Synaptosomal plasma membrane (SPM) and other subcellular fractions were isolated from the forebrain of 1-day-old chickens by a procedure based on that of Davis and Bloom (16) and Cotman and Taylor (13). The procedure involves the centrifugation through a discontinuous sucrose gradient of a crude synaptosomal-mitochondrial fraction which has been lysed and weighted with iodonitrotetrazolium. SPM isolated by this method contains only small amounts of lysosomal or mitochondrial membranes and is practically devoid of contaminating microsomal membranes, as estimated by enzyme marker assays. The purity of chick-brain SPM prepared by this method is compared to the purity of chickbrain fractions obtained by two other laboratories, using different methods (4, 59). The SPM were extracted with Triton X-100 and all fractions solubilized in sodium dodecyl sulfate (SDS). The delipidated proteins of all fractions were subjected to SDS-polyacrylamide electrophoresis on slab gels and stained for protein. A distinct difference was observed between the patterns given by the Triton-soluble and-insoluble fractions. Electron microscopy of the synaptic junction fraction showed numerous junctional complexes.
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