If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Synonyms: palmitic acid biosynthesis, de novo lipogenesis
|Superclasses:||Biosynthesis → Fatty Acid and Lipid Biosynthesis → Fatty Acid Biosynthesis → Palmitate Biosynthesis|
Expected Taxonomic Range: Opisthokonta
Fatty acids are key building blocks for the phospholipid components of cell membranes and are determinants of intracellular communication, in the form of lipid second messengers [Prieschl00], and fatty acyl moieties of proteins that modify their location and function [Resh99].
There are two basic types of fatty acid (FAS) biosynthesis mechanisms, named type I and type II. The type I system is found in mammals and lower eukaryotes. The mammalian system consists of a single gene product that contains all of the reaction centers required to produce a fatty acid (see fatty acid synthase from Homo sapiens), while the system of lower eukaryotes (such as yeast) consists of two genes, whose polypeptide products combine to form a multifunctional complex (see fatty acid synthase from Saccharomyces cerevisiae).
Type II systems are found in bacteria, plants [White05], parasites of the Apicomplexa phylum [Ferguson07] and mitochondria [Zhang03e, 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].
A major difference between the two pathways is that the type I systems accept malonyl-CoA as the source of two-carbon units, while the type II systems accept a malonyl-[acp]. The pathway catalyzed by the type II systems is available at palmitate biosynthesis II (bacteria and plants).
About This Pathway
Mammalian fatty acid synthase enzymes are homodimers whose gigantic subunits (about 240 kDa) are encoded by a single gene [Guy78]. Each subunit is multifunctional protein, whose main function is to catalyze the synthesis of palmitate from acetyl-CoA and malonyl-CoA in the presence of NADPH. The two subunits are arranged in a head to tail fashion, and each subunit contains, in addition to an acyl-carrier-protein (acp) domain, additional domains that catalyze 7 different catalytic activities.
The complex catalyzes seven successive cycles, and the final product is palmitoyl-CoA. Although small amounts of stearate are sometimes formed through the actions of FAS, the process generally stops at 16 carbons, and palmitate is released from the ACP moiety [Sampath05].
A general description of the reactions catalyzed by the mammalian fatty acid synthase complex is provided by EC reaction 22.214.171.124:
The sum of reactions catalyzed by the yeast enzyme is described by EC reaction 126.96.36.199:
Palmitate is one of the most common saturated fatty acids found in animals and plants. It was discovered by Edmond Fremy in 1840 in saponified palm oil, of which it is a major component, hence its name.
Insulin, 3,5,3'-triiodo-L-thyronine, glucocorticoids, and D-glucose induce de novo lipogenesis, while C20 PUFAs (polyunsaturated fatty acids), glucagon, and (R)-adrenaline suppress it [Hillgartner95].
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Guy78: Guy P, Law S, Hardie G (1978). "Mammalian fatty acid synthetase: evidence for subunit identity and specific removal of the thioesterase component using elastase digestion." FEBS Lett 94(1);33-7. PMID: 700134
Hillgartner95: Hillgartner FB, Salati LM, Goodridge AG (1995). "Physiological and molecular mechanisms involved in nutritional regulation of fatty acid synthesis." Physiol Rev 75(1);47-76. PMID: 7831398
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
Zhang03e: 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
Airenne03: Airenne TT, Torkko JM, Van den plas S, Sormunen RT, Kastaniotis AJ, Wierenga RK, Hiltunen JK (2003). "Structure-function analysis of enoyl thioester reductase involved in mitochondrial maintenance." J Mol Biol 327(1);47-59. PMID: 12614607
Brink02: Brink J, Ludtke SJ, Yang CY, Gu ZW, Wakil SJ, Chiu W (2002). "Quaternary structure of human fatty acid synthase by electron cryomicroscopy." Proc Natl Acad Sci U S A 99(1);138-43. PMID: 11756679
Chi09: Chi A, Rhee S (2009). "The functional annotation of Arabidopsis protein sequences was performed by BLAST queries against a reference set of experimentally verified enzymes. For each Arabidopsis sequence, the enzymatic activity of the top BLAST hit (or hits if they had equivalent E-values) was assigned to the protein if its E-value fell below a specific E-value threshold established for the corresponding enzymatic activity. Note: The annotation thresholds were established by doing a self BLAST of the reference enzyme dataset. For each enzymatic activity represented by multiple proteins, the mean E-value of all the correct hits generated by the self BLAST was selected as the cut-off. All of these means were averaged and used as the cut-off for assigning annotations for any enzymatic activities that were represented by a single protein in the reference dataset."
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Jayakumar94: Jayakumar A, Chirala SS, Chinault AC, Baldini A, Abu-Elheiga L, Wakil SJ (1994). "Isolation and chromosomal mapping of genomic clones encoding the human fatty acid synthase gene." Genomics 23(2);420-4. PMID: 7835891
Jayakumar95: Jayakumar A, Tai MH, Huang WY, al-Feel W, Hsu M, Abu-Elheiga L, Chirala SS, Wakil SJ (1995). "Human fatty acid synthase: properties and molecular cloning." Proc Natl Acad Sci U S A 92(19);8695-9. PMID: 7567999
Joseph02: Joseph SB, Laffitte BA, Patel PH, Watson MA, Matsukuma KE, Walczak R, Collins JL, Osborne TF, Tontonoz P (2002). "Direct and indirect mechanisms for regulation of fatty acid synthase gene expression by liver X receptors." J Biol Chem 277(13);11019-25. PMID: 11790787
Kastaniotis04: Kastaniotis AJ, Autio KJ, Sormunen RT, Hiltunen JK (2004). "Htd2p/Yhr067p is a yeast 3-hydroxyacyl-ACP dehydratase essential for mitochondrial function and morphology." Mol Microbiol 53(5);1407-21. PMID: 15387819
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