cis3enoylACP

cis3enoylACP refers to a cis-3-enoyl-ACP intermediate formed during bacterial fatty acid biosynthesis. In this context, ACP stands for acyl carrier protein, a small acidic protein that carries growing fatty acyl chains via a 4'-phosphopantetheine thioester linkage. The term cis-3-enoyl-ACP denotes an enoyl-ACP molecule with a cis double bond located at the third carbon of the attached acyl chain, distinguishing it from the more common trans-2-enoyl-ACP in earlier steps of the cycle. This intermediate is typically bound to ACP and not freely soluble in the cellular medium.

Biochemical role and pathway context. The cis-3-enoyl-ACP intermediate is produced in many bacteria by the action of FabA, which has both dehydratase and isomerase activities. FabA converts trans-2-enoyl-ACP to cis-3-enoyl-ACP, enabling the introduction of a cis double bond into the growing fatty acid. This cis double bond can be retained through subsequent elongation steps, often involving FabB, to yield monounsaturated fatty acids. The ability to generate cis double bonds via enoyl-ACP isomerization provides an alternative route to unsaturated fatty acid production that is distinct from desaturation by soluble enzymes found in some other organisms.

Occurrence and significance. cis-3-Enoyl-ACP is a key intermediate in the type II fatty acid synthase (FAS II) system prevalent in bacteria and some plants. It contributes to membrane fluidity and adaptability by allowing the biosynthesis of unsaturated fatty acids. Its study helps illuminate the regulatory balance between saturated and unsaturated lipid synthesis and the specific enzyme activities—such as FabA and FabB—that control this branch of fatty acid metabolism.