Phosphatidylcholine molecular species involved in gamma-linolenic acid biosynthesis in microsomes from borage seeds

Boraginaceae seeds are particularly rich in gamma-linolenic acid (6,9,12-oc tadecatrienoic acid, gamma-18:3), In microsomes, the analysis of phosphatid ylcholine (PC) molecular species by HPLC led to identification of 15 differ ent molecular species; among them 4 contained gamma-18:3, mostly at positio n 2 of sn-glycerol. Time courses of acylation and desaturation in PC molecu lar species mere examined when [C-14]oleoyl-CoA or [C-14]linoleoyl-CoA was provided as substrates to isolated microsomes. With [C-14]oleoyl-CoA or [C- 14]linoleoyl-CoA and in the absence of NADH, 3 main labelled PC molecular s pecies mere found: 18:2/[C-14]18:1, 16:0/[C-14]18:1 and 18:1/[C-14]18:1. Wh en NADH was present in the incubation medium, the fatty acids mere progress ively desaturated by the Delta 12- and Delta 6-desaturases successively (wi th [C-14]oleoyl-CoA as precursor) or by the Delta 6-desaturase alone (with [C-14]linoleoyl-CoA as precursor). In both types of experiments, 7 final de saturation products in microsomes were evidenced; among them, 3 contained r adioactive gamma-18:3, i.e. 18:2/[C-14]gamma-18:3, 18:1/[C-14]gamma-18:3 an d 16:0/[C-14]gamma-18:3. While the Delta 12-desaturase lead no specificity for position on the glycerol backbone, labelled gamma-linolenic acid was re covered exclusively in the sn-2 position.