Antagonists of chemoattractants reveal separate receptors for cAMP, folk acid and pterin in Dictyostelium

Adenosine 3′,5′-monophosphate (cAMP), folic acid and pterin are chemoattractants in the cellular slime molds. The cAMP analog, 3′-amino-cAMP, inhibits a chemotactic reaction to cAMP at a concentration at which the analog is chemotactically inactive. The antagonistic effect of 3′-amino-cAMP on the chemotactic activity of cAMP is competitive, which suggests that 3′-amino-cAMP antagonizes cAMP via the chemotactic receptor for cAMP. 3′-Amino-cAMP does not antagonize folic acid or pterin. The binding of folic acid to post-vegetative Dictyostelium discoideum cells is inhibited by low concentrations of 2-deamino-2-hydro folic acid (DAFA 7]). DAFA is neither chemotactically active, nor does it inhibit a chemotactic reaction to folic acid. This questions the involvement of the main folic acid cell surface-binding sites in the chemotactic response to folic acid. The pterin analog, 6-aminopterin, is an antagonist of pterin, but not of cAMP or folic acid. Our results show that cAMP, folic acid and pterin are detected by different receptors. Furthermore, they suggest that the antagonistic action of 3′-amino-cAMP and 6-aminopterin is localized in the signal transduction pathway at a step before the signals from the separate receptors have arrived at a single pathway.