Heterodimers with Gyc-89Da and Gyc-89Db 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). Homodimer is slightly stimulated by the NO donor sodium nitroprusside (SNP) but not the NO donor DEA-NONOate or the NO-independent activator YC-1. Heterodimer also exhibits some stimulation, some compounds (SIN-1 and two of the NONOates) that were ineffective at stimulating Gyc-88E alone did stimulate the heterodimer. Homodimer, and heterodimer; with Gyc-89Db and Gyc-89Da, 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 15 or 16 and continuing through to stage 1. 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 third 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. Expressed in embryos, larvae and adults. There are two types of guanylate cyclases: soluble forms and membrane-associated receptor forms. Belongs to the adenylyl cyclase class-4/guanylyl cyclase family. Probable cloning artifact. Probable cloning artifact.