Membrane protein and glycoprotein composition of beef brain synaptic vesicles

Synaptic vesicles were isolated from adult bovine cortical gray matter by differential centrifugation and membrane filtration of a hypoosmotically lysed crude mitochondrial fraction. Vesicle preparations were analyzed for purity by electron microscopy and enzyme assays. Polyacrylamide gel electrophoresis of SDS-solubilized and 2-mercaptoethanol-reduced vesicle membrane proteins revealed 4 major proteins with molecular weights ranging from 17,000 to 60,000, and about 10 minor proteins with molecular weights up to 170,000. The protein profile of the Triton X-100-extracted vesicle membranes was less complex, with 1 major protein and 5 minor bands. The major protein of the Triton extract was identified as a glycoprotein with a molecular weight of 45,000. Two additional minor PAS-positive bands were seen, with molecular weights of 78,000 and 95,000.