CYTOCHEMICAL-LOCALIZATION OF GUANYLATE AND ADENYLATE-CYCLASE IN PHOTORECEPTOR CELLS OF THE FLY

In photoreceptor cells of invertebrates light triggers an enzyme casca de in which the phosphoinositide pathway is crucially involved. Likewi se, there is growing evidence of an important role of cyclic nucleotid es, too. To localize these enzymes able to catalyze the formation of c GMP and cAMP, the spatial distribution of guanylate cyclase (EC 4.6.1. 2) and adenylate cyclase (EC 4.6.1.1) was determined in photoreceptor cells of the fly. In photoreceptor cells of the blowfly (Calliphora er ythrocephala), the electron dense reaction product of guanylate cyclas e was found within the phototransducing region, the rhabdomeral microv illi and in the mitochondria. Staining was also observed throughout th e cytoplasm of the microvilli. With the same cytochemical method, reac tion product for adenylate cyclase was found on the tips of the photos ensory membrane, and not in the cytoplasm of the rhabdomeral microvill i. The results presented here further argue for an important role of o ne or possibly two cyclic nucleotides in the photoreceptor cells, and possibly in the process of phototransduction of invertebrates.