Separation of two receptor sites in a single labellar sugar receptor of the flesh-fly by treatment with p-chloromercuribenzoate

A 3 min treatment of a single sugar receptor with 0·5 mM p-chloromercuribenzoate (PCMB) did not affect its response to d-fructose, but depressed completely its response to d-glucose. This is the first direct evidence of the presence of two different sites in the sugar receptor of the fly.No specific protection by d-glucose on PCMB treatment suggested that PCMB did not react at a glucose-binding site but did react at a specific site indispensable to simulation by d-glucose.Various sugars were examined and classified into two groups according to the effects of PCMB treatment on the sugar receptor. They correspond to those effective in the furanose and pyranose forms, respectively. The pyranose group was further divided into two subclasses according to the presence or absence of three successive equatorial hydroxyl groups regardless of their positions. The results are discussed in relation to the structures that are common to furanose stimulating sugars.