cAMP,-induced changes in cAMP-binding sites on D; discoideum amebae

Abstract

Cell surface levels of 3H-cAMP binding to Dictyostelium discoideum amebae are dramatically reduced when cells are preincubated with cAMP. This decrease in 3H-cAMP binding is shown to reflect a loss in the number of binding sites and not in any significant change in their affinity constants(s). cAMP-mediated loss of its binding sites requires the continued presence of the cyclic nucleotide and does not depend upon protein synthesis. Reapparition of sites, which occurs when cAMP is eliminated from the media, also does not depend upon protein synthesis. Experiments using metabolic inhibitors and heat-killed cells suggest that the loss of binding sites is a direct consequence of the formation of cAMP-binding protein complexes.