Stereospecificity for oligosaccharides of two receptor sites in a labellar sugar receptor of the fleshfly

Responses of a single sugar receptor to oligosaccharides, such as turanose, palatinose, cellobiose, trehalose, maltotriose, melezitose, and raffinose, were depressed almost completely after 3 min treatment with 0·5 mM p-chloromercuribenzoate (PCMB). In the same preparation, responses to d-glucose were depressed in the same manner, but those to d-fructose were hardly affected after PCMB treatment. This may indicate that these oligosaccharides do not react with a furanose site but react only with a pyranose site. The stereospecificity for these oligosaccharides of the sugar receptor are discussed. The response to 4 M d-mannose, a very weak stimulative sugar, was almost completely depressed after PCMB treatment, which suggests that a stimulative fraction of d-mannose reacts with the pyranose site in spite of its inhibitory effect on fructose stimulation.