Inhibition of N-linked core oligosaccharide processing impairs degradation of normal pro-αIIb in murine megakaryocytes. (A) The N-linked core oligosaccharide that is added to nascent polypeptide chains in the ER contains 14 saccharide units in a branched configuration. Enzymes that are involved in the modification of this glycan are shown, along with inhibitors of these enzymes. represents the mannose that is removed by ER mannosidase I. The checkered diamond represents the single glucose in the oligosaccharide structure that is recognized by calnexin. (B) Pulse-chase analyses were performed as described in Figure 1 on bone marrow megakaryocytes from β3-null mice in the presence or absence of the inhibitors 1, deoxy-mannojirimycin (DMJ), deoxynojirimycin (DNJ), or kifunensine (KIF). Whole cell lysates were immunoprecipitated with a combination of mAbs to αIIb (B1B5 and M-148). ER Man I indicates ER mannosidase I; ER Man II, ER mannosidase II; UGGT, UDP-glucose:glycoprotein glucosyltransferase.