Comparison of synaptic plasma membrane and synaptic vesicle polypeptides by two-dimensional polyacrylamide gel electrophoresis.

Extracts of chick brain synaptic plasma membranes, synaptic vesicles, and mixtures of membranes and vesicles were examined by electrophoresis on two-dimensional polyacrylamide gels by a modification of the O'Farrell technique. Synaptic plasma membranes had twenty-one major polypeptides; synaptic vesicles had seventeen. Thirteen major polypeptides were common to both fractions. The similarities between the synaptic vesicle and synaptic plasma membrane patterns are unlikely to be due to contamination of one fraction by the other or to contamination of both fractions by microsomes, synaptoplasm or mitochondria. Our findings are consistent with mixing of membrane proteins occurring during exocytosis but it remains to be shown that these synaptic subfractions are not contaminated by a type of membrane for which markers are not yet available.