title: Evidence for the existence of two types of cAMP binding sites in aggregating cells of Dictyostelium discoideum.
abstract: 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.
mesh_terms: D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000378:metabolism; D001665:Binding Sites; D001667:Binding, Competitive; D002462:Cell Membrane / Q000378:metabolism; D002633:Chemotaxis; D000242:Cyclic AMP / Q000378:metabolism*; D006152:Cyclic GMP / Q000494:pharmacology; D003864:Depression, Chemical; D004023:Dictyostelium / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism*; D004229:Dithiothreitol / Q000494:pharmacology; D007700:Kinetics; D009235:Myxomycetes / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: D000242:Cyclic AMP; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D006152:Cyclic GMP; D004229:Dithiothreitol