A magnesium-dependent guanylate cyclase in cell-free preparations of Dictyostelium discoideum.

Receptor-mediated regulation of guanylate cyclase is well-studied in intact Dictyostelium discoideum cells, but study of the enzyme in cell-free preparations has hampered. A major obstacle has been that in vitro guanylate cyclase activity could be detected only in the presence of unphysiological concentrations of Mn2+-ions. In this paper we report the identification of a guanylate cyclase in D.discoideum cell homogenates that has high activity with Mg2+-GTP. The enzyme is activated by non-hydrolyzable ATP and GTP analogues and inhibited by submicromolar concentrations of Ca2+-ions. We suggest that the presently identified enzyme is regulated in intact cells via cell surface receptors. The compounds that modulated the enzyme activity in vitro may reflect physiologically relevant regulation mechanisms.