Canine cardiac microsomes were shown to incorporate the nitrogenous bases, serine, ethanolamine, and choline, into their respective phospholipids by the energy-independent, Ca2+-stimulated base-exchange reactions. The optimal Ca2+ concentration was 2.5 mM. Metal ions other than Ca2+ either inhibited or had no effect on the activities. La3+ and Mn2+ were both potent inhibitors. The pH optimum fo...
