Formation of conjugated Δ11 Δ13 -double bonds by Δ12 -linoleic acid (1,4)-acyl-lipid-desaturase in pomegranate seeds.

For the biosynthesis of punicic acid (18:3Δ9Z ,11E ,13Z ) a (11,14)-linoleoyl desaturase activity has been proposed. To isolate this acyl-lipid-desaturase, PCR-based cloning was used. This approach resulted in the isolation of two complete cDNAs. The first isolated full-length cDNA harbors a sequence of 1350 bp encoding a protein of 395 amino acids. The second cDNA was 1415 bp long encoding a protein of 387 amino acids. For functional identification proteins encoded by the cDNAs were expressed in Saccharomyces cerevisiae , and formation of newly formed fatty acids was analyzed by gas chromatography-free induction decay (GC-FID) and GC/MS. The expression of the heterologous enzymes resulted in the first case in a significant amount of linoleic acid and in the second case, after linoleic acid supplementation, in formation of punicic acid. The results presented here identify one cDNA coding for a classical Δ12 -acyl-lipid-desaturase. The other one codes for a new type of (1,4)-acyl-lipid-desaturase that converts a cis double bond located in the Δ12 -position of linoleic acid or γ-linolenic acid, but not in α-linolenic acid, into a conjugated cis–trans double bond system. [ABSTRACT FROM AUTHOR]