PARTIAL-PURIFICATION OF A PHOSPHOETHANOLAMINE METHYLTRANSFERASE FROM RAT-BRAIN CYTOSOL

The conversion of phosphoethanolamine to phosphocholine requires 3 sep arate N-methyltransferases. We had previously purified the enzyme cata lyzing the last methylation, phosphodimethylethanolamine N-methyltrans ferase. We have successfully purified the enzyme catalyzing the initia l methylation of phosphoethanolamine. A 434 fold purified enzyme from rat brain was obtained by the sequential use of ammonium sulfate fract ionation, Q-Sepharose fast flow column chromatography and a omega-amin oethyl agarose column chromatography. The pH optimum was 11 or greater , the Km value for phosphoethanolamine was 167.8 +/- 41.7 mu M and the Vmax was 487.3 +/- 85 mmoles/mg/hr. The kinetics for S-adenosyl-methi onine, the methyldonor, has characteristics of cooperative binding wit h a Km of 1.805 +/- 0.59 mM and a Vmax of 16.9 +/- 3.6 mu moles/mg/hr. The activity was stimulated 6 fold by 2.5 mM MnCl2 and inhibited by D ZA and S-adenosylhomocysteine. These results reinforce the early in vi vo observations which had provided suggestive evidence for the existen ce of a pathway for the methylation of phosphoethanolamine to phosphoc holine in rat brain.