Partial purification of a phosphoethanolamine methyltransferase from rat brain cytosol.

The conversion of phosphoethanolamine to phosphocholine requires 3 separate N-methyltransferases. We had previously purified the enzyme catalyzing the last methylation, phosphodimethylethanolamine N-methyltransferase. We have successfully purified the enzyme catalyzing the initial methylation of phosphoethanolamine. A 434 fold purified enzyme from rat brain was obtained by the sequential use of ammonium sulfate fractionation, Q-Sepharose fast flow column chromatography and a omega-aminoethyl agarose column chromatography. The pH optimum was 11 or greater, the Km value for phosphoethanolamine was 167.8 +/- 41.7 microM and the Vmax was 487.3 +/- 85 mmoles/mg/hr. The kinetics for S-adenosyl-methionine, the methyldonor, has characteristics of cooperative binding with a Km of 1.805 +/- 0.59 mM and a Vmax of 16.9 +/- 3.6 mumoles/mg/hr. The activity was stimulated 6 fold by 2.5 mM MnCl2 and inhibited by DZA and S-adenosylhomocysteine. These results reinforce the early in vivo observations which had provided suggestive evidence for the existence of a pathway for the methylation of phosphoethanolamine to phosphocholine in rat brain.