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 back‐bone 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. Copyright © 1993, Wiley Blackwell. All rights reserved