Membrane‐Bound Cyclic AMP Phosphodiesterase in Chemotactically Responding Cells of <i>Dictyostelium discoideum</i>

Abstract

In cells of the cellular slime mold, Dictyostelium discoideum , that respond chemotactically to cyclic AMP, cell‐bound cyclic AMP phosphodiesterase was studied under two conditions: in suspensions of living cells with external cyclic AMP as a substrate, and in the 27000 × g sediment of cell homogenates. Under both conditions a drastic increase of cell‐bound phosphodiesterase activity in the developmental phase preceding cell aggregation was found. In non‐aggregating mutants this increase is smaller or absent. The particle‐bound cyclic AMP phosphodiesterase has an optimum at pH 7.0–8.0. In vivo it is resistant to inhibition by external glutathione and to a macro‐molecular phosphodiesterase inhibitor from Dictyostelium discoideum ; in particle fractions enzyme activity is partially sensitive to these inhibitors. A possible function of this enzyme in the chemo‐tactic receptor system is discussed.