High affinity Ca2+-stimulated Mga+-dependent ATPase activity of nerve ending particles (!vnaphmm) from rat brain tissue appears to be associated primarily with isolated synaptic plasma membranes. The synaptic membrane (Ca2+ + Mga+)-ATPase activity was found to exhibit strict dependence on Mg+ for the presence of the activity, a high affinity for Ca2+ (&.a = 0.23 NM), and relatively high affini...