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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)

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

Two acyl-CoA carboxylases from Streptomyces coelicolor have been successfully reconstituted from their purified components. Both complexes shared the same biotinylated alpha subunit, AccA2. The beta and the epsilon subunits were specific from each of the complexes; thus, for the propionyl-CoA carboxylase complex the beta and epsilon components are PccB and PccE, whereas for the acetyl-CoA carboxylase complex the components are AccB and AccE. The two complexes showed very low activity in the absence of the corresponding epsilon subunits; addition of PccE or AccE dramatically increased the specific activity of the enzymes. The kinetic properties of the two acyl-CoA carboxylases showed a clear difference in their substrate specificity. The acetyl-CoA carboxylase was able to carboxylate acetyl-, propionyl-, or butyryl-CoA with approximately the same specificity. The propionyl-CoA carboxylase could not recognize acetyl-CoA as a substrate, whereas the specificity constant for propionyl-CoA was 2-fold higher than for butyryl-CoA. For both enzymes the epsilon subunits were found to specifically interact with their carboxyltransferase component forming a beta-epsilon subcomplex; this appears to facilitate the further interaction of these subunits with the alpha component. The epsilon subunit has been found genetically linked to several carboxyltransferases of different Streptomyces species; we propose that this subunit reflects a distinctive characteristic of a new group of acyl-CoA carboxylases.
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PMID:Kinetic and structural analysis of a new group of Acyl-CoA carboxylases found in Streptomyces coelicolor A3(2). 1204 95

Biotin has a profound effect on the metabolism of rhizobia. It is reported here that the activities of the biotin-dependent enzymes acetyl-coenzyme A carboxylase (ACC; EC 6.4.1.2) and propionyl-coenzyme A carboxylase (PCC; EC 6.4.1.3) are present in all species of the five genera comprising the Rhizobiaceae which were examined. Evidence is presented that the ACC and PCC activities detectable in Rhizobium etli extracts are catalysed by a single acyl-coenzyme A carboxylase. The enzyme from R. etli strain 12-53 was purified 478-fold and displayed its highest activity with propionyl-CoA as substrate, with apparent K(m) and V(max) values of 0.064 mM and 2885 nmol min(-1) (mg protein)(-1), respectively. The enzyme carboxylated acetyl-CoA and butyryl-CoA with apparent K(m) values of 0.392 and 0.144 mM, respectively, and V(max) values of 423 and 268 nmol min(-1) (mg protein)(-1), respectively. K(+), or Cs(+) markedly activated the enzyme, which was essentially inactive in their absence. Electrophoretic analysis indicated that the acyl-CoA carboxylase was composed of a 74 kDa biotin-containing alpha subunit and a 45 kDa biotin-free beta subunit, and gel chromatography indicated a total molecular mass of 620 000 Da. The strong kinetic preference of the enzyme for propionyl-CoA is consistent with its participation in an anaplerotic pathway utilizing this substrate.
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PMID:Biochemical characterization of a Rhizobium etli monovalent cation-stimulated acyl-coenzyme A carboxylase with a high substrate specificity constant for propionyl-coenzyme A. 1476 18

The first committed step of fatty acid and polyketides biosynthesis, the biotin-dependent carboxylation of an acyl-CoA, is catalyzed by acyl-CoA carboxylases (ACCases) such as acetyl-CoA carboxylase (ACC) and propionyl-CoA carboxylase (PCC). ACC and PCC in Streptomyces coelicolor are homologue multisubunit complexes that can carboxylate different short chain acyl-CoAs. While ACC is able to carboxylate acetyl-, propionyl-, or butyryl-CoA with approximately the same specificity, PCC only recognizes propionyl- and butyryl-CoA as substrates. How ACC and PCC have such different specificities toward these substrates is only partially understood. To further understand the molecular basis of how the active site residues can modulate the substrate recognition, we mutated D422, N80, R456, and R457 of PccB, the catalytic beta subunit of PCC. The crystal structures of six PccB mutants and the wild type crystal structure were compared systematically to establish the sequence-structure-function relationship that correlates the observed substrate specificity toward acetyl-, propionyl-, and butyryl-CoA with active site geometry. The experimental data confirmed that D422 is a key determinant of substrate specificity, influencing not only the active site properties but further altering protein stability and causing long-range conformational changes. Mutations of N80, R456, and R457 lead to variations in the quaternary structure of the beta subunit and to a concomitant loss of enzyme activity, indicating the importance of these residues in maintaining the active protein conformation as well as a critical role in substrate binding.
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PMID:Crystal structures and mutational analyses of acyl-CoA carboxylase beta subunit of Streptomyces coelicolor. 2069 Jun

A limited number of enzymes are known that play a role analogous to DNA proofreading by eliminating non-classical metabolites formed by side activities of enzymes of intermediary metabolism. Because few such "metabolite proofreading enzymes" are known, our purpose was to search for an enzyme able to degrade ethylmalonyl-CoA, a potentially toxic metabolite formed at a low rate from butyryl-CoA by acetyl-CoA carboxylase and propionyl-CoA carboxylase, two major enzymes of lipid metabolism. We show that mammalian tissues contain a previously unknown enzyme that decarboxylates ethylmalonyl-CoA and, at lower rates, methylmalonyl-CoA but that does not act on malonyl-CoA. Ethylmalonyl-CoA decarboxylase is particularly abundant in brown adipose tissue, liver, and kidney in mice, and is essentially cytosolic. Because Escherichia coli methylmalonyl-CoA decarboxylase belongs to the family of enoyl-CoA hydratase (ECH), we searched mammalian databases for proteins of uncharacterized function belonging to the ECH family. Combining this database search approach with sequencing data obtained on a partially purified enzyme preparation, we identified ethylmalonyl-CoA decarboxylase as ECHDC1. We confirmed this identification by showing that recombinant mouse ECHDC1 has a substantial ethylmalonyl-CoA decarboxylase activity and a lower methylmalonyl-CoA decarboxylase activity but no malonyl-CoA decarboxylase or enoyl-CoA hydratase activity. Furthermore, ECHDC1-specific siRNAs decreased the ethylmalonyl-CoA decarboxylase activity in human cells and increased the formation of ethylmalonate, most particularly in cells incubated with butyrate. These findings indicate that ethylmalonyl-CoA decarboxylase may correct a side activity of acetyl-CoA carboxylase and suggest that its mutation may be involved in the development of certain forms of ethylmalonic aciduria.
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PMID:Ethylmalonyl-CoA decarboxylase, a new enzyme involved in metabolite proofreading. 2201 88