Evidence for the Presence of CDP‐Ethanolamine: 1,2‐diacyl‐sn‐glycerol Ethanolaminephosphotransferase in Rat Central Nervous System Myelin

Abstract

Highly purified rat brain myelin isolated by 2 different procedures showed appreciable activity for CDP-ethanolamine: 1,2-diacyl-sn-glycerol ethanolaminephosphotransferase (EC 2.7.8.1). Specific activity was close to that of total homogenate and approximately 12-16% that of brain microsomes. Other lipid-synthesizing enzymes [3], cerebroside sulfotransferase, lactosylceramide sialytransferase and serine phospholipid exchange enzyme, had less than 0.5% the specific activity in myelin compared with microsomes. Washing the myelin with buffered salt or taurocholate did not remove the phosphotransferase; activity was lost from myelin and microsomes by treatment with Triton X-100. It resembled the microsomal enzyme in having a pH optimum of 8.5 and a requirement for Mn2+ and detergent, but differed in showing no enhancement with EGTA (ethyleneglycol-bis(.beta.-aminoethyl ether)N,N,N'',N''-tetraacetic acid]. The diolein Km was similar for the 2 membranes (2.5-4 .times. 10-4 M), but the CDP-ethanolamine Km was lower for myelin (3-4 .times. 10-5 M) than for microsomes (11-13 .times. 10-5 M). This enzyme may be able to utilize substrate from the axon in situ.