Base exchange reactions of the phospholipids in rat brain particles.

A particulate fraction from rat brain catalyzes the incorporation of [(14)C]choline, [(14)C]ethanolamine, and l-[(14)C]serine into phosphatidylcholine, phosphatidylethanolamine, and phosphatidylserine, respectively. The reaction appears to be energy-independent since Mg(2+), CTP, ATP, and NaF have no stimulatory action. The incorporation is inhibited by EDTA and activated by Ca(2+). The pH optimum for the incorporation of choline is 9.5, for ethanolamine it is 9.0, and for l-serine it is 8.5. Tris, bicine, and imidazole buffers are inhibitory. The incorporations are inhibited by a variety of structurally related alcohols and are stimulated by isoserine (alpha-hydroxy,beta-aminopropionic acid).