Cyclic nucleotide-dependent phosphorylation in Dictyostelium discoideum amoebae.

Stimulation of Dictyostelium discoideum amoebae with cAMP was found to induce the specific phosphorylation of a 47,000 molecular weight protein (pP47). This cellular response to cAMP was developmentally regulated. It was first detected in 3 1/2-h starved cells and appeared to persist throughout the aggregation phase of the cells' life cycle. pP47 phosphorylation was specifically induced by cAMP in that amoebae did not respond to stimulation with 5'-AMP, folic acid, Ca2+, and/or the Ca2+ ionophore A23187. cGMP could elicit pP47 phosphorylation but only at high concentrations. Phosphorylation of pP47 in response to cAMP occurred rapidly (within 5 s). The length of time for which it remained phosphorylated depended upon the concentration of the stimulus. With 10(-6) M cAMP, pP47 was phosphorylated for less than 4 min. If amoebae were stimulated with 10(-4) M cAMP, over 30 min were necessary before pP47 was dephosphorylated. Once dephosphorylated, pP47 could again be phosphorylated upon reapplication of the cAMP stimulus.