Glucose-binding membrane proteins.

Abstract

To identify glucose-binding proteins amongst the polypeptides of the mouse duodenal brush border membrane, three types of experiments are reported. The first involved the introduction of labelled glucose and its analogue phlorizin into the lumen of separate groups of ligatured duodenal segments. Several proteins were shown to have bound both labelled species in situ by liquid scintillation counting of slices from polyacrylamide gels on which solubilised membrane protein had been electrophoretically separated. The second type of experiment was designed to determine the competitive nature of the binding of both labelled and cold phlorizin to proteins which had already bound glucose. Only three bands could competitively bind phlorizin. Finally, gels on which solubilised protein from in situ glucose-binding experiments had been run were placed in solutions containing labelled phlorizin. The binding of phlorizin to proteins in the same three bands as above suggested a confirmation of the conclusion that there were three membrane protein types which appeared to be involved in phlorizin-sensitive glucose-binding.