On the phospholipid metabolism of glial cell primary cultures. III. Utilization of 1-alkenyl-glycerophosphoethanolamine (lysoplasmalogen).

Primary cultures prepared from newborn rat brain, consisted after 16 or 17 days mainly of astrocytes and of oligodendrocytes. 1-Alkenyl-sn-glycero-3-phosphoethanolamine (lysoplasmalogen) was used as substrate for studies on the metabolism of ethanolamine-glycerophospholipids. After 3 hr incubation two main products were observed: a) 1-alkenyl-2-acyl-sn-glycero-3-phosphoethanolamine (= ethanolamine plasmalogen) and b) 1-alkenyl-2-acyl-sn-glycero-3-phosphocholine (= choline plasmalogen). The acylation rate reached saturation at about 10 nmol substrate/mg cell protein with a Vmax of 30 nmol x mg cell protein-1 x 3 hr-1. This acylated compound amounted to almost 60% of all radioactivity internalized, whereas the second product, choline plasmalogen, came to 20%. Unchanged substrate was found within the cells only in small amounts, even at maximum substrate internalization. These results were discussed in comparison with those obtained with 1-alkyl-sn-glycero-3-phosphoethanolamine under the same conditions (25).

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.