Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:6.4.1.2 (acetyl-CoA carboxylase)
2,876 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effects of Triton WR 1339, starvation and cholesterol diet on the activities of 3-hydroxy-3-methylglutaryl-CoA reductase (HMG-CoA reductase) and acetyl-CoA carboxylase and on the rates of mevalonic acid (MVA) biosynthesis from acetyl-CoA and malonyl-CoA in the soluble (140 000 g) and microsomal fractions of rat liver, on the rate of incorporation of these substrates into squalene, cholesterol and lanosterol in the rat liver postmitochondrial fraction and on the rate of fatty acid biosynthesis was studied. The administration of Triton WR 1339 (200 mg per 100 g of body weight twice) stimulated the activity of HMG-CoA reductase and MVA biosynthesis from acetyl-CoA and malonyl-CoA in the intact and solubilized microsomal fractions and had no effect on these parameters in the soluble fraction. Starvation for 36 hrs did not cause inhibition of the reductase activity or MVA biosynthesis from both substrates in the soluble fraction. Alimentary cholesterol significantly increased the activity of HMG-CoA reductase, had no effect on the rate of MVA biosynthesis from acetyl-CoA and stimulated the malonyl-CoA incorporation in to MVA in the soluble fraction. Starvation an alimentary cholesterol inhibited the HMG-CoA reductase activity and MVA biosynthesis from both substrates in the solubilized microsomal fraction. Triton WR 1339 stimulated 4--19-fold the lipid formation in the total unsaponified fraction and its components i.e. squalene, lanosterol, cholesterol, from acetyl-CoA and only insignificantly (1,2--1,7-fold) increased malonyl-CoA incorporation into these compounds. Starvation and alimentary cholesterol repressed lanosterol and cholesterol biosynthesis from acetyl-CoA, decreased malonyl-CoA incorporation into these sterols and had no influence on squalene biosynthesis from the two substrates. Triton WR 1339 and starvation inhibited the acetyl-CoA carboxylase activity, unaffected by alimentary cholesterol. No significant changes in the rate of fatty acid biosynthesis from the substrates were observed. The data obtained provide evidence for the existence of autonomic pathways of MVA biosynthesis localized in the soluble and microsomal fractions of rat liver. The pathway of MVA biosynthesis in the soluble fraction is less sensitive to regulatory factors. Sterol biosynthesis from malonyl-CoA is also more resistant to regulatory effects than sterol biosynthesis from acetyl-CoA. This suggests that HMG-CoA reductase localized in the soluble fraction takes part in MVA and sterol biosynthesis from malonyl-CoA.
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PMID:[Activities of 3-hydroxyl-3-methylglutaryl-CoA reductase and acetyl-CoA carboxylase and the rate of mevalonic acid, squalene, sterol and fatty acid biosynthesis from [1-14C]acetyl-CoA and [2-14C]malonyl-CoA in rat liver: effects of Triton WR 1339, starvation and cholesterol diet]. 611 54

Fatty acid synthesis is traditionally viewed as being confined to the cytosolic cellular fraction, although a substantial body of data indicates that both microsomes and mitochondria are capable of initiating fatty acid synthesis and may contain acetyl-CoA carboxylase [acetyl-CoA:carbon-doxide ligase (ADP-forming), EC 6.4.1.2], fatty acid synthetase, and ATP-citrate lyase [ATP citrate (pro-3S)-lyase; ATP:citrate oxaloacetate-lyase (pro-3S-CH2COO- leads to acetyl-CoA; ATP-dephosphorylating), EC 4.1.3.8] activities. We have identified 32P-labeled acetyl-CoA carboxylase and 32P-labeled ATP-citrate lyase by immunoprecipitation of a rat hepatocyte microsomal preparation. In the transition between the fasting state (low rates of lipogenesis) and fasting/re-feeding (high rates), the fraction of total cytosolic plus microsomal acetyl-CoA carboxylase in the microsomes increases from 6% to 43%, whereas the microsomal proportion of total fatty acid synthetase and ATP-citrate lyase remains approximately 10%. Microsome isolation conditions favoring carboxylase polymerization (presence of citrate) promote microsomal association, whereas conditions favoring enzyme protomerization (malonyl-CoA, preincubation with cyclic AMP/ATP/Mg2+) diminish this association. The microsomal enzyme has a 5-fold higher specific activity than the cytosolic enzyme as determined by immunotitration. Sucrose density gradient analysis of the microsomal fraction indicates that a substantial portion of carboxylase activity sediments with marker enzymes for endoplasmic reticulum, plasma membrane, Golgi apparatus, and outer mitochondrial membrane, while cytosolic enzyme or isolated enzyme incubated under polymerizing conditions does not penetrate the gradient. These data suggest that the microsomes may be a significant locus of fatty acid synthesis initiated with association of acetyl-CoA carboxylase polymer with this fraction.
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PMID:Microsomal acetyl-CoA carboxylase: evidence for association of enzyme polymer with liver microsomes. 611 83

Biotin-binding antibodies were raised in rabbits by injecting biotin-bovine serum albumin conjugate. Neither the protomer nor the polymer of rat mammary-gland acetyl-CoA carboxylase formed precipitin bands with the anti-biotin. By virtue of its ability to bind biotin (apparent binding constant for free biotin about 1mum), the anti-biotin inhibited the carboxylase activity under certain conditions. This property of the antibody was employed to detect the ligand-induced changes affecting the biotinyl group in different conformational states of mammalian carboxylase. Depending on the ligand present, the biotinyl group in the protomeric form was either accessible or inaccessible to the antibody. The biotinyl group of the protomer generated by a relatively high concentration of NaCl (0.5m) reacted with the antibody, and the antibody-carboxylase complex could not be converted into active enzyme by citrate. Further experiments showed that citrate failed to induce polymerization in this protomer-antibody complex and that anti-biotin could be displaced rapidly from this complex with excess of biotin. The resulting protomer was converted into the polymeric state on citrate addition, with parallel regain of enzyme activity. In the presence of ADP+Mg(2+), ATP+Mg(2+) or ATP+Mg(2+)+HCO(3) (-), however, the enzyme remained as a protomer, but its configuration was such that the biotinyl group was essentially inaccessible to the antibody. Likewise, the biotinyl group of the different polymeric forms of the carboxylase (s approximately 30-45S) engendered by phosphate, malonyl-CoA, acetyl-CoA or citrate remained essentially inaccessible, since their activity was minimally affected by the anti-biotin. In the presence of 0.15m-NaCl, the phosphate-induced polymer reverted to a approximately 19S form with concomitant appearance of anti-biotin-sensitivity, whereas the other polymeric forms remained unaffected under similar experimental conditions.
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PMID:Detection of ligand-induced perturbations affecting the biotinyl group of mammalian acetyl-coenzyme A carboxylase by using biotin-binding antibodies. 611 76

Ketone bodies accumulate in the plasma in conditions of fasting and uncontrolled diabetes. The initiating event is a change in the molar ratio of glucagon:insulin. Insulin deficiency triggers the lipolytic process in adipose tissue with the result that free fatty acids pass into the plasma for uptake by liver and other tissues. Glucagon appears to be the primary hormone involved in the induction of fatty acid oxidation and ketogenesis in the liver. It acts by acutely dropping hepatic malonyl-CoA concentrations as a consequence of inhibitory effects exerted in the glycolytic pathway and on acetyl-CoA carboxylase (EC 6.4.1.2). The fall in malonyl-CoA concentration activates carnitine acyltransferase I (EC 2.3.1.21) such that long-chain fatty acids can be transported through the inner mitochondrial membrane to the enzymes of fatty acid oxidation and ketogenesis. The latter are high-capacity systems assuring that fatty acids entering the mitochondria are rapidly oxidized to ketone bodies. Thus, the rate-controlling step for ketogenesis is carnitine acyltransferase I. Administration of food after a fast, or of insulin to the diabetic subject, reduces plasma free fatty acid concentrations, increases the liver concentration of malonyl-CoA, inhibits carnitine acyltransferase I and reverses the ketogenic process.
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PMID:The regulation of ketogenesis. 612 45

The kinetics of citrate-induced activation and polymerization (into filaments) of the 450,000-dalton protomeric form of acetyl-CoA carboxylase were compared to assess the concertedness of the two processes. Rapid-quench techniques were employed to measure the time course of activation by citrate of the carboxylase-catalyzed reaction. When enzyme was preincubated with citrate prior to initiating the steady state turnover reaction with acetyl-CoA in the rapid-quench device, the observed rate of carboxylation of acetyl-CoA was apparently linear from the moment of mixing. However, when enzyme was mixed with citrate to initiate the reaction, a lag (t1/2 = 0.7 s) occurred in the approach to steady state carboxylation rate. This lag was independent of enzyme concentration over a 230-fold range and was marginally dependent upon citrate concentration. Over the same range of enzyme concentration, polymerization of carboxylase protomers, as determined by right angle light scattering, was enzyme concentration-dependent in a manner predicted by a single protomer activation step, followed by a rate-limiting dimerization of active protomer and subsequent polymerization. Based on these results, it is concluded that activation of catalysis and the polymerization of carboxylase protomers are not concerted. Furthermore, activation of carboxylation leading to the formation of an active protomer was faster than polymerization under all conditions, and therefore precedes polymerization. It was also shown that the activation constant (Kact) for citrate is altered in a predictable manner by the accumulation of the reaction product, malonyl-CoA, the Kact increasing with increasing malonyl-CoA concentration. Additional evidence is presented indicating that this change in Kact was not caused by autophosphorylation of the enzyme under these conditions and that phosphorylation does not affect the mechanism of activation elucidated above.
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PMID:Kinetics of activation of acetyl-CoA carboxylase by citrate. Relationship to the rate of polymerization of the enzyme. 613 55

Citrate, an allosteric activator of acetyl-CoA carboxylase, induces polymerization of an inactive protomeric form of the enzyme into an active filamentous form composed of 10-20 protomers. The light-scattering properties of the carboxylase were used to study the kinetics of its polymerization and depolymerization. From stopped flow kinetic studies, we have established that polymerization is a second order process, with a second order rate constant of 597,000 M-1 s-1. There appear to be two steps which limit polymerization of the inactive carboxylase protomer: 1) a rapid citrate-induced conformational change which is independent of enzyme concentration and leads to an active protomeric form of the enzyme (Beaty, N. B., and Lane, M. D. (1983) J. Biol. Chem. 258, 13043-13050, preceding paper) and 2) the dimerization of the active protomer, which constitutes the first step of polymerization and is enzyme concentration-dependent. Dimerization is the rate-limiting step of acetyl-CoA carboxylase polymerization. Depolymerization of fully polymerized acetyl-CoA carboxylase is caused by malonyl-CoA, ATP X Mg, and Mg2+. Both malonyl-CoA and ATP X Mg (and HCO-3) compete with citrate in the maintenance of a given state of the protomer-polymer equilibrium apparently by carboxylating the enzyme to form enzyme-biotin-CO-2 which destablizes the polymeric form. Free citrate is the species responsible for polymerizing the enzyme and Mg2+ causes depolymerization of the enzyme by lowering the concentration of free citrate.
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PMID:The polymerization of acetyl-CoA carboxylase. 613 56

The activity of acetyl-CoA carboxylase, measured in various ways, was studied in 15000g extracts of rat liver hepatocytes and compared with the rate of fatty acid synthesis in intact hepatocytes incubated with insulin or glucagon. Hepatocyte extracts were prepared by disruption of cells with a Dounce homogenizer or by solubilization with 1.5% (v/v) Triton X-100. Sucrose-density-gradient centrifugation demonstrated that the sedimentation coefficient of acetyl-CoA carboxylase from cell extracts was 30-35S, regardless of the conditions of incubation or disruption of hepatocytes. Solubilization of cells with 1.5% Triton X-100 yielded twice as much enzyme activity (measured by [14C]bicarbonate fixation) in the sucrose-gradient fractions as did cell disruption by the Dounce homogenizer. Analysis by high-performance liquid chromatography of acetyl-CoA carboxylase reaction mixtures showed that [14C]malonyl-CoA accounted for 10-60% of the total acid-stable radioactivity, depending on the method for disrupting hepatocytes and on the preincubation of the 15000g extract, with or without citrate, before assay. Under conditions in which incubation of cells with insulin or glucagon caused an activation or inhibition, respectively, of acetyl-CoA carboxylase, only 25% of the acid-stable radioactivity was [14C]malonyl-CoA and enzyme activity was only 13% (control), 16% (insulin), and 57% (glucagon) of the rate of fatty acid synthesis. Under conditions when up to 60% of the acid-stable radioactivity was [14C]malonyl-CoA and acetyl-CoA carboxylase activity was comparable with the rate of fatty acid synthesis, there was no effect of insulin or glucagon on enzyme activity.
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PMID:Studies on the assay, activity and sedimentation behaviour of acetyl-CoA carboxylase from isolated hepatocytes incubated with insulin or glucagon. 614 77

Rat mammary gland acetyl-CoA carboxylase (acetyl-CoA:carbon dioxide ligase (ADP forming), EC 6.4.1.2) is rapidly and irreversibly inactivated by micromolar concentrations of S-(4-bromo-2,3-dioxobutyl)-CoA (BDB-CoA) or p-hydroxymercuribenzoate (PHMB). Inhibition of both half reactions (i.e., the biotin carboxylation and the carboxyltransferase) catalyzed by acetyl-CoA carboxylase closely parallels loss in overall activity (malonyl-CoA synthesis). The presence of a substrate or product (acetyl-CoA, ATP, ADP, Pi) or inhibitor (palmitoyl-CoA) does not protect the enzyme from inhibition caused by BDB-CoA or PHMB. On the other hand, citrate, an activator of acetyl-CoA carboxylase, affords substantial protection against inhibition by BDB-CoA and PHMB. Covalent modification by BDB-CoA or PHMB appears to lock acetyl-CoA carboxylase in an inactive conformation (15-30 S) that is unable to undergo citrate-induced self-association into the catalytically competent polymeric form.
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PMID:Inhibitory effects of sulfhydryl reagents on acetyl-CoA carboxylase from rat mammary gland. 614 6

The subcellular distribution of acetyl-CoA carboxylase [acetyl-CoA-carbon dioxide ligase (ADP-forming), EC 6.4.1.2] was determined in mesophyll protoplasts isolation from barley, a C3 plant, and sorghum, a C4 plant. In both species, all of the mesophyll acetyl-CoA carboxylase was demonstrated to be chloroplastic. In barley leaves and mesophyll protoplasts, a single biotinyl protein of 60,000 Da was identified by a modified Western-blotting procedure. The subcellular distribution of this biotinyl protein was identical to that found for acetyl-CoA carboxylase. These results are discussed in relation to the compartmentation of reactions requiring malonyl-CoA as a substrate.
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PMID:Subcellular distribution of acetyl-coenzyme A carboxylase in mesophyll cells of barley and sorghum leaves. 615 78

The effect of hypolipidemic drugs, WY14643 and DH990, on plant lipid metabolism has been studied. The total incorporation of [14C]acetate into lipids was inhibited by addition of both drugs to aged potato (Solanum tuberosum) tuber discs, spinach (Spinacia oleracea) leaves, and spinach chloroplasts, while the incorporation in Chlorella vulgaris cells was affected only by DH990. Moreover, DH990 inhibited the incorporation of 14C-labeled fatty acids into phosphatidylcholine and phosphatidylethanolamine of potato discs, and decreased the incorporation into phosphatidylglycerol of Chlorella cells. DH990 inhibited the formation of polyunsaturated fatty acids in potato discs, Chlorella cells, and spinach leaves, whereas WY14643 had no effect on the formation of these fatty acids. Stearoyl-ACP desaturase from safflower (Carthamus tinctorius) seeds was very sensitive to both drugs, especially DH990, which completely blocked the activity at 2 mM levels. When safflower lysophospholipid acyltransferases were solubilized by detergent treatment, only DH990 inhibited the incorporation of [14C]oleoyl-CoA into lysophosphatidylcholine or lysophosphatidylethanolamine. Both drugs inhibited fatty acid synthesis from [14C]malonyl-CoA in the microsomal fraction from safflower seeds, but only DH990 inhibited FAS activity in the soluble fraction; both drugs inhibited severely the formation of stearic acid. Both acetyl-CoA carboxylase and acetyl-CoA synthetase were sensitive to both drugs.
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PMID:The effect of hypolipidemic drugs on plant lipid metabolism. 648 26


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