EFFECT OF CONCANAVALIN A ON CELLULAR SLIME MOLD DEVELOPMENT: PREMATURE APPEARANCE OF MEMBRANE-BOUND CYCLIC AMP PHOSPHODIESTERASE

Summary: Concanavalin A delays aggregation of slime mold amoebae, apparently by interfering with the cells ' response to the chemotactic agent, cyclic AMP. Concanavalin A also induces the premature appearance in non-aggregating cells of a membrane-bound cyclic AMP phosphodiesterase normally found only at the time of aggregation. The appearance of this enzyme is not due to activation of an inactive form of the enzyme. After a period of vegetative growth as solitary amoebae, cells of Dictyostelium discoideum move together into multi-cellular aggregates each of which differentiates into a fruiting body. The attraction of the dispersed cells into aggregation centres is in response to cyclic AMP secreted by the amoebae (1). Malchow et al. (2) have demonstrated in D. discoideum the presence of a membrane-bound cyclic AMP phosphodiesterase (mPDE) which dramatically increases in activity just preceding aggrega-tion and then returns to very low levels after aggregation. These investigators suggest that this phosphodiesterase partici-pates both in the detection of cyclic AMP and the chemotactic response during cell aggregation. We present here a study showing that Concanavalin A (Con A), a plant lectin known to bind to carbohydrate determinants of cell surfaces (3-8), affects the process of aggregation in slime mold development