Isomeric sn‐1‐octadecenyl and sn‐2‐octadecenyl analogues of lysophosphatidylcholine as substrates for acylation and desaturation by plant microsomal membranes

Abstract

To provide supporting and independent evidence for lipid-linked desaturation of acyl groups in plant microsomal membranes, ether-analogous substrates were synthesized and used for in-vitro desaturation studies. The substrates included 1-O-(9-cis-octadecenyl)-sn-glycero-3-phosphocholine and 2-O-(9-cis-octadecenyl)-sn-glycero-3-phosphocholine as well as labelled 1-O-(9-cis-[9,10-3H2]octadecenyl)-sn-glycero-3-phosphocholine. In experiments with microsomal membranes from developing fruits of sunflower, it was shown that both isomeric alkenyl ether phospholipids were acylated with [14C]oleoyl-CoA and [14C]palmitoyl-CoA. In the presence of O2 and NADH, the oleoyl groups incorporated into both compounds, i.e. at the sn-1 and sn-2 positions of the glycerol backbone of the substrate, were desaturated to linoleoyl residues in similar proportions. Under the same conditions, an additional double bond, but not an enol-ether double bond, was introduced into the ether-linked side chain of acylated 1-O-(9-cis-[9,10-3H2]octadecenyl)-sn-glycero-3-phosphocholine. This represents the first demonstration of this type of desaturation with an alkenyl ether phospholipid and confirms previous conclusions that plants introduce second and further double bonds into lipid-linked acyl groups.