Effect of tunicamycin on the biosynthesis of the major human red cell sialoglycoprotein, glycophorin A, in the leukemia cell line K562.

The human continuous leukemia cell line K562 synthesizes and expresses on its surface the major red cell sialoglycoprotein, glycophorin A. Glycophorin A contains 1 N-glycosidic and 15 O-glycosidic oligosaccharides, which are attached to known sites on the polypeptide chain. By immune precipitation with specific anti-glycophorin A antiserum of radioactively labeled cells followed by polyacrylamide gel electrophoresis, we have been able to study its biosynthesis in considerable detail. The synthesis of the N-glycosidic oligosaccharide of glycophorin A is inhibited by the antibiotic tunicamycin, while the O-glycosidic oligosaccharides are not affected. Incomplete glycophorin A, lacking the N-glycosidic oligosaccharide, is apparently incorporated normally into the surface membrane, but the total amount of glycophorin A is decreased. Thus, N-glycosylation is not necessary for externalization of glycophorin A.