Release of Cell-Associated Concanavalin A by Methyl alpha-d-Mannopyranoside Reveals Three Binding States of Conceanavalin-A Receptors on Mouse Fibroblasts

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Abstract
Based on the partial reversibility of concanavalin A [ConA] binding by saturating concentrations of methyl .alpha.-D-mannopyranoside (MeManp) 3 states of cellular association could be characterized: type I, most rapidly established and most tightly bound, not released by MeManp at 0.degree. C or at 37.degree. C; type II, most loosely bound, released by MeManp at 0.degree. C, therefore not critically dependent on the temperature at which the release reaction is performed; type III, intermediate strength of binding, released by MeManp only at 37.degree. C, thus reflecting the temperature-sensitive nature of these cell complexes. A similar temperature dependence was found for cell-bound concanavalin A when it was displaced by an excess of the same lectin. The types of binding are seen irrespective of the temperature at which the cellular association was established. About 10% of the concanavalin A molecules bind to receptor structures in a saturable way and represent the type I association. Type I association is clearly distinct from types II and III. Type II seems to be the precursor of type III. Most of the type II associations can be converted into type III associations since ConA-cell complexes originally sensitive to the action of MeManp at low temperature gradually do become resistant after prolonged association at the same temperature. The temperature dependence in binding to cells was not related to receptor mobility since glutaraldehyde-trated cells had most of the release properties that were observed in untreated cells and which did not markedly differ between 3T3 cells and their SV40-transformed counterparts. In contrast to cellular binding, dissociation of concanavalin A from Sephadex beads by saturating concentrations of MeManp was complete irrespective of temperature.