The Enzyme Database

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Accepted name: β-ketoacyl-[acyl-carrier-protein] synthase III
Reaction: acetyl-CoA + a malonyl-[acyl-carrier protein] = an acetoacetyl-[acyl-carrier protein] + CoA + CO2
Other name(s): 3-oxoacyl:ACP synthase III; 3-ketoacyl-acyl carrier protein synthase III; KASIII; KAS III; FabH; β-ketoacyl-acyl carrier protein synthase III; β-ketoacyl-ACP synthase III; β-ketoacyl (acyl carrier protein) synthase III; acetyl-CoA:malonyl-[acyl-carrier-protein] C-acyltransferase
Systematic name: acetyl-CoA:malonyl-[acyl-carrier protein] C-acyltransferase
Comments: The enzyme is responsible for initiating straight-chain fatty acid biosynthesis by the dissociated (or type II) fatty-acid biosynthesis system that occurs in plants and bacteria. In contrast to EC, β-ketoacyl-[acyl-carrier-protein] synthase I, and EC, β-ketoacyl-[acyl-carrier-protein] synthase II, this enzyme specifically uses short-chain acyl-CoA thioesters (preferably acetyl-CoA) rather than acyl-[acp] as its substrate [1]. The enzyme can also catalyse the reaction of EC, [acyl-carrier-protein] S-acetyltransferase, but to a much lesser extent [1]. The enzymes from some organisms (e.g. the Gram-positive bacterium Streptococcus pneumoniae) can accept branched-chain acyl-CoAs in addition to acetyl-CoA [5] (cf. EC, branched-chain β-ketoacyl-[acyl-carrier-protein] synthase).
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, PDB, CAS registry number: 1048646-78-1
1.  Tsay, J.T., Oh, W., Larson, T.J., Jackowski, S. and Rock, C.O. Isolation and characterization of the β-ketoacyl-acyl carrier protein synthase III gene (fabH) from Escherichia coli K-12. J. Biol. Chem. 267 (1992) 6807–6814. [PMID: 1551888]
2.  Cronan, J.E., Jr. and Rock, C.O. 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, 1996, pp. 612–636.
3.  Han, L., Lobo, S. and Reynolds, K.A. Characterization of β-ketoacyl-acyl carrier protein synthase III from Streptomyces glaucescens and its role in initiation of fatty acid biosynthesis. J. Bacteriol. 180 (1998) 4481–4486. [DOI] [PMID: 9721286]
4.  Choi, K.H., Kremer, L., Besra, G.S. and Rock, C.O. Identification and substrate specificity of β-ketoacyl (acyl carrier protein) synthase III (mtFabH) from Mycobacterium tuberculosis. J. Biol. Chem. 275 (2000) 28201–28207. [DOI] [PMID: 10840036]
5.  Khandekar, S.S., Gentry, D.R., Van Aller, G.S., Warren, P., Xiang, H., Silverman, C., Doyle, M.L., Chambers, P.A., Konstantinidis, A.K., Brandt, M., Daines, R.A. and Lonsdale, J.T. Identification, substrate specificity, and inhibition of the Streptococcus pneumoniae β-ketoacyl-acyl carrier protein synthase III (FabH). J. Biol. Chem. 276 (2001) 30024–30030. [DOI] [PMID: 11375394]
6.  Qiu, X., Choudhry, A.E., Janson, C.A., Grooms, M., Daines, R.A., Lonsdale, J.T. and Khandekar, S.S. Crystal structure and substrate specificity of the β-ketoacyl-acyl carrier protein synthase III (FabH) from Staphylococcus aureus. Protein Sci. 14 (2005) 2087–2094. [DOI] [PMID: 15987898]
7.  Li, Y., Florova, G. and Reynolds, K.A. Alteration of the fatty acid profile of Streptomyces coelicolor by replacement of the initiation enzyme 3-ketoacyl acyl carrier protein synthase III (FabH). J. Bacteriol. 187 (2005) 3795–3799. [DOI] [PMID: 15901703]
[EC created 2006, modified 2021]

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