Oleoyl-phosphatidylcholine molecular species desaturated in pea leaf microsomes — possible substrates of oleate-desaturase in other green leaves

Abstract

Eleven phosphatidylcholine (PC) molecular species were identified in pea leaf microsomes: predominant species were 16:0 18:2 (28 mol%), 18:2 18:2 (21%), 18:3 18:2 (18%) and 16:0 18:3 (16%). When pea leaf microsomes were incubated with [ 14C]oleoyl-CoA in absence of any NADH, four labelled PC molecular species were formed: 1–18:3-2[ 14C]18:1 PC (23%), 1–18:2-2[ 14C]18:1 PC (37%), 1–16:0–2[ 14C]18:1 PC (33%) and 18:1/[ 14C]18:1 PC (3%). All these labelled molecular species were possible substrates for pea leaf desaturase. When NADH was added to the incubation medium, labelled oleoyl-PC molecular species appeared for the first 10 min of incubation and their labelling then progressively declined. The labelling of linoleoyl-PC molecular species regularly increased during incubation; the molecular species produced by oleate desaturase were: 1–18:3-2[ 14C]18:2 PC (17%), 1–18:2-2[ 14C]18:2 PC (48%), 1–16:0–2[ 14C]18:2 PC (20%) and 18:1 [ 14C]18:2 PC (traces). The three main labelled species were obtained in vivo, with entire pea leaves, starting from ammonium [ 14C]oleate. Esterification of [ 14C]oleoyl-CoA into PC molecular species was followed in the microsomes from sunflower, safflower and spinach leaves. Although the same molecular species as those found previously in pea were labelled, great differences in the quantitative distribution of [ 14C]oleyl residues among PC molecular species were observed.