concanavalin-a and dithiobis(succinimidylpropionate)

The ability of Dictyostelium discoideum amoebae to synthesize and secrete cAMP in response to exogenous cAMP is called cAMP signaling. Concanavalin A is a potent, rapid, noncompetitive inhibitor of this response, with the rate of inhibition consistent with its rate of binding. The concanavalin A does not deplete cellular ATP, alter cAMP binding to its surface receptors, or affect basal adenylate cyclase activity, but blocks the cAMP-stimulated activation of adenylate cyclase. Therefore, concanavalin A appears to inhibit a step between the receptor and the adenylate cyclase which is necessary for the transduction of the cAMP signal. Wheat germ agglutinin, a polyclonal antibody against an 80-kDa glycoprotein, four monoclonal antibodies against the amoebal surface, and a chemical cross-linking agent which reacts with cell surface primary amines also inhibit signaling. To determine the importance of cross-linking in the inhibition, succinylated concanavalin A and the unlinked, reactive portion of the chemical cross-linker were tested and found to be relatively ineffective inhibitors. Thus it appears that ligands capable of cross-linking molecules on the external surface of D. discoideum amoebae inhibit cAMP signaling. It is proposed that these cross-linking agents prevent membrane or cytoskeletal rearrangement and that this rearrangement must occur before the adenylate cyclase is activated.

Topics: Adenylyl Cyclases; Concanavalin A; Cross-Linking Reagents; Cyclic AMP; Dictyostelium; Dose-Response Relationship, Drug; Enzyme Activation; Lectins; Succinimides; Surface Properties; Time Factors; Wheat Germ Agglutinins