Multiple receptor proteins for sweet taste inDrosophila discriminated by papain treatment

Summary Treatment of the labellar chemosensory setae of the fruit fly,Drosophila melanogaster, with 0.1 % papain for 3 min induced a complete elimination of the taste nerve response to fructose (Fig. 1). Responses to other sugars examined were not affected (Table 1). Responses to 20 mM LiCl and 0.1 M NaCl also remained unchanged by the treatment. The experiment on the time-dependency of the papain treatment showed a clear difference in the proteasesensitivity between the response to fructose and to glucose and sucrose (Fig. 2). The treatment with 0.005% trypsin for 3 min produced the same results. The response to fructose which was eliminated with the papain treatment, was restored after 3 hrs. These findings reveal the presence of a specific receptor site for fructose and its protease-sensitive nature and suggest the involvement of multiple receptor proteins in the sugar receptor ofDrosophila.We thank Dr. A. Shiraishi for valuable suggestions for electrophysiological recordings. This work was supported in part by a Grant-in Aid for Scientific Research from the Ministry of Education, Science and Culture of Japan.