Figure 2. Drosophila melanogaster Gyc-89Da forms an active guanylyl cyclase when co-expressed with Gyc-88EL. Extracts from COS-7 cells that were transiently transfected with the guanylyl cyclase subunits shown were assayed from guanylyl cyclase activity in the presence of either Mg2+ (open bars) or Mn2+ (solid bars). All extracts showed higher levels of activity in the presence of Mn2+ compared to Mg2+. When Gyc-89Da was co-expressed with either conventional guanylyl cyclase subunit, Gyc-99B or Gyc-100B, no enzyme activity was detected above vector transfected controls. By contrast, when Gyc-89Da was co-transfected with Gyc-88EL, higher levels of guanylyl cyclase activity was measured compared to cells transfected with Gyc-88EL alone. Each bar represents the mean ± SEM. of 3 determinations.