Synaptic plasma membrane glycoproteins: molecular identification of lectin receptors

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Abstract
Synaptic plasma membranes isolated from rat cerebral cortex reacted with concanavalin (Con A), wheat germ agglutinin (WGA), Lens culinaris phytohemagglutinin (LcH) and Ricinus communis agglutinin (RCA). Competition studies indicated that specific topographical relationships exist between receptors for Con A and LcH, and for WGA and LcH. Reaction of [125I]Con A with synaptic membrane proteins following polyacrylamide gel electrophoresis identified 8 distinct molecular weight classes of glycoproteins possessing receptor activity for Con A, ranging in apparent MW from 27,000-165,000. Each of these reacted to varying degrees with LcH, WGA and RCA, indicating that a diverse population of carbohydrate moieties was associated with each molecular-weight class of glycoprotein. Following gel electrophoresis, competition between lectins did not occur, suggesting that each lectin reacts with a distinct group of carbohydrates and that specific relationships between these groups are destroyed by the solubilization and electrophoretic procedure. Synaptic junctional complexes isolated by Triton-X100 extraction of synaptic membranes exhibited a simplified glycoprotein composition with only 3 major molecular weight classes of glycoproteins possessing receptor activity for Con A being present.