The monomethylethanolamine- and dimethylethanolamine-base exchange reactions of rat-brain microsomal fraction

The ability of crude rat-brain microsome preparations to convert DME and MME to their corresponding phospholipid was explored. In common with the other base-exchange reactions, the incorporations of DME and MME were stimulated by about 1-4 mM Ca2+, possessed slightly alkaline pH optima, were energy independent and were unaffected by exogenous phospholipids. The Km values were 0.97 mM and 0.5 mM and the Vmax values were 9.6 nmol/mg protein per h and 6.25 nmol/mg protein per h for DME and MME, respectively. The P3 fraction of the brain and heart had the highest specific activities of particles prepared from several tissues.