CHARACTERIZATION OF PHOSPHOLIPID METHYLATION IN RAT-BRAIN MYELIN

Highly purified rat brain myelin was solubilized in Triton X-100 and m yelin phospholipid N-methyltransferase was characterized. The enzyme a ctivities were separated by isoelectric focusing and ion-exchange chro matography. The phospholipid methyltransferase has shown at least four peaks of activity with pI(app). values of 4.5, 5.2, 6.2 and 8.4. Afte r 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 kD a in size. While the predominant product of the reaction catalysed by all detected isoforms was monomethylated phosphatidylethanolamine, the least acidic isoform (pI(app.) 6.2) also formed about 20% phosphatidy lcholine, suggesting that these isoenzymes may play different roles in vivo.