A novel cyclic AMP metabolism exhibited by giant cells and its possible role in the sexual development of Dictyostelium discoideum

In Dictyostelium discoideum cyclic AMP (cAMP) metabolism during macrocyst development, i.e., the sexual cycle of this organism, and in giant cells, i.e., fusion products from opposite mating-type cells, was investigated. The pattern of change in cAMP levels during macrocyst development differed considerably from that observed during fruiting-body formation, i.e., the asexual cycle. Giant cells produced and excreted considerable amounts of cAMP. Adenylate cyclase activity catalyzing cAMP production in giant cells was comparable to that of unfused cells. However, the activity of membrane-bound phosphodiesterase in giant cells was extremely low, and no extracellular phosphodiesterase was excreted. A phosphodiesterase inhibitory protein was secreted in excess by giant cells.