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 (18:3(Delta9Z ,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 Delta(12)-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 Delta(12)-position of linoleic acid or gamma-linolenic acid, but not in alpha-linolenic acid, into a conjugated cis-trans double bond system.