Evidence for the existence of two types of cAMP binding sites in aggregating cells of Dictyostelium discoideum.

Inhibition by dithiothreitol of the cell-bound phosphodiesterase has allowed the measurement of cAMP binding to aggregation-competent Dictyostelium discoidium amebae. Two classes of binding sites were demonstrated: Type 1, of low affinity (Kd approximately 160 nM) and high capacity (Ro approximately 1 X 10(5) sites per cell); and Type 2, of high affinity (Kd approximately 9 nM) but low capacity (Ro approximately 1.5 X 10(4) sites per cell). Both sites are developmentally regulated and are expressed during aggregation. The specificities of both sites are consistent with the specificity observed in vivo for the chemotactic response.