Identification and Characterization of the Major Proteins of Mammalian Brain Synaptic Vesicles

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Abstract
Highly purified rat and cow brain synaptic vesicles contain major proteins with molecular weights of .apprx. 74,000, 60,000, 57,000, 40,000, 38,000, and 34,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The presence of the major proteins on synaptic vesicles was confirmed by immunoprecipitation of intact rat brain synaptic vesicles with a synaptic vesicle-specific monoclonal antibody. The 40,000-M protein appeared to be identical to the 38,000-Mr integral membrane glycoprotein, p38 or synaptophysin, previously identified as a major componet of mammalian synaptic vesicles. The isoelectric point of the 75,000-Mr proteins from either rat of chow brain synaptic vesicles is 5.0, and the pI of the 57,000-Mr protein is .apprx. 5.1 in both species. The similarityin size and charge of several major proteins in rat and cow synaptic vesicles suggests a high degree of structure conservation of these proteins in diverse mammalian species and raises the possibility that a set of functions common to most or all mammalian synaptic vesicles is mediated by these proteins.