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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)

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

We have investigated several factors which influence acetyl-CoA carboxylase (ACCase) activity in lysed spinach chloroplasts. (1) When assayed after rapid lysis of light-incubated chloroplasts, ACCase activity was 2-fold higher than activity from dark-incubated chloroplasts. Within 5 min after lysis, activity from dark-incubated chloroplasts increased, suggesting a transient inactivation or inhibition of ACCase in the dark. (2) When lysed chloroplast suspensions were incubated with 30 to 100 microM acetyl-CoA before starting assays, activity was 4-fold higher than if suspensions were not preincubated with acetyl-CoA. CoA, malonyl-CoA, propionyl-CoA, and butyryl-CoA also activated ACCase. Full acetyl-CoA activation required MgATP and was essentially complete after 8 min. ACCase activity decreased upon removal of acetyl-CoA by gel filtration and was partially restored by readdition of acetyl-CoA. Thus, ACCase activation by acetyl-CoA was reversible. (3) Dithiothreitol and thioredoxin stimulated ACCase activity, but only in preparations where ACCase activity was low. (4) ACCase was assayed in concentrations of ATP, ADP, NADPH, NADP+, Mg2+, and CO2/HCO-3, which are estimated to occur in the stroma of chloroplasts under illumination or darkness. ACCase activity from lysed chloroplast suspensions was 10-fold higher when illuminated conditions were used. However, this activity was still 5-fold to 10-fold lower than the rates required to sustain known in vivo rates of fatty acid synthesis and in vitro rates achieved under optimum assay conditions with saturating substrates.
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PMID:Regulation of spinach chloroplast acetyl-CoA carboxylase. 980 58

Biotin is an essential cofactor for a small number of enzymes involved mainly in the transfer of CO2 during HCO-3-dependent carboxylation reactions. This review highlights progress in plant biotin research by focusing on the four major areas of recent investigation: the structure, enzymology, and localization of two important biotinylated proteins (methylcrotonoyl-CoA carboxylase involved in the catabolism of leucine and noncyclic isoprenoids; acetyl-CoA carboxylase isoforms involved in a number of biosynthetic pathways); the biosynthesis of biotin; the biotinylation of biotin-dependent carboxylases, including the characterization of biotin holocarboxylase synthetase isoforms; and the detailed characterization of a novel, seed-specific biotinylated protein. A central challenge for plant biotin research is to determine in molecular terms how plant cells regulate the flow of biotin to sustain the biotinylation of biotin-dependent carboxylases during biosynthetic reactions.
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PMID:BIOTIN METABOLISM IN PLANTS. 1501 85

Acetyl-CoA carboxylase from the diatom Cyclotella cryptica has been purified to near homogeneity by the use of ammonium sulfate fractionation, gel filtration chromatography, and affinity chromatography with monomeric avidin-agarose. The specific activity of the final preparation was as high as 14.6 micromoles malonyl-CoA formed per milligram protein per minute, indicating a 600-fold purification. Native acetyl-CoA carboxylase has a molecular weight of approximately 740 kilodaltons and appears to be composed of four identical biotin-containing subunits. The enzyme has maximal activity at pH 8.2, but enzyme stability is greater at pH 6.5. K(m) values for MgATP, acetyl-CoA, and HCO(3)- were determined to be 65, 233, and 750 micromolar, respectively. The purified enzyme is strongly inhibited by palmitoyl-CoA, and is inhibited to a lesser extent by malonyl-CoA, ADP, and phosphate. Pyruvate stimulates enzymatic activity to a slight extent. Acetyl-CoA carboxylase from Cyclotella cryptica is not inhibited by cyclohexanedione or aryloxyphenoxypropionic acid herbicides as strongly as monocot acetyl-CoA carboxylases; 50% and 0% inhibition was observed in the presence of 23 micromolar clethodim and 100 micromolar haloxyfop, respectively.
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PMID:Purification and Characterization of Acetyl-CoA Carboxylase from the Diatom Cyclotella cryptica. 1666 68

Acetyl-CoA carboxylase (ACC) catalyzes the carboxylation of acetyl-CoA to form malonyl-CoA, a key metabolite in the fatty acid synthetic and oxidation pathways. The present study describes the steady-state kinetic analysis of a purified recombinant human form of the enzyme, namely ACC2, using a novel LC/MS/MS assay to directly measure malonyl-CoA formation. Four dimensional matrices, in which bicarbonate (HCO(3)(-)), ATP, acetyl-CoA, and citrate were varied, and global data fitting to appropriate steady-state equations were used to generate kinetic constants. Product inhibition studies support the notion that the enzyme proceeds through a hybrid (two-site) random Ter Ter mechanism, one that likely involves a two-step reaction at the biotin carboxylase domain. Citrate, a known activator of animal forms of ACC, activates both by increasing k(cat) and k(cat)/K(M) for ATP and acetyl-CoA.
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PMID:Characterization of recombinant human acetyl-CoA carboxylase-2 steady-state kinetics. 1923 60

Mesophilic Crenarchaeota have recently been thought to be significant contributors to nitrogen (N) and carbon (C) cycling. In this study, we examined the vertical distribution of ammonia-oxidizing Crenarchaeota at offshore site in Southern Tyrrhenian Sea. The median value of the crenachaeal cell to amoA gene ratio was close to one suggesting that virtually all deep-sea Crenarchaeota possess the capacity to oxidize ammonia. Crenarchaea-specific genes, nirK and ureC, for nitrite reductase and urease were identified and their affiliation demonstrated the presence of 'deep-sea' clades distinct from 'shallow' representatives. Measured deep-sea dark CO(2) fixation estimates were comparable to the median value of photosynthetic biomass production calculated for this area of Tyrrhenian Sea, pointing to the significance of this process in the C cycle of aphotic marine ecosystems. To elucidate the pivotal organisms in this process, we targeted known marine crenarchaeal autotrophy-related genes, coding for acetyl-CoA carboxylase (accA) and 4-hydroxybutyryl-CoA dehydratase (4-hbd). As in case of nirK and ureC, these genes are grouped with deep-sea sequences being distantly related to those retrieved from the epipelagic zone. To pair the molecular data with specific functional attributes we performed [(14)C]HCO(3) incorporation experiments followed by analyses of radiolabeled proteins using shotgun proteomics approach. More than 100 oligopeptides were attributed to 40 marine crenarchaeal-specific proteins that are involved in 10 different metabolic processes, including autotrophy. Obtained results provided a clear proof of chemolithoautotrophic physiology of bathypelagic crenarchaeota and indicated that this numerically predominant group of microorganisms facilitate a hitherto unrecognized sink for inorganic C of a global importance.
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PMID:Contribution of crenarchaeal autotrophic ammonia oxidizers to the dark primary production in Tyrrhenian deep waters (Central Mediterranean Sea). 2120 65