Endogenous cell surface lectin in Dictyostelium: Quantitation, elution by sugar, and elicitation by divalent immunoglobulin

Abstract

The amount of total endogenous cellular and cell surface lectin in aggregating Dictyostelium purpureum was determined by a number of immunochemical techniques. The results show that of the 5 × 106 molecules of the lectin (called purpurin) per aggregating cell only about 2% (1 × 105 molecules) is present on the cell surface. Cell surface purpurin can be specifically eluted by lactose, which indicates that it is held to the surface by its carbohydratebinding site. The eluted purpurin is replaced on the cell surface within 45 min. Estimates of cell surface purpurin made by binding of specific immunoglobulin to the cells at 4°C indicate that a much larger amount, about 1 × 106 molecules, becomes associated with the cell surface in the presence of this divalent ligand. In contrast, univalent antibody fragments do not have this effect. © 1980, Rockefeller University Press., All rights reserved.