Glycoproteins are major components of the surface membranes of cells as well as of the underlying basement membranes to which most cells are attached. The saccharide constituents of glycoproteins at the cell periphery have been implicated in a number of important interactions with other cells and with macromolecules in the environment. In basement membranes the carbohydrate units appear to play a role in the determination of filtration properties as well as in the critical interaction with associated cells. It is the objective of the proposed research to determine the structure of glycoprotein (and proteoglycan) components of basement membranes from several sources and of plasma membranes from various cell types as well to explore stucture-function interrelationships. The undegraded heparan sulfate-carrying proteoglycan of glomerular basement membrane will be isolated and characterized in regard to its carbohydrate chains, polypeptide portion, and relation to integral basement subunits; moreover the effect on this component of conditions associated with increased glomerular permeability such as diabetes and aging will be investigated. Parallel studies will be carried out with lens capsule and tubular basement membrane and furthermore the surface proteoglycans of cells responsible for their synthesis (lens epithelium and tubular cells) will be studied. The process of cell attachment to basement membranes will be investigated in an assay system utilizing cultured lens epithelial cells and lens capsules; the molecular determinants in this interaction will be defined by chemical and enzymatic modifications and by inhibition studies. The structure and topographical disposition of several well defined carbohydrate-rich glycoproteins from plasma membranes of calf thyroid cells and rabbit adipocytes will be investigated and glycoproteins from beta cell surface membranes (from rat insulinoma) will be characterized. The nature of the thyrotropin receptor and glucoreceptor in thyroid and beta cells respectively will be investigated with photoaffinity labeling and binding experiments.
