Selective release of inner core proteins from intestinal microvillus membrane by lithium diiodosalicylate

Lithium diiodosalicylate (LIS) was used to selectively solubilize proteins from purified intestinal brush border membrane vesicles. Incubation of the vesicles with increasing concentrations of LIS resulted in the progressive release of proteins with total disruption of the membranes being obtained at 200 mM. Maximum selectivity was observed at 20-30 mM LIS which preferentially released actin and other non-glycosylated proteins while all the glycoproteins remained associated with the membrane. Electron micrographs showed that, after LIS treatment, brush border vesicles are partially disrupted and have lost their inner core of microfilaments. Sucrase, trehalase, leucylnaphthylamide hydrolase, gamma-glutamyl transpeptidase and alkaline phosphatase all retained more than 70% of their activities and remained associated with the membrane fraction after LIS solubilization (30 mM). The results indicate that lithium diiodosalicylate treatment provides an efficient method for the separation of cytoskeletal proteins from intrinsic membrane glycoproteins and should be very useful for the purification of microvilli proteins and for the study of membrane-protein interactions.