Identification of Synapse Specific Components: Synaptic Glycoproteins, Proteins, and Transmitter Binding Sites

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Abstract
Synaptic junctions (SJ) were prepared from rat synaptic plasma membranes (SPM) by extraction with Triton X-100 and density gradient centrifugation. These SJ were enriched in certain Concanavalin A (Con A) binding glycoproteins, the 52,000 MW postsynaptic density (PSD) protein and receptor sites for L-glutamate, L-aspartate, kainic acid (KA) but not quinuclidinyl benzilate (QNB). Various other membrane fractions were extracted by the same procedure. Those fractions prepared from light SPM and crude myelin contained identifiable synaptic junctions and were also highly enriched in the synaptic components. The SJ-like fraction from mitochondria did not contain any of the characteristic synaptic macromolecules. This fraction from microsomes contained levels of the 52,000 MW PSD protein and binding sites for L-glutamate and L-aspartate similar to true synaptic junctions, although the Con A binding glycoproteins and KA binding sites were nearly absent. On the basis of EM, the SJ-like fraction from microsomes did not contain structures recognizable as SJ. Con A binding glycoproteins and KA binding sites appear to be excellent markers for the SJ.