Abstract
The presence of G-proteins, interacting with cAMP surface receptors, was investigated in vegetative cells, aggregation-competent cells, and migrating slugs of Dictyostelium discoideum. Our results indicate that G-proteins are present in all stages. In vegetative cells there is a limited number of cAMP receptors but no effect of GTPτS on cAMP binding could be detected; in addition, no effect of cAMP on GTPτS binding or GTPase activity was observed. In both aggregation-competent cells and slugs GTPτS inhibits cAMP binding, while cAMP stimulates GTPτS binding and high-affinity GTPase. Since the presence of G-proteins coupled to cAMP receptors could be demonstrated in slugs, the involvement of the effector enzymes adenylate cyclase and phospholipase C was investigated. The results show that adenylate cyclase activity is stimulated by GTPτS in both stages and that in cells from migrating slugs the Ins(1,4,5)P 3 production is increased upon stimulation with cAMP. The possible involvement of G-proteins in signal transduction during the slug stage of D. discoideum is discussed.
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