In vivo incorporation of an azide-labeled sugar analog to detect mammalian glycosylphosphatidylinositol molecules isolated from the cell surface

► GPIs can be labeled in vivo with N-azidoacetylgalactosamine (GalNAz). ► GalNAz incorporates only into GPI molecules attached to proteins. ► Method allows examination of the heterogeneous GalNAc modification on GPI proteins. ► Approach permits analysis of GPI proteins from discrete domains of polarized cells.