Oligosaccharide processing. (A) SDS-PAGE of ³⁵S-labeled GPIIb precipitated with SZ22 monoclonal antibody from cell lysates showing that PNGaseF acted similarly on lysates of cells containing normal and mutant GPIIb, indicating normal N-glycosylation. (B) Lysates of transfected cells containing normal or mutated GPIIb were precipitated by polyclonal antibodies against GPIIb and treated with EndoH. Shown is Western blot analysis using anti GPIIb antibody (SZ22) of SDS-PAGE in the presence of β-mercaptoethanol of cell lysates. Notable are resistance to EndoH for mature GPIIb in WT cells and sensitivity to EndoH for pro-GPIIb in cells containing GPIIb mutants as well as WT pro-GPIIb.