1. Ehrlich ascites-cell extracts convert choline and ethanolamine approximately equally well into their respective phosphoryl derivatives. 2. Choline is a potent inhibitor of ethanolamine phosphorylation, but ethanolamine has little effect on choline phosphorylation. 3. 2,3-Dimercaptopropanol, cysteine and Ca2+ inhibit ethanolamine phosphorylation, but have no detectable effect on choline phosphorylation. 4. Choline-phosphorylating activity in Ehrlich ascites-cell extracts is more stable during storage than ethanolamine-phosphorylating activity. 5. Choline phosphorylation is stimulated in the presence of benzoylcholine, succinylcholine, butyrylcholine and propionylcholine, whereas ethanolamine phosphorylation is inhibited. This relationship is reciprocal: the compounds causing the greatest stimulation of choline phosphorylation bring about the greatest inhibition of ethanolamine phosphorylation.
