Synaptic vesicles contain an ATP-dependent proton pump and show 'knob-like' protrusions on their surface.

Synaptic vesicles from guinea pig brain were highly purified by chromatography on Sephacryl S 1000. They were associated with a Mg-ATPase which could be solubilized with dichloromethane from vesicle membranes, and which elutes upon gel filtration with a mol. wt. approximately 300 kd. Vesicles accumulate [14C]methylamine in the presence of external ATP, indicating an ATP-dependent proton pump. Electron microscopy using a quick freeze, deep etch, rotary shadowing technique showed characteristic 'knob-like' protrusions on the surface of the vesicle. We suggest that these protrusions represent part of a proton ATPase which may be necessary for packaging of neurotransmitter into synaptic vesicles.