Recent evidence suggests that the alpha-subunit of the Na-pump has glycan moieties exposed to the cytosolic side of the plasma membrane of animal cells. A novel aspect of these glycans is that they are sensitive to peptide N-glycosidase F, a phenomenon not previously noted, and suggestive of a topology that can not be explained by current notions of glycoprotein biosynthesis and insertion into plasma membrane. This project is aimed at elucidating this topology by describing the structure and composition of the glycans, determining where in the cell they are synthesized and attached to protein, and establishing to which amino acid(s) of the Na-pump the sugar molecules are bound. These studies may be expected to lead to an understanding of how it is that the carbohydrate moieties of the glycoproteins become positioned on the cytosolic side of the membrane. The finding of an apparently novel topography of the Na-pump that plays a key role in the functions of cell membranes raises fundamental questions about the chemical nature of this particular membrane glycoprotein and the site and means by which the glycosylation occurs. The research planned is aimed at enlarging our understanding both of protein glycosylation and the role of oligosaccharides in membrane glycoprotein functions. //
