This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
|Superclasses:||Generation of Precursor Metabolites and Energy → Acetyl-CoA Biosynthesis|
Expected Taxonomic Range: Magnoliophyta
Acetyl-CoA is a central metabolite that plays important roles in many aspects of metabolism. In plant cells, there are at least four distinct acetyl-CoA pools in different subcellular compartments, the cytosol, the mitochondrion, the plastid, and the microbody. Each pool is used in the biosynthesis of distinct metabolites in the corresponding subcellular location. The cytosolic acetyl-CoAs are substrates for the synthesis of many secondary metabolites including flavonoids and terpenoids, and very long chain fatty acids which are themselves substrates for storage lipids and cuticle waxes. The mitochondrial acetyl-CoAs feed into the TCA cycle for the generation of energy and reducing power. The plastid acetyl-CoAs serve as precursors of de novo fatty acid biosynthesis. In the glyoxysome, acetyl-CoAs generated from the breakdown of storage lipids are converted to carbohydrates via the glyoxylate cycle and gluconeogenesis.
Research advances in the recent years have addressed questions concerning where the individual acetyl-CoA pools are made from, especially for the mitochondrial, plastid and cytosolic pools. In the mitochondrion and plastid, acetyl-CoA is derived from pyruvate by pyruvate dehydrogenase complex composed of three enzyme activities, pyruvate dehydrogenase, dihydrolipoyl acetyltransferase, and dihydrolipoyl dehydrogenase. Pyruvate is generated from glycolysis in the cytosol which then enters the mitochondrion. In the plastid, pyruvate is generated from the Calvin cycle. Plants have two forms of pyruvate dehydrogenase complex, one in the plastid and the other in the mitochondrion. The two complexes differ in many aspects of enzyme characteristics and regulations. In the cytosol, acetyl-CoA is generated from citrate, which itself is derived from the TCA cycle and exported out of the mitochondrion. The conversion of citrate to acetyl-CoA is catalyzed by citrate-ATP lyase. This enzyme activity has only been detected in plants and vertebrates.
Unification Links: AraCyc:PWY-5173
Fatland02: Fatland BL, Ke J, Anderson MD, Mentzen WI, Cui LW, Allred CC, Johnston JL, Nikolau BJ, Wurtele ES (2002). "Molecular characterization of a heteromeric ATP-citrate lyase that generates cytosolic acetyl-coenzyme A in Arabidopsis." Plant Physiol 130(2);740-56. PMID: 12376641
Mooney99: Mooney BP, Miernyk JA, Randall DD (1999). "Cloning and characterization of the dihydrolipoamide S-acetyltransferase subunit of the plastid pyruvate dehydrogenase complex (E2) from Arabidopsis." Plant Physiol 120(2);443-52. PMID: 10364395
Aoshima04: Aoshima M, Ishii M, Igarashi Y (2004). "A novel enzyme, citryl-CoA lyase, catalysing the second step of the citrate cleavage reaction in Hydrogenobacter thermophilus TK-6." Mol Microbiol 52(3);763-70. PMID: 15101982
Aoshima04a: Aoshima M, Ishii M, Igarashi Y (2004). "A novel enzyme, citryl-CoA synthetase, catalysing the first step of the citrate cleavage reaction in Hydrogenobacter thermophilus TK-6." Mol Microbiol 52(3);751-61. PMID: 15101981
Camp88: Camp, Pamela J, Miernyk, Jan A, Randall, Douglas D (1988). "Some kinetic and regulatory properties of the pea chloroplast pyruvate dehydrogenase complex." Biochimica et Biophysica Acta, 933:269-275.
Ciszak03: Ciszak EM, Korotchkina LG, Dominiak PM, Sidhu S, Patel MS (2003). "Structural basis for flip-flop action of thiamin pyrophosphate-dependent enzymes revealed by human pyruvate dehydrogenase." J Biol Chem 278(23);21240-6. PMID: 12651851
Fries03: Fries M, Jung HI, Perham RN (2003). "Reaction mechanism of the heterotetrameric (alpha2beta2) E1 component of 2-oxo acid dehydrogenase multienzyme complexes." Biochemistry 42(23);6996-7002. PMID: 12795594
Harmych02: Harmych S, Arnette R, Komuniecki R (2002). "Role of dihydrolipoyl dehydrogenase (E3) and a novel E3-binding protein in the NADH sensitivity of the pyruvate dehydrogenase complex from anaerobic mitochondria of the parasitic nematode, Ascaris suum." Mol Biochem Parasitol 125(1-2);135-46. PMID: 12467981
Head05: Head RA, Brown RM, Zolkipli Z, Shahdadpuri R, King MD, Clayton PT, Brown GK (2005). "Clinical and genetic spectrum of pyruvate dehydrogenase deficiency: dihydrolipoamide acetyltransferase (E2) deficiency." Ann Neurol 58(2);234-41. PMID: 16049940
Himmelreich96: Himmelreich R, Hilbert H, Plagens H, Pirkl E, Li BC, Herrmann R (1996). "Complete sequence analysis of the genome of the bacterium Mycoplasma pneumoniae." Nucleic Acids Res 1996;24(22);4420-49. PMID: 8948633
Howard98: Howard MJ, Fuller C, Broadhurst RW, Perham RN, Tang JG, Quinn J, Diamond AG, Yeaman SJ (1998). "Three-dimensional structure of the major autoantigen in primary biliary cirrhosis." Gastroenterology 115(1);139-46. PMID: 9649469
Hugler05: Hugler M, Wirsen CO, Fuchs G, Taylor CD, Sievert SM (2005). "Evidence for autotrophic CO2 fixation via the reductive tricarboxylic acid cycle by members of the epsilon subdivision of proteobacteria." J Bacteriol 187(9);3020-7. PMID: 15838028
Kanao01: Kanao T, Fukui T, Atomi H, Imanaka T (2001). "ATP-citrate lyase from the green sulfur bacterium Chlorobium limicola is a heteromeric enzyme composed of two distinct gene products." Eur J Biochem 268(6);1670-8. PMID: 11248686
Manolukas88: Manolukas JT, Barile MF, Chandler DK, Pollack JD (1988). "Presence of anaplerotic reactions and transamination, and the absence of the tricarboxylic acid cycle in mollicutes." J Gen Microbiol 1988;134 ( Pt 3);791-800. PMID: 3141576
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