Updated BioCyc iOS App now
available in iTunes store
Updated BioCyc iOS App now
available in iTunes store
Updated BioCyc iOS App now
available in iTunes store
Updated BioCyc iOS App now
available in iTunes store
Updated BioCyc iOS App now
available in iTunes store

MetaCyc Reaction:

Superclasses: Reactions Classified By Conversion TypeSimple ReactionsChemical ReactionsProtein-Modification Reactions
Reactions Classified By SubstrateMacromolecule ReactionsProtein-ReactionsProtein-Modification Reactions

EC Number:,,

Enzymes and Genes:

Arabidopsis thaliana col: 3-oxoacyl-[acyl-carrier-protein] synthase I, chloroplasticInferred from experiment: KASI
Escherichia coli K-12 substr. MG1655: KASIInferred from experiment: fabB
KASIIInferred from experiment: fabF
Homo sapiens: fatty acid synthaseInferred from experiment: FASN
Saccharomyces cerevisiae: fatty acid synthase, α subunit: FAS2

In Pathway: fatty acid elongation -- saturated

Note that this reaction equation differs from the official Enzyme Commission reaction equation for this EC number, which can be found here .

The direction shown, i.e. which substrates are on the left and right sides, is in accordance with the Enzyme Commission system.

Most BioCyc compounds have been protonated to a reference pH value of 7.3. Please see the PGDB Concepts Guide for more information.

Mass balance status: Marked as unbalanced.

Enzyme Commission Primary Name for β-ketoacyl-[acyl-carrier-protein] synthase I

Enzyme Commission Synonyms for β-ketoacyl-ACP synthase I, β-ketoacyl synthetase, β-ketoacyl-ACP synthetase, β-ketoacyl-acyl carrier protein synthetase, β-ketoacyl-[acyl carrier protein] synthase, β-ketoacylsynthase, condensing enzyme, 3-ketoacyl-acyl carrier protein synthase, fatty acid condensing enzyme, acyl-malonyl(acyl-carrier-protein)-condensing enzyme, acyl-malonyl acyl carrier protein-condensing enzyme, β-ketoacyl acyl carrier protein synthase, 3-oxoacyl-[acyl-carrier-protein] synthase, 3-oxoacyl:ACP synthase I, KASI, KAS I, FabF1, FabB, acyl-[acyl-carrier-protein]:malonyl-[acyl-carrier-protein] C-acyltransferase (decarboxylating)

Enzyme Commission Primary Name for fatty-acid synthase

Enzyme Commission Synonyms for FASN (gene name)

Enzyme Commission Primary Name for fatty-acyl-CoA synthase

Enzyme Commission Synonyms for yeast fatty acid synthase, FAS1 (gene name), FAS2 (gene name)

Standard Gibbs Free Energy (ΔrG in kcal/mol): -10.102905Inferred by computational analysis [Latendresse13]

Enzyme Commission Summary for
This enzyme is responsible for the chain-elongation step of dissociated (type II) fatty-acid biosynthesis, i.e. the addition of two C atoms to the fatty-acid chain. Escherichia coli mutants that lack this enzyme are deficient in unsaturated fatty acids. The enzyme can use fatty acyl thioesters of ACP (C2 to C16) as substrates, as well as fatty acyl thioesters of Co-A (C4 to C16) [DAgnolo75]. The substrate specificity is very similar to that of EC, β-ketoacyl-ACP synthase II, with the exception that the latter enzyme is far more active with palmitoleoyl-ACP (C16Δ9) as substrate, allowing the organism to regulate its fatty-acid composition with changes in temperature [DAgnolo75, Garwin80].

Enzyme Commission Summary for
The animal enzyme is a multi-functional protein catalysing the reactions of EC, [acyl-carrier-protein] S-acetyltransferase, EC, [acyl-carrier-protein] S-malonyltransferase, EC, β-ketoacyl-[acyl-carrier-protein] synthase I, EC, 3-oxoacyl-[acyl-carrier-protein] reductase, EC, 3-hydroxyacyl-[acyl-carrier-protein] dehydratase, EC, enoyl-[acyl-carrier-protein] reductase (NADPH, Re-specific) and EC, oleoyl-[acyl-carrier-protein] hydrolase. cf. EC, fatty-acyl-CoA synthase.

Enzyme Commission Summary for
The enzyme from yeasts ( Ascomycota and Basidiomycota) is a multi-functional protein complex composed of two subunits. One subunit catalyses the reactions EC, 3-oxoacyl-[acyl-carrier-protein] reductase and EC, β-ketoacyl-[acyl-carrier-protein] synthase I, while the other subunit catalyses the reactions of EC, [acyl-carrier-protein] S-acetyltransferase, EC, [acyl-carrier-protein] S-malonyltransferase, EC, 3-hydroxyacyl-[acyl-carrier-protein] dehydratase, EC, enoyl-[acyl-carrier-protein] reductase (NADPH, Si-specific) and EC, (R)-3-hydroxyacid-ester dehydrogenase. The enzyme differs from the animal enzyme ( EC in that the enoyl reductase domain requires FMN as a cofactor, and the ultimate product is an acyl-CoA (usually palmitoyl-CoA) instead of a free fatty acid.

Citations: [Prescott72, Toomey66a, Wang04, Cronan96, Alberts69, Stoops79, Wakil83, Schweizer73, Tehlivets07]

Gene-Reaction Schematic

Gene-Reaction Schematic

Relationship Links: BRENDA:EC:, BRENDA:EC:, BRENDA:EC:, ENZYME:EC:, ENZYME:EC:, ENZYME:EC:, IUBMB-ExplorEnz:EC:, IUBMB-ExplorEnz:EC:, IUBMB-ExplorEnz:EC:, UniProt:RELATED-TO:O23738, UniProt:RELATED-TO:O25284, UniProt:RELATED-TO:O34340, UniProt:RELATED-TO:O54440, UniProt:RELATED-TO:O64485, UniProt:RELATED-TO:O65677, UniProt:RELATED-TO:O67612, UniProt:RELATED-TO:P0A6R0, UniProt:RELATED-TO:P0A953, UniProt:RELATED-TO:P0AAI5, UniProt:RELATED-TO:P12276, UniProt:RELATED-TO:P12785, UniProt:RELATED-TO:P20582, UniProt:RELATED-TO:P23902, UniProt:RELATED-TO:P31176, UniProt:RELATED-TO:P41175, UniProt:RELATED-TO:P43710, UniProt:RELATED-TO:P43711, UniProt:RELATED-TO:P49327, UniProt:RELATED-TO:P55338, UniProt:RELATED-TO:P73283, UniProt:RELATED-TO:Q9HYR2, UniProt:RELATED-TO:Q9JT63, UniProt:RELATED-TO:Q9JW56, UniProt:RELATED-TO:Q9JX65, UniProt:RELATED-TO:Q9PI63, UniProt:RELATED-TO:Q9PMZ6, UniProt:RELATED-TO:Q9RA31, UniProt:RELATED-TO:Q06097, UniProt:RELATED-TO:Q07510, UniProt:RELATED-TO:Q39310, UniProt:RELATED-TO:Q40027, UniProt:RELATED-TO:Q40028, UniProt:RELATED-TO:Q41134, UniProt:RELATED-TO:Q41135, UniProt:RELATED-TO:Q54208


Alberts69: Alberts AW, Majerus PW, Vagelos PR (1969). "Acetyl-CoA acyl carrier protein transacylase." Methods Enzymol. 14 5053.

Cronan96: Cronan JE Jr., Rock CO (1996). "Biosynthesis of membrane lipids." In: Neidhardt, F.C. (Ed.), Escherichia coli and Salmonella: Cellular and Molecular Biology, 2nd edn, vol. 1, ASM Press, Washington, DC, pp. 612-636.

DAgnolo75: D'Agnolo G, Rosenfeld IS, Vagelos PR (1975). "Multiple forms of beta-ketoacyl-acyl carrier protein synthetase in Escherichia coli." J Biol Chem 250(14);5289-94. PMID: 237914

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

Latendresse13: Latendresse M. (2013). "Computing Gibbs Free Energy of Compounds and Reactions in MetaCyc."

Prescott72: Prescott DJ, Vagelos PR (1972). "Acyl carrier protein." Adv Enzymol Relat Areas Mol Biol 36;269-311. PMID: 4561013

Schweizer73: Schweizer E, Kniep B, Castorph H, Holzner U (1973). "Pantetheine-free mutants of the yeast fatty-acid-synthetase complex." Eur J Biochem 39(2);353-62. PMID: 4590449

Stoops79: Stoops JK, Ross P, Arslanian MJ, Aune KC, Wakil SJ, Oliver RM (1979). "Physicochemical studies of the rat liver and adipose fatty acid synthetases." J Biol Chem 254(15);7418-26. PMID: 457689

Tehlivets07: Tehlivets O, Scheuringer K, Kohlwein SD (2007). "Fatty acid synthesis and elongation in yeast." Biochim Biophys Acta 1771(3);255-70. PMID: 16950653

Toomey66a: Toomey RE, Wakil SJ (1966). "Studies on the mechanism of fatty acid synthesis. XVI. Preparation and general properties of acyl-malonyl acyl carrier protein-condensing enzyme from Escherichia coli." J Biol Chem 241(5);1159-65. PMID: 5327099

Wakil83: Wakil SJ, Stoops JK, Joshi VC (1983). "Fatty acid synthesis and its regulation." Annu Rev Biochem 52;537-79. PMID: 6137188

Wang04: Wang H, Cronan JE (2004). "Functional replacement of the FabA and FabB proteins of Escherichia coli fatty acid synthesis by Enterococcus faecalis FabZ and FabF homologues." J Biol Chem 279(33);34489-95. PMID: 15194690

Report Errors or Provide Feedback
Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
Page generated by Pathway Tools version 19.5 (software by SRI International) on Fri Apr 29, 2016, biocyc13.