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

Based on the partial reversibility of concanavalin A binding by saturating concentrations of methyl α‐ d ‐mannopyranoside (MeMan p ) three states of cellular association could be characterizaed; type I, Most rapidly established and most tightly bound, not released by MeMan p at 0°C or at 37 °C; type II, most loosely bound, released by MeMan p at 0°C, therefore not critically dependent on the temperature at which the release reaction is perormed; type III, intermediate strength of binding, released byh MeMan P only at 37°C, thus reflecting the temperature‐sensitive nature of these cell complexes. A similar temperature dependence was found for celll‐bound concanavalin A when it was displayced 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 sturable way and represent the type I association. Type I association is clearly distinct from types II and III. Type II seems to be the porecursor of type III. Most of the type II associations can be converted into type III assciations since ConA‐cell complexes originally sensitive to the action of MeMan p at low temperature gradualy do become resistant after prolonged association at the same temperature. The temperature dependence in binding to cells was, however, not related to receptor mobility since glutaraldehyde‐treated cells had most of the release properties that were observed in untreated cells and which did not markedly differ between 3T3 cells and therir SV40‐transformed counterparts. In contrast to cellular binding, didsociationof concanavalin A from Sephadex beads by saturating concentrations of MeMan p was complete irrespective of temperature.