Phospholipid metabolism of glial cell primary cultures, IV. Metabolism of 1-alkenyl-sn-glycero-3-phosphoethanolamine between 1 and 20 hours incubation.

Primary cell cultures prepared from newborn rat brain were incubated on the 16th or 17th day with the substrate 1-([1-3H]-1-alkenyl)-sn-glycero-3-phosphoethanolamine (lysoplasmalogen) for 1-20 h. The internalization of the substrate into the cells depended on the incubation time as well as on the amount of substrate. At any given time the acylation reaction to 2-acyl-1-alkenyl-sn-glycero-3-phosphoethanolamine (plasmalogen) was the most important event amounting to nearly 50-60% of the total radioactivity incorporated. Unchanged substrate was found in only small amounts within the cells. During incubation, the formation of 2-acyl-1-alkenyl-sn-glycero-3-phosphocholine (choline plasmalogen) increased, reaching saturation after 6 h with nearly 40% of the total radioactivity within the cells. These results were compared with those previously obtained with the substrate 1-([1-3H]alkyl)-sn-glycero-3-phosphoethanolamine under the same conditions. The acylation of this substrate as well as its conversion to the choline-containing analogue had been observed. Furthermore plasmalogen formation was also determined as a slow enzyme reaction. Both series of experiments showed a high acylation rate of 1-alkenylglycerophosphoethanolamine and a slow desaturation rate of the 1-alkyl compound. Thus, the following pathway of plasmalogen formation is proposed: 1-alkyl-sn-glycero-3-phosphoethanolamine leads to 1-alkenyl-sn-glycero-3-phosphoethanolamine leads to 2-acyl-1-alkenyl-sn-glycero-3-phosphoethanolamine.