aminobutanol stimulated the incorporation [CH3-14C]methionine
into the phospholipid fraction. However, stimulation of incorporation
of radioactivity did not occur with diethanolamine, diethylethanolamine
or dimethylaminoisopropan-2-ol. However, N-isopropylethanolamine
was converted into phosphatidylisopropylethanolamine that was
methylated to form phosphatidyl-N-methylisopropanolamine [32].
Thus, the head group specificity of PEMT appears to have some flexibility
but whether or not any of these alternative bases would be exposed
to PEMT in vivo is doubtful. PE plasmalogen does not appear to be a substrate
for methylation by PEMT (M. Hermansson, R. Jacobs, D. E. Vance,
unpublished results). Presumably these observations reflect PEMT activity,
but experiments with purified enzyme have not been reported.