Guanine nucleotides modulate the function of chemotactic cyclic AMP receptors in Dictyostelium discoideum.

Guanosine di- and triphosphates specifically decrease the affinity of chemotactic cAMP receptors in isolated Dictyostelium discoideum membranes. The K0.5 was increased from 50 nM to 150 nM. Receptors were shown to be heterogeneous in dissociation kinetics. In the absence of guanine nucleotides three dissociation processes could be resolved, having first order rate constants of 8.7 X 10(-4), 1.3 X 10(-2), and higher than 0.1 s-1. Guanine nucleotides decreased the affinity for cAMP by transforming the slowest dissociating receptor form (KD is 8 nM) to forms dissociating more rapidly. Our data indicate that a guanine nucleotide binding protein (G-protein) is involved in the transduction of the cAMP signal in D. discoideum.