Fig. 2. Detection of LAP at the plasma membrane by neuraminidase. Cells expressing LAP, LAP-Lamp-1 or LAP-Limp-II were metabolically labelled for 15 minutes and chased for one hour. Subsequently, the cells were incubated for one hour on ice with neuraminidase to allow desialylation of proteins present at the cell surface (lane B) or kept on ice without neuraminidase (lane A). An additional sample was incubated with neuraminidase for 20 minutes at 37°C (lane C). LAP was immunoprecipitated from cell extracts and subjected to isoelectric focusing. Desialylation by neuraminidase leads to a shift of LAP from acidic towards more basic pH (as indicated by the arrow). The numbers given below the lanes represent the fraction of desialylated LAP as a percentage to the total LAP.
