Activites of Enzymes Synthesizing Diacyl, Alkylacyl, and Alkenylacyl Glycerophosphoethanolamine and Glycerophosphocholine During Development of Chicken Brain

Abstract: Ethanolamine and choline glycerophospholipids are the major phospholipids of brain membranes. During brain development, the accumulation of these phospholipids is most intense when myelination occurs. In order to gain knowledge about the regulatory mechanisms for synthesis of these lipids in relation to membrane synthesis, we investigated the activities of the 1,2‐diradyl‐sn‐gIycerol: CDPethanolamine phosphoethanolarnine transferase and 1,2‐diradyl‐sri‐glycerol:CDPcholine phosphocholine transferase during chicken brain development. Diacyl, alkenylacyl, and alkylacylglycerols are substrates for both enzymes. The specific activities of microsomal phospho‐ethanolamine and phosphocholine transferases are constant between the 8th and 18th day of embryonic life. The specific activities of both enzymes double around hatching, which is the period of intense myelination and marked ac‐cumulation of ethanolamine and choline glycerophospholipids in brain. At the same time, the amount of microsomes increases by 50%; thus the total activities increase threefold. Four days after hatching the specific activities of both enzymes are at adult values. Similar results were obtained in the presence of exogenous diacyl or alkylacylglycerols. During brain development the apparent Km, value of rnicrosomal phosphoethanolamine transferase for CDP ethanolamine increases when assayed with diaclyglycerols or alkylacyl‐glycerols a s lipid substrates. The apparent Km, value of phosphocholine trans‐ferase for CDP choline does not change during brain development in the presence of exogenous diacylglycerols, but increases in the presence of exogenous alkylacylglycerols. These changes in Km, values may be due to the appearance of glial isoenzyme at the beginning of myelination. The apparent Km, values of diacylglycerol phosphocholine, alklyacylglycerol phosphocholine, and diacyl‐glycerol phosphoethanolamine transferases for their CDP bases are similar in adult brain microsomes and are threefold higher than the apparent Km, value of alkylacylglycerolphosphoethanolamine transferase. The high affinity of alkylacylglycerolphosphoethanolamine transferase for CDPethanolamine may be responsible for the preferential synthesis of ethanolamine plasmalogens in brain.