Abstract. Potential interactions between membrane components of rat brain synaptic vesicles were analyzed by detergent solubilization followed by size fractionation or immunoprecipitation . The behavior of six synaptic vesicle membrane proteins as well as a plasma membrane protein was monitored by Western blotting . Solubilization of synaptic vesicle membranes in CHAPS resulted in the recovery of a large protein complex that included SV2, p65, p38, vesicle-associated membrane protein, and the vacuolar proton pump. Solubilization in octylglucoside resulted in the preservation of interactions between SV2, p38, and rab3A, while solubilization of synaptic vesicles with Triton X-100 resulted in two predominant interactions, one involving p65 and SV2, and the other involving p38 and vesicle-YNAPTIC transmission is the primary basis of intercellular communication within the nervous system. Central to this process are the synaptic vesicles respon sible for the storage and exocytotic release ofneurotransmitter . The life cycle of a synaptic vesicle includes steps of biogenesis, exocytosis, and membrane recycling (for reviews see Kelly, 1988 ;Trimble et al ., 1991) . Synaptic vesicle components are synthesized in the cell body and transported down the axon to the presynaptic nerve terminal . Within the terminal, the vesicles are loaded with neurotransmitter and stored either adjacent to the presynaptic plasma membrane at the active zone, or in clusters associated with cytoskeletal elements . Stimulation of the nerve terminal results in calcium influx which effects fusion of the synaptic vesicles with the plasma membrane. After exocytosis, synaptic vesicle membrane components are selectively recovered from the presynaptic plasma membrane by endocytosis and are recycled within the nerve terminal into mature synaptic vesicles. A molecular description of these membrane trafficking events and their physiological regulation is required for a more detailed understanding of synaptic transmission .One approach toward understanding the molecular mechanisms involved in synaptic transmission has been to identify and characterize the components of the synaptic vesicle membrane. A number of proteins are localized to synaptic © The Rockefeller University Press, 0021-9525/92/02/761/15 $2 .00 The Journal of Cell Biology, Volume 116, Number 3, February 1992 761-775 associated membrane protein . The multicomponent complex preserved with CHAPS solubilization was partially reconstituted following octylglucoside solubilization and subsequent dialysis against CHAPS. Reduction of the CHAPS concentration by gel filtration chromatography resulted in increased recovery of the multicomponent complex . Examination of the large complex isolated from CHAPS-solubilized vesicles by negative stain EM revealed structures with multiple globular domains, some of which were specifically labeled with gold-conjugated antibodies directed against p65 and SV2 . The protein interactions defined in this report are likely to underlie aspects of neurotransmitter secre...

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