Biosynthesis of the human transferrin receptor in cultured cells

The biosynthesis and degradation of the cell surface transferrin receptor has been investigated. The receptor is a glycoprotein, and evidence is presented that the mature receptor contains both complex and high mannose N-asparagine-linked oligosaccharides that are synthesized via a common high mannose intermediate as previously described for other glycoproteins. It is shown that fatty acid is associated with only the mature form of the receptor and that addition of fatty acid to the receptor can occur as long as 48 h after synthesis. Glycosylation is not an absolute requirement for the receptor to act as acceptor for fatty acid, nor for transport to the cell surface, although the efficiency of both processes may be reduced in tunicamycin-treated cells. The protein moiety of the transferrin receptor is degraded with a half-life of approximately 60 h.