradient, which is maintained by efficient metabolic breakdown (metabolic pull).

Anions↗
PubMed1983

Dependence of ATP-citrate lyase kinase activity on the phosphorylation of ATP-citrate lyase by cyclic AMP-dependent protein kinase.

ATP-citrate lyase from rat liver and adipose tissue is phosphorylated by either ATP-citrate lyase kinase or catalytic subunit of cyclic AMP-dependent protein kinase to 0.5-0.6 mol/subunit. We previously demonstrated that the site phosphorylated by ATP-citrate lyase kinase (peptide B) is different from that phosphorylated by catalytic subunit of cyclic AMP-dependent protein kinase (peptide A) (Ramakrishna, S., Pucci, D. L., and Benjamin, W.B. (1981) J. Biol. Chem. 256, 10213-10216). ATP-citrate lyase phosphorylation by both protein kinases added simultaneously was increased synergistically. When ATP-citrate lyase was first phosphorylated by catalytic subunit of cyclic AMP-dependent protein kinase, the net phosphorylation of the fragments subsequently phosphorylated by lyase kinase increased about 6-fold. However, when ATP-citrate lyase was first phosphorylated by lyase kinase, there was no effect on the subsequent phosphorylation of the enzyme by cyclic AMP-dependent protein kinase. Alkaline phosphatase-dephosphorylated ATP-citrate lyase was phosphorylated by catalytic subunit of cyclic AMP-dependent protein kinase to 0.9-1.0 mol/subunit. However, dephospho-ATP-citrate lyase was not phosphorylated by lyase kinase. The addition of both protein kinases simultaneously phosphorylated ATP-citrate lyase up to 2 mol/subunit. Phosphorylation of dephospho-ATP-citrate lyase first by catalytic subunit of cyclic AMP-dependent protein kinase and ATP enabled the lyase to be phosphorylated by lyase kinase. Peptide mapping and phosphoamino acid analysis of dephospho-ATP-citrate lyase phosphorylated by catalytic subunit of cyclic AMP-dependent protein kinase and/or lyase kinase conclusively showed that phosphorylation of ATP-citrate lyase by ATP-citrate lyase kinase was completely dependent on peptide A phosphorylation by cyclic AMP-dependent protein kinase. Furthermore, increased phosphorylation when both protein kinases were added simultaneously was due to increased phosphorylation at peptide B.

ATP Citrate (pro-S)-Lyase↗