| Abstract: | Experiments involving the co-incubation of wild type (A3) cells of Dictyostelium discoideum and a spontaneous aggregation-minus mutant (HW 2) suggested that the mutant was defective in cellular interactions. The inhibition of A3 development by HW 2 cells and the differentiation of a small fraction of HW 2 cells which is allowed by A3 cells, both depend on cell contact. Therefore, we compared cell surface molecules in vegetative A3 and HW 2 cells by a variety of techniques to determine whether defects in HW 2 could be found prior to the inhibition of development in vegetative amoebae. Antigenic defects, or differences in binding of concanavalin A, or both, were localized to three plasma membrane macromolecules using glutaraldehyde-fixed sodium dodecyl sulfate gels of plasma membranes. Two periodic acid-Schiff-positive glycoproteins, and one glycolipid also differed in HW 2. Three glycoproteins had an increased sensitivity to pronase in isolated plasma membranes suggesting an alteration in their topography. Glycoprotein E, the major glycoprotein of vegetative plasma membranes is abnormal in topography, altered as a concanavalin A receptor, and is antigenically abnormal. |
