ATP = 3',5'-cyclic AMP + diphosphate Binds 1 Mg(2+) ion per subunit (PubMed:25295175). Is also active with manganese ions (in vitro) (PubMed:11431477, PubMed:11447108). Homodimer (PubMed:11447108, PubMed:16403515, PubMed:25295175). Can also exist as monomer (PubMed:16403515, PubMed:25295175). Belongs to the adenylyl cyclase class-4/guanylyl cyclase family. The structures described in PubMed:16403515 and PubMed:25295175 corresponds to an inactive form, and displays a conformation that alters the position and orientation of the residues that are expected to bind the substrate and the catalytic metal ions.