Note: a dashed line (without arrowheads) between two compound names is meant to imply that the two names are just different instantiations of the same compound -- i.e. one may be a specific name and the other a general name, or they may both represent the same compound in different stages of a polymerization-type pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Locations of Mapped Genes:
|Superclasses:||Biosynthesis → Fatty Acids and Lipids Biosynthesis → Fatty Acid Biosynthesis|
This pathway shows the reactions that constitute one turn of a cycle that lengthens the chain of an acyl-ACP molecule by two carbons. The pathway is fed acetoacetyl-ACP (see Pathway superpathway of fatty acid biosynthesis initiation (E. coli)) which is a substrate of the second reaction shown here. The products of multiple turns of this cycle that are drawn off to become components of fatty acid-containing compounds such as phospholipids, lipid A, and lipoproteins are the saturated fatty acids , lauric (dodecanoic), myristic (tetradecanoic), palmitic (hexadecanoic), and stearic (octadecanoic) acids. E. coli also contains unsaturated fatty acids. These are formed by a pathway (see cis-dodecenoyl biosynthesis) that branches at the level of the 10-carbon intermediate. [Cronan03] [Magnuson93]. The final step of the cycle, the reductase, once thought to be catalyzed by two enzymes, has been shown to be catalyzed by a single enzyme, FabI, that can use either NADH or NADPH as a cofactor. However, the activity with NADH was over 17-fold higher than with NADPH [Bergler96], thus the designation of the E. coli enzyme as EC 126.96.36.199.
Of the four reactions involved in a cycle of fatty-acid elongation, two are catalyzed by more that one enzyme. These function preferentially on substrates of different chain length. They also act differentially on saturated and unsaturated substrates [Heath96]. The first reaction in the sequence, the condensation reaction, is catalyzed by three enzymes, FabB, FabF, and FabH. FabH initiates fatty-acid synthesis: it uses only acetyl-ACP as a substrate (see Pathway superpathway of fatty acid biosynthesis initiation (E. coli)) [Lai03]. Only FabB catalyzes one step in the synthesis of unsaturated fatty acids [Campbell01] The activity of FabF and hence the fraction of fatty acids that are unsaturated in modultated by temperature. The distribution of the flow of synthesis that proceeds to saturated vs. unsaturated fatty acids is determined by the activities of FabA and FabZ [Heath96].
Superpathways: superpathway of fatty acid biosynthesis I (E. coli)
Bergler96: Bergler H, Fuchsbichler S, Hogenauer G, Turnowsky F (1996). "The enoyl-[acyl-carrier-protein] reductase (FabI) of Escherichia coli, which catalyzes a key regulatory step in fatty acid biosynthesis, accepts NADH and NADPH as cofactors and is inhibited by palmitoyl-CoA." Eur J Biochem 242(3);689-94. PMID: 9022698
Heath96: Heath RJ, Rock CO (1996). "Roles of the FabA and FabZ beta-hydroxyacyl-acyl carrier protein dehydratases in Escherichia coli fatty acid biosynthesis." J Biol Chem 1996;271(44);27795-801. PMID: 8910376
Annand93: Annand RR, Kozlowski JF, Davisson V J, Schwab JM (1993). "Mechanism-based inactivation of Escherichia coli .beta.-hydroxydecanoyl thiol ester dehydrase: assignment of the imidazole nitrogen-15 NMR resonances and determination of the structure of the alkylated histidine." Journal of the American Chemical Society 115(3);1088-1094.
Baldock96: Baldock C, Rafferty JB, Sedelnikova SE, Baker PJ, Stuitje AR, Slabas AR, Hawkes TR, Rice DW (1996). "A mechanism of drug action revealed by structural studies of enoyl reductase." Science 274(5295);2107-10. PMID: 8953047
Bergler94: Bergler H, Wallner P, Ebeling A, Leitinger B, Fuchsbichler S, Aschauer H, Kollenz G, Hogenauer G, Turnowsky F (1994). "Protein EnvM is the NADH-dependent enoyl-ACP reductase (FabI) of Escherichia coli." J Biol Chem 1994;269(8);5493-6. PMID: 8119879
Butland05: Butland G, Peregrin-Alvarez JM, Li J, Yang W, Yang X, Canadien V, Starostine A, Richards D, Beattie B, Krogan N, Davey M, Parkinson J, Greenblatt J, Emili A (2005). "Interaction network containing conserved and essential protein complexes in Escherichia coli." Nature 433(7025);531-7. PMID: 15690043
Cao10: Cao Y, Yang J, Xian M, Xu X, Liu W (2010). "Increasing unsaturated fatty acid contents in Escherichia coli by coexpression of three different genes." Appl Microbiol Biotechnol 87(1);271-80. PMID: 20135119
Clark83: Clark DP, DeMendoza D, Polacco ML, Cronan JE (1983). "Beta-hydroxydecanoyl thio ester dehydrase does not catalyze a rate-limiting step in Escherichia coli unsaturated fatty acid synthesis." Biochemistry 1983;22(25);5897-902. PMID: 6362720
Cronan88: Cronan JE, Li WB, Coleman R, Narasimhan M, de Mendoza D, Schwab JM (1988). "Derived amino acid sequence and identification of active site residues of Escherichia coli beta-hydroxydecanoyl thioester dehydrase." J Biol Chem 1988;263(10);4641-6. PMID: 2832401
DiazMejia09: Diaz-Mejia JJ, Babu M, Emili A (2009). "Computational and experimental approaches to chart the Escherichia coli cell-envelope-associated proteome and interactome." FEMS Microbiol Rev 33(1);66-97. PMID: 19054114
Edwards97: Edwards P, Nelsen JS, Metz JG, Dehesh K (1997). "Cloning of the fabF gene in an expression vector and in vitro characterization of recombinant fabF and fabB encoded enzymes from Escherichia coli." FEBS Lett 402(1);62-6. PMID: 9013860
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