Intracellular localization of newly synthesized transferrin receptors in the peripheral sheep reticulocyte

Abstract

In this paper, we provide evidence for an incompletely glycosylated transferrin receptor (TfR) which is not transported to the plasma membrane in the sheep reticulocyte. Cleveland peptide maps of the native (preexisting) TfR and [ 35S]methionine-labeled TfR were different. If the receptors were deglycosylated before mapping, the peptides were identical. There was preferential binding of the [ 35S]TfR to Con A-Sepharose, indicating the existence of a higher density of high mannose chains on the 35S-labeled TfR. Moreover, when total [ 3H]mannose-labeled glycopeptides from reticulocytes were separated on a column of Bio-Gel P6, the [ 3H]mannose was associated with endoglycosidase H-sensitive high mannose or hybrid oligosaccharides, but not with complex sugars. After Percoll density gradient centrifugation, the [ 35S]TfR peaked in a fraction which separated from the bulk of the native TfR. The transmembrane glycoproteins, Band 3 and mature glycophorins, are not synthesized in the sheep reticulocyte. It appears that the reticulocyte, at this stage of red cell development, has lost the vesicles and/or proteins which are required to transport proteins from the site of translation to the cell surface.