If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Locations of Mapped Genes:
Synonyms: palmitic acid biosynthesis, de novo lipogenesis
|Superclasses:||Biosynthesis → Fatty Acid and Lipid Biosynthesis → Fatty Acid Biosynthesis → Palmitate Biosynthesis|
Fatty acids are key building blocks for the phospholipid components of cell membranes. Palmitate is one of the most common saturated fatty acids found in microorganisms, plants and animals. It was discovered by Edmond Fremy in 1840 in saponified palm oil, of which it is a major component, and hence its name.
Palmitate is synthesized by stepwise condensation of C2 units to a growing acyl chain. Each elongation cycle results in the addition of two carbons to the acyl chain, and consists of four separate reactions. The first step is the condensation of a C2 unit with the nascent [acyl carrier protein]-bound acyl (acyl-[acp]) forming a a 3-oxoacyl-[acp] and CO2. This step is followed by reduction to a (3R)-3-hydroxyacyl-[acyl-carrier protein], dehydration to a trans-2-enoyl-[acyl-carrier protein], and a final reduction to form the elongated fatty acyl-[acp]. This chain of event repeats itself several times, until the final product, a palmitoyl-[acp], is formed.
There are two basic types of fatty acid biosynthesis systems, named type I and type II. The type I system is found in animals and lower eukaryotes (see pathway palmitate biosynthesis I (animals and fungi)). The mammalian system consists of a single gene product that contains all of the reaction centers required to produce a fatty acid, while the system of lower eukaryotes (such as yeast) consists of two genes, whose polypeptide products combine to form a multifunctional complex.
The type II systems are found in bacteria and plants [White05], parasites of the Apicomplexa phylum [Ferguson07], and mitochondria [Zhang03c, Miinalainen03]. The reactions in these systems are catalyzed by a series of individual soluble proteins that are each encoded by a discrete gene, and the pathway intermediates are transferred between the enzymes as thioesters of a holo-[acyl-carrier protein].
Unlike the type I system that accepts malonyl-CoA as the source of the two-carbon units, the type II systems accept only a malonyl-[acp]. In E. coli the final product of this pathway is a palmitoyl-[acp]. In some bacteria and plants, but not E. coli, the acyl moiety is released from the [acyl carrier protein] by an acyl-[acyl-carrier-protein] hydrolase (EC 18.104.22.168 or EC 22.214.171.124) [Jeon11, Pollard91].
About This Pathway
This pathway is an instance of the generalized fatty acid elongation pathway depicted in fatty acid elongation -- saturated. It shows the elongation of an acetoacetyl-[acp] produced by the fatty acid biosynthesis initiation reactions (shown in superpathway of fatty acid biosynthesis initiation (E. coli)) to produce a palmitoyl-[acp].
As noted above, the final product of the E. coli pathway is a palmitoyl-[acp]. E. coli lacks an acyl-[acyl-carrier-protein] hydrolase (EC 126.96.36.199) that releases palmitate from a palmitoyl-[acp]. Instead, the acyl chain of a palmitoyl-[acp] is transferred into membrane phospholipids by a sn-glycerol 3-phosphate acyltransferase system (see pathway CDP-diacylglycerol biosynthesis II).
Ferguson07: Ferguson DJ, Campbell SA, Henriquez FL, Phan L, Mui E, Richards TA, Muench SP, Allary M, Lu JZ, Prigge ST, Tomley F, Shirley MW, Rice DW, McLeod R, Roberts CW (2007). "Enzymes of type II fatty acid synthesis and apicoplast differentiation and division in Eimeria tenella." Int J Parasitol 37(1);33-51. PMID: 17112527
Jeon11: Jeon E, Lee S, Won JI, Han SO, Kim J, Lee J (2011). "Development of Escherichia coli MG1655 strains to produce long chain fatty acids by engineering fatty acid synthesis (FAS) metabolism." Enzyme Microb Technol 49(1);44-51. PMID: 22112270
Miinalainen03: Miinalainen IJ, Chen ZJ, Torkko JM, Pirila PL, Sormunen RT, Bergmann U, Qin YM, Hiltunen JK (2003). "Characterization of 2-enoyl thioester reductase from mammals. An ortholog of YBR026p/MRF1'p of the yeast mitochondrial fatty acid synthesis type II." J Biol Chem 278(22);20154-61. PMID: 12654921
Pollard91: Pollard MR, Anderson L, Fan C, Hawkins DJ, Davies HM (1991). "A specific acyl-ACP thioesterase implicated in medium-chain fatty acid production in immature cotyledons of Umbellularia californica." Arch Biochem Biophys 284(2);306-12. PMID: 1989513
Zhang03c: Zhang L, Joshi AK, Smith S (2003). "Cloning, expression, characterization, and interaction of two components of a human mitochondrial fatty acid synthase. Malonyltransferase and acyl carrier protein." J Biol Chem 278(41);40067-74. PMID: 12882974
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
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
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
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
Escaich11: Escaich S, Prouvensier L, Saccomani M, Durant L, Oxoby M, Gerusz V, Moreau F, Vongsouthi V, Maher K, Morrissey I, Soulama-Mouze C (2011). "The MUT056399 inhibitor of FabI is a new antistaphylococcal compound." Antimicrob Agents Chemother 55(10);4692-7. PMID: 21825292
Feng09: Feng Y, Cronan JE (2009). "Escherichia coli unsaturated fatty acid synthesis: complex transcription of the fabA gene and in vivo identification of the essential reaction catalyzed by FabB." J Biol Chem 284(43);29526-35. PMID: 19679654
Garwin80: Garwin JL, Klages AL, Cronan JE (1980). "Structural, enzymatic, and genetic studies of beta-ketoacyl-acyl carrier protein synthases I and II of Escherichia coli." J Biol Chem 1980;255(24);11949-56. PMID: 7002930
Goh09: Goh S, Boberek JM, Nakashima N, Stach J, Good L (2009). "Concurrent growth rate and transcript analyses reveal essential gene stringency in Escherichia coli." PLoS One 4(6);e6061. PMID: 19557168
Heath95: Heath RJ, Rock CO (1995). "Enoyl-acyl carrier protein reductase (fabI) plays a determinant role in completing cycles of fatty acid elongation in Escherichia coli." J Biol Chem 270(44);26538-42. PMID: 7592873
Heath96a: 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
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