Taste response to 2,5-anhydro-D-hexitols; rigid stereospecificity of the furanose site in the sugar receptor of the flesh fly.

2,5-Anhydro-D-mannitol with a fixed furanose ring stimulated the sugar receptor of the flesh fly and reacted with the furanose site. This is the first direct evidence that a furanose can stimulate the sugar receptor and supports strongly the assumption that beta-D-fructofuranose is the only stimulatory component in the solution of D-fructose. Rigid stereospecificity of the furanose site in the sugar receptor is discussed according to the effectiveness of various synthetic 2,5-anhydro-D-hexitols and related compounds. At least four receptor sites are concluded to be in a single sugar receptor: a pyranose (P) site, a furanose (F) site, an aliphatic carboxylate (R) site and an aromatic amino acid (Ar) site.