title: Specific labeling of glycoproteins in yeast plasma membrane with concanavalin A.
abstract: The intramembranous particles of yeast Saccharomyces cereisiae plasma membrane form paracrystalline arrays or are randomly distributed as seen by freeze-fracture electron microscopy. Protoplasts with randomly distributed particles and with paracrystalline arrays were isolated and subsequently labeled with 3H-Con A, Con A and ferritin-Con A. The distribution of the Con A or the ferritin-Con A molecules on deep-etched exoplasmic surfaces strongly resembled the distribution of the intramembranous particles. The influence upon labeling of buffer ionic strength was investigated. Binding assays with 3H-Con A and freeze-etch electron microscopy demonstrated that the amount of non-specifically bound lectin molecules decreases by increasing buffer ionic strength. Only partial removal of Con A molecules was achieved by adding various concentrations of the specific sugar Methyl-alpha-D-Mannoside (alpha MM) to labeled protoplasts. By means of analytical ultracentrifugation it was found that alpha MM also promotes the formation of Con A dimers. fixed protoplasts were treated with detergents and 2-chloroethanol at various concentrations and subsequently labeled with 3H-Con A or ferritin-Con A. The amount of Con A bound to extracted cells did not decrease but ultrastructural changes of the deep-etched surfaces were observed. From our data it can be concluded that only the glycoproteins are labeled with Con A and they seem to be associated with the intramembranous particles [15]. Each intramembranous particle seems to bind 36 to 44 Con A molecules and therefore the glycoproteins seem to possess very long sugar chains. This further supports the hypothesis that the intramembranous particles are associated with the membrane-bound invertase.
mesh_terms: D002462:Cell Membrane / Q000648:ultrastructure; D003208:Concanavalin A / Q000378:metabolism; D005293:Ferritins; D005613:Freeze Etching; D006023:Glycoproteins / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D011952:Receptors, Concanavalin A / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000648:ultrastructure*
chemical_list: D006023:Glycoproteins; D008565:Membrane Proteins; D011952:Receptors, Concanavalin A; D003208:Concanavalin A; D005293:Ferritins