betaketoacylACP

Beta-ketoacyl-ACP refers to a beta-ketoacyl thioester of an acyl carrier protein (ACP). It is a key transient intermediate in the type II fatty acid synthase (FAS II) pathway, found in many bacteria and plant plastids, and it participates in iterative chain elongation to produce long-chain fatty acids for membranes.

In bacteria, the first condensation that generates a beta-ketoacyl-ACP is catalyzed by FabH (beta-ketoacyl-ACP synthase III). FabH condenses acetyl-ACP with malonyl-ACP to form beta-ketoacyl-ACP, typically a four-carbon molecule. Subsequent elongation is performed by FabB and FabF (KAS I and KAS II), which condense malonyl-ACP with the growing acyl-ACP to extend the beta-ketoacyl-ACP by two carbons per cycle.

The beta-ketoacyl-ACP intermediate is then processed by a sequence of enzymes that convert it to a longer, fully reduced acyl-ACP. Beta-ketoacyl-ACP reductase (FabG) reduces it to beta-hydroxyacyl-ACP, beta-hydroxyacyl-ACP dehydratase (FabA or FabZ) dehydrates it to enoyl-ACP, and enoyl-ACP reductase (FabI) reduces it to a longer, saturated acyl-ACP. This cycle repeats until the fatty acid reaches the desired length, after which the acyl-ACP is used for phospholipid synthesis or other lipids.

Beta-ketoacyl-ACP is a central intermediate in fatty acid biosynthesis, and disruptions to its formation or turnover can affect lipid homeostasis and cell viability. In some organisms, related beta-ketoacyl-ACP intermediates also participate in polyketide biosynthesis.