Heterodimers with Gyc88E are activated in response to changing oxygen concentrations, alerting flies to hypoxic environments. Under normal oxygen concentrations, oxygen binds to the heme group and results in low levels of guanylyl cyclase activity. When exposed to reduced oxygen concentrations, the oxygen dissociates from the heme group resulting in activation of the enzyme. GTP = 3',5'-cyclic GMP + diphosphate Binds 1 or 2 heme groups per heterodimer. Probably not activated by nitric oxide (NO). Heterodimer exhibits some stimulation, compounds (SIN-1 and two of the NONOates) that were ineffective at stimulating Gyc-88E homodimer did stimulate the heterodimer. Heterodimer; with Gyc88E, in the presence of magnesium or manganese. Expressed in embryos in a segmental pattern in the ventral nerve cord (VNC) and in the brain, beginning at stage 13 and continuing through to stage 17. Colocalized with Gyc-89Db in several peripheral neurons that innervate trachea, basiconical sensilla and the sensory cones in the posterior segments of the embryo. Expression in wandering 3rd instar larvae is most prominent in a small cluster of cells located in the anterior medial region of each brain lobe. In the VNC, expression is found in scattered cells both laterally and at the midline. There are two types of guanylate cyclases: soluble forms and membrane-associated receptor forms. Belongs to the adenylyl cyclase class-4/guanylyl cyclase family.