Characterization of phospholipid methylation in rat brain myelin

Highly purified rat brain myelin was solubilized in Triton X-100 and myelin phospholipid N-methyltransferase was characterized. The enzyme activities were separated by isoelectric focusing and ion-exchange chromatography. The phospholipid methyl-transferase has shown at least four peaks of activity with pIapp. values of 4.5, 5.2, 6.2 and 8.4. After affinity purification each of these activities revealed a close set of bands of approx. 65 kDa on SDS/PAGE. These data together with those from preparative SDS/PAGE separations suggested that rat brain myelin contains three acidic and at least one basic phospholipid-methylating isoenzymes and that the major isoenzyme in each case is approx. 65 kDa in size. While the predominant product of the reaction catalysed by all detected isoforms was monomethylated phosphatidylethanolamine, the least acidic isoform (pIapp. 6.2) also formed about 20% phosphatidylcholine, suggesting that these isoenzymes may play different roles in vivo.