BETA-KETOACYL-ACYL CARRIER PROTEIN SYNTHASES IN THE REGULATION OF FATTY-ACID SYNTHASE ACTIVITY IN HIGHER-PLANTS - AN OVERVIEW

The role of beta-ketoacyl-ACP synthases (condensing enzymes, KAS) in t he regulation of the biosynthesis of medium-chain fatty acids in Cuphe a lanceolata seed (86.5% decanoic acid in oil) was investigated. KAS I II catalyzes the first condensing step of fatty acid synthase (FAS) re action between acetyl-CoA and malonyl-ACP. This condensing reaction wa s highly sensitive to inhibition by decanoyl-ACP, as determined using FAS preparations from C. lanceolata seeds. These data provide strong e vidences that KAS III is a target for feedback regulation of fatty aci d biosynthesis. Studies on the elongation of octanoyl-and hexadecanoyl -ACP by KAS I and KAS II, respectively, showed that the accumulation o f beta-ketoacyl-ACP, the direct product of condensing reaction, result s in decarboxylation of malonyl-ACP to acetyl-ACP. The data demonstrat e that condensing enzymes can modulate the levels of malonyl-ACP insid e the plastids during the fatty acid biosynthesis.