(1) 3-methylbutanoyl-CoA + a malonyl-[acyl-carrier protein] = a 5-methyl-3-oxohexanoyl-[acyl-carrier-protein] + CoA + CO2 [RN:R12732];
(2) 2-methylpropanoyl-CoA + a malonyl-[acyl-carrier protein] = a 4-methyl-3-oxopentanoyl-[acyl-carrier-protein] + CoA + CO2 [RN:R12733];
(3) (2S)-2-methylbutanoyl-CoA + a malonyl-[acyl-carrier protein] = a (4S)-4-methyl-3-oxohexanoyl-[acyl-carrier-protein] + CoA + CO2 [RN:R12734]
5-methyl-3-oxohexanoyl-[acyl-carrier-protein] [CPD:C22368];
CoA [CPD:C00010];
CO2 [CPD:C00011];
4-methyl-3-oxopentanoyl-[acyl-carrier-protein] [CPD:C22369];
(4S)-4-methyl-3-oxohexanoyl-[acyl-carrier-protein] [CPD:C22370]
Comment
The enzyme is responsible for initiating branched-chain fatty acid biosynthesis by the dissociated (or type II) fatty-acid biosynthesis system (FAS-II) in some bacteria, using molecules derived from degradation of the branched-chain amino acids L-leucine, L-valine, and L-isoleucine to form the starting molecules for elongation by the FAS-II system. In some organisms the enzyme is also able to use acetyl-CoA, leading to production of a mix of branched-chain and straight-chain fatty acids [3] (cf. EC 2.3.1.180, beta-ketoacyl-[acyl-carrier-protein] synthase III).
Characterization of beta-ketoacyl-acyl carrier protein synthase III from Streptomyces glaucescens and its role in initiation of fatty acid biosynthesis.
