Biosynthesis of γ-linolenic acid in developing seeds of borgae (Borago officinalis L.)
Résumé
Δ6-desaturation of [14C]linoleoyl-CoA or [14C]oleoyl-CoA leading to the synthesis of γ-linolenic acid was studied in vitro with microsomal fractions from developing seeds of Borago officinalis. Time course of the reaction, effects of protein and precursor concentrations and nucleotide requirements were examined. These parameters allowed us to improve the in vitro Δ6-desaturation assay. We observed that the precursors were acylated mainly in phophatidylcholine, dyacylglycerol and triacylglycerol, and then desaturated. NADH was absolutely required when [14C]oleoyl-CoA was the percursonr, but not when [14C]lionleoyl-CoA was the precursor although it stimulated the reaction. The in vitro Δ6-desaturate activity was found mainly in phosphatidylcholine, associated with enriched endoplasmic reticulum membranes (ER) from embryos. No activity was observed in ER from seed coat or seedling. During maturation of the seeds, Δ6-desaturase reached its highest activity 14 to 16 days after pollination.
