Metabolism of different monoacylphospholipids in isolated hepatocytes and the intact rat

The 1-[3H] palmitoyl, 2-[3H] oleoyl, and 2-[14C] linoleoyl derivatives of sn-glycero-3-phosphoethanolamine and the corresponding derivatives of sn-glycero-3-phosphocholine were injected intraportally to rats and their incorporation into liver lipids was studied 15 min thereafter. Both the uptake by the liver and the degree of acylation was higher for the unsaturated compounds. The uptake of lysophosphatidylethanolamine was higher than that of lysophosphatidlycholine. The metabolism of 1-lysophosphatidylethanolamine was also studied in isolated hepatocytes. The degree of hydrolysis was much more prominent than in vivo. After injecting 2-[14C] linoleoyl derivatives, a large part of the 14C was recovered in the dienoic phospholipids. Subfractionation by reversed-phase partition chromatography showed that the isotope was located in the palmitoyllinoleoyl and stearoyl-linoleoyl fraction. The 100 X stearoly/(palmitoyl + stearoyl) ratio was 84 in dienoic phosphatidylethanolamine and 59 in dienoic phosphatidylcholine. This preference for stearic acid is significantly larger than in other pathways yielding dienoic phospholipids. It can be concluded that the monoacylphospholipid acyltransferase reactions operating at positions 1 or 2 yield different saturated acyl chain profiles in phosphatidylethanolamine and phosphatidylcholine of a specific unsaturation. This may be important in the regulation of the fatty acid composition of the membrane phospholipids.