The incorporation of phosphorylethanolamine into the phospholipids of brain microsomes in vitro

Abstract

Abstract Synthesis of ethanolamine phosphoglycerides (EPG) from labeled 14 C‐phosphorylethanolamine (PE) and cytidine triphosphate (CTP) has been studied in vitro in particles and in soluble fractions of chicken brain. The microsomal membranes can carry out this conversion, but supplementing the microsomes with an enzymic fraction derived from the particle‐free supernatant results in a noticeable increase of the rate of EPG synthesis. Mitochondria are almost inactive, in this connection. The conversion of PE to lipid is very low, in no case exceeding 0.5–0.6%, even in the presence of diacyl glycerols or 1‐alkenyl 2‐acyl glycerol. No stimulation occurs by supplementing the incubation system with natural lipid acceptors, intermediates of lipid synthesis, energy‐producing cofactors or monoacyl sn ‐glycero‐3‐phosphorylethanolamine (GPE), monoacyl sn ‐glycero‐3‐phosphorylcholine (GPC) and other lipid material. From these and other results, the conclusion is made that the PE:CTP cytidylyltransferase (E.C. 2.7.7.14) must display very low activity in vitro, thus limiting the overall rate of synthesis from PE. Diacyl GPE is the only lipid which has been found labeled after incubation with PE of the brain preparations. A small synthesis of alkenyl acyl GPE takes place, only when PE is incubated with suitable concentrations of a plasmalogenic diglyceride.