GTP = 3',5'-cyclic GMP + diphosphate Has also activity with Mn(2+) (in vitro). Activated by nitric oxide in the presence of magnesium or manganese ions. The active enzyme is formed by a heterodimer of an alpha and a beta subunit. Heterodimer with GUCY1B1. There are two types of guanylate cyclases: soluble forms and membrane-associated receptor forms. Belongs to the adenylyl cyclase class-4/guanylyl cyclase family.