Purification and some kinetic properties of rat liver ATP citrate lyase.

A new purification procedure for rat liver ATP citrate lyase is described. The method reproducibly gives homogenous undegraded enzyme. Steady-state kinetic analysis of ATP citrate lyase was complicated by the presence of ADP, a product of the reaction, in solutions of ATP. The kinetic patterns observed were dependent on whether ADP was removed by the assay system. When assays were performed with a method in which ADP was removed, the results showed that the enzyme obeys a double-displacement mechanism with a phosphoenzyme intermediate. This resolves a controversy between the results of previous kinetic studies and those of isotope-exchange and enzyme-labelling experiments.     

Purification and properties of citrate lyase from Streptococcus diacetilactis.

Citrate lyase from Streptococcus diacetilactis has been purified to yield a protein that was homogeneous as judged by sedimentation velocity and sedimentation equilibrium experiments. The enzyme's sedimentation coefficient is 16.8 S and its molecular weight is around 585,000. It contains three nonidentical subunits of about 53,000, 34,000, and 10,000 daltons. The enzyme in its active form contains an acetyl group which turns over during the citrate cleavage reaction. Removal of the acetyl group inactivates the enzyme. The deacetyl enzyme can be partially reactivated by acetylation with acetic anhydride. The enzyme undergoes slow "reaction-inactivation." The rate of inactivation is first order and the rate constant of inactivation is much lower than that for a similar inactivation process of the citrate lyase from Klebsiella aerogenes. Like the latter enzyme it contains stoichiometric amounts of phosphopantothenate. The enzyme is inactivated at pH greater than 8.1 and the presence of citrate provides protection against this inactivation. Sedimentation studies of the enzyme at pH 8.7 indicate that the enzyme is dissociated, which may account for the inactivation. The enzyme is immunologically different from citrate lyases of K. aerogenes and Escherichia coli.     

Purification and characterization of ATP:citrate lyase from Hydrogenobacter thermophilus TK-6.

ATP:citrate lyase [ATP citrate (pro-3S)-lyase; EC 4.1.3.8] was purified and characterized from the cells of Hydrogenobacter thermophilus, an aerobic, thermophilic, hydrogen-oxidizing bacterium which fixes carbon dioxide by a reductive carboxylic acid cycle. The enzyme was quite stable, even in the absence of sulfhydryl reagents. Optimum pH for reaction was 6.7 to 6.9, and optimum temperature was around 80 degrees C. The molecular weight of native enzyme was estimated to be 260,000 by gel filtration analysis, and that of a subunit was estimated to be 43,000 by sodium dodecyl sulfate-polyacrylamide gel analysis. Km values for reaction components were as follows: citrate, 6.25 mM; ATP, 650 microM; coenzyme A, 40.8 microM; and Mg2+, 8 mM. The enzyme showed citrate synthase activity in the presence of Mg2+, but the reaction rate was very low (less than 1/200 of the lyase activity).     

Purification and properties of citrate lyase from Escherichia coli

Citrate lyase (EC 4.1.3.6) has been purified from Escherichia coli and the homogeneity of the preparation established from the three-component subunits obtained on sodium dodecyl sulfate/polyacrylamide gel electrophoresis. The purified enzyme has a specific activity of 120 mumol min-1 mg-1 and requires optimally 10 mM Mg2+ and a pH of 8.0 for the cleavage reaction. The native enzyme is polydispersed in the ultracentrifuge and in polyacrylamide gel electrophoresis. The enzyme complex is composed of three different polypeptide chains of 85 000, 54 000, 32 000 daltons. An estimate of subunit stoichiometry indicates that 1 mol of the largest polypeptide chain is associated with 6 mol each of the smaller ones. The polypeptide subunits have been isolated in pure state and their biological functions characterize. The 54 000-dalton subunit functions as the acyltransferase alpha subunit catalyzing the formation of citryl coenzyme A from citrate in the presence of acetyl coenzyme A and ethylenediaminetetraacetic acid. The 32 000-dalton subunit functions as the acyllyase beta subunit catalyzing the cleavage of (3S)-citryl coenzyme A to oxal-acetate and acetyl coenzyme A. The 85 000-dalton subunit, which carries exclusively the prosthetic group components, functions as the acyl-carrier protein gamma subunit in the cleavage of citrate in the presence of mg2+ and the alpha and beta subunits. The presence of a large ACP subunit and the unusual stoichiometry of the different subunits distinguish the complex from other citrate lyases. A ligase which acetylates the deacetyl[citrate lyase] in the presence of acetate and ATP has ben shown to be present in the organism.(ABSTRACT TRUNCATED AT 250 WORDS)     

ATP:citrate lyase of Rhodotorula gracilis: purification and properties

ATP:citrate lyase was purified from the oleaginous yeast Rhodotorula gracilis to homogeneity as judged by polyacrylamide gel electrophoresis, using a novel citrate-Sepharose procedure. The enzyme was found to have a molecular weight of 520,000 and consisted of four identical subunits (Mr = 120,000). Two minor low molecular weight bands were observed on SDS-PAGE (Mr 51,000 and 49,000). Trypsin digestion experiments indicated that these could have been the result of limited proteolysis by an endogenous trypsin-like proteinase. In this respect, it resembles the mammalian ATP:citrate lyase. The enzyme was stimulated by NH+4 ions and inhibited by palmitoyl, lauroyl, oleoyl, myristoyl and stearoyl-CoA esters, glutamate and glucose 6-phosphate but not by acetyl-CoA or shorter chain fatty acyl-CoA esters. The enzyme exhibited normal Michaelis-Menten kinetics for citrate; however there was a 3-fold increase in Km with a high concentration of Cl- ions (0.25 M). The possible regulatory roles of ATP:citrate lyase in R. gracilis are discussed in the light of these findings.     

Characterization of ATP citrate lyase from Chlorobium limicola.

ATP citrate lyase (EC 4.1.3.8) from Chlorobium limicola was partially purified. It was established that the consumption of substrates and the formation of products proceeded stoichiometrically and that citrate cleavage was of the si-type. ADP and oxaloacetate inhibited enzyme activity. Oxaloacetate also inhibited the growth of C. limicola.     

The distinctiveness of ATP:citrate lyase from Aspergillus nidulans

ATP:citrate lyase (ACL), an important enzyme in lipid synthesis, has been purified from Aspergillus nidulans to a specific activity of 19.6 micromol min(-1) mg(-1), almost twice that of any other purified ACL and shown to be distinct from any previously purified ACL. The enzyme is a 371+/-31 kDa hexamer of 3 alpha, 3 beta proteins, unlike the 4 alpha tetramer found in rats or yeasts. The molecular weights of the alpha and beta protein subunits were determined by SDS-PAGE to be 70 and 55 kDa.ACL in A. nidulans (unlike Aspergillus niger) appears to be regulated by the carbon source present in the media. In crude extracts, it was found at high activity (88 micromol min(-1) mg protein(-1)) in glucose-grown cells but only at low activity (10 micromol min(-1) mg protein(-1)) in acetate-grown cells.     

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.     

Compartmentation of ATP:citrate lyase in plants

Extracts prepared from young leaves of Pea (Pisum sativum), tobacco (Nicotiana tabacum), rape (Brassica napus), and spinach (Spinacia oleracea) all contained ATP:citrate lyase (ACL) activity, which was most active in rape leaflets (130 nmol min(-1) g fresh weight). In rape and spinach, ACL activity was predominantly localized in the plastids (between about 78% and 90% of the total activity), whereas in pea and tobacco, distribution was mainly cytosolic (about 85% and 78%, respectively, of the total). These distributions were calculated from the relative distributions of plastid and cytosol marker enzymes. Cross-reactivity between plant and rat ACL antibody was carried out by immunoblot analysis and, in rape and spinach, showed that a 120-kD protein, presumably indicating homomeric ACL proteins, was present in both cytosolic and plastidic fractions. In pea, two cross-reacting proteins were detected, the major material being in the cytosol fraction. Therefore, ACL occurs both in the cytosol and plastids of higher plants, but the distribution of activity changes according to the species. The plastidic ACL is proposed to function for the supply of acetyl-coenzyme A for lipid biosynthesis de novo, whereas the cytosolic ACL may provide acetyl-coenzyme A for the mevalonate pathway or fatty acid elongation.     

Glucose- and insulin-independent induction of ATP citrate lyase in primary cultures of rat hepatocytes.

ATP citrate lyase, which is involved in the translocation of the lipogenic precursor acetyl-CoA from mitochondria to cytosol, was studied in primary cultures of hepatocytes from adult rats. After an initial decrease at the first day of culture the enzyme activity was nearly constant during the following days. It could be enhanced between 24h and 48 h in culture about 1.5-fold by elevation of the insulin concentration to 10-7mol/1.22-fold by elevation of the glucose concentration from 5 to 25 mmol/l and 3.5-fold by simultaneous elevation of insulin and glucose. The increase of activity was about linear with time for 24 h and could be blocked by cycloheximide, which inhibits protein synthesis at the translational level. Both observations suggest that the enhancement of activity was due to induction rather than to activation by interconversion. The glucose-dependent induction was furthermore evidenced by immunotitration which indicated a parallel increase of activity and enzyme protein.     

Radicicol binds and inhibits mammalian ATP citrate lyase

Six different biotinylated radicicol derivatives were synthesized as affinity probes for identification of cellular radicicol-binding proteins. Derivatives biotinylated at the C-17 (BR-1) and C-11 (BR-6) positions retained the activity of morphological reversion in v-src-transformed 3Y1 fibroblasts. Two radicicol-binding proteins, 120 and 90-kDa in size, were detected in HeLa cell extracts by employing BR-1 and BR-6, respectively. The 90-kDa protein bound to BR-6 was identified to be Hsp90 by immunoblotting. The 120-kDa protein bound to BR-1 was purified from rabbit reticulocyte lysate, and its internal amino acid sequence was identical to that of human and rat ATP citrate lyase. The identity of the 120-kDa protein as ATP citrate lyase was confirmed by immunoblotting. Interaction between BR-1 and ATP citrate lyase was blocked by radicicol but not by herbimycin A that interacts with Hsp90. These results suggest that radicicol binds the two proteins through different molecular portions of its structure. BR-1-bound ATP citrate lyase isolated from rabbit reticulocyte lysate showed no enzymatic activity. The activity of rat liver ATP citrate lyase was inhibited by radicicol and BR-1 but not by BR-6. Kinetic analysis demonstrated that radicicol was a non-competitive inhibitor of ATP citrate lyase with K(i) values for citrate and ATP of 13 and 7 microm, respectively.     

Purification and properties of polyphosphoinositide phosphomonoesterase from rat brain.

1. On subcellular fractionation of rat brain homogenate, polyphosphoinositide phosphomonoesterase activity was greater in the cytosol than the membranous fractions. 2. The enzyme was purified from the cytosol by column chromatography on DEAE-cellulose, calcium phosphate gel and Sephadex G-100. 3. The final preparation of the enzyme showed a 430-fold purification over the whole homogenate and appeared to be homogeneous since it gave a single band on sodium dodecyl sulphate-polyacrylamide gel electrophoresis and on isoelectric focusing. The enzyme has a relatively low molecular weight and an isoelectric point of 6.8. 4. The phosphatase showed a high affinity for triphosphoinositide. Without added Mg2+, the Km was 25 muM and V was 33 mumol Pi released/min/mg protein. 5. The enzyme hydrolysed diphosphoinositide at a slower rate than triphosphoinositide. In the presence of 10 mM Mg2+, the Km values for triphosphoinositide and diphosphoinositide were 5 muM and 25 muM respectively and V was the same for each substrate. 6. Both Mg2+ and Ca2+ activated the enzyme. While Ca2+ produced maximum activation at 100 muM, a much higher concentration of Mg2+ (10 mM) was required to elicit comparable activation. The enzyme did not show an absolute requirement for Mg2+ or Ca2+ as it exhibited low activity in the presence of 0.5 mM EDTA or EGTA. 7. The phosphatase showed maximum activity between 7.4 and 7.6. A drop in pH to 7.0 activated it almost completely, whereas an increase in pH to 8.0 halved the activity. 7.0 activated it almost completely, whereas an increase in pH to 8.0 halved the activity.