Techniques for the Analysis of Membrane Glycoproteins

Abstract

This chapter discusses the current approaches for the identification, solubilization, fractionation, and chemical analysis of plasma membrane glycoproteins. The material reviewed in the chapter is confined to the studies of glycoproteins emanating from mammalian and avian cells, tumors, and tissues. The term “surface label” connotes a type of reagent that reacts covalently with proteins or glycoproteins. Two types of surface label reagents are currently in use: (1) low-molecular weight, impermeant molecules that react directly with accessible surface groups and (2) enzyme that catalyze or promote the transfer of a radiolabel to accessible sites on the cell surface. The most widely used surface-labeling reagent is the enzyme, lactoperoxidase, which catalyzes the iodination of accessible tyrosine and possibly histidine residues when used in the presence of hydrogen peroxide. The preparation of purified plasma membranes is the usual starting point for the isolation and analysis of membrane glycoproteins. The chapter outlines the use of certain precursors in labeling the polypeptide and carbohydrate portions of membrane glycoproteins. A first step in the purification and analysis of membrane glycoproteins is to release these components from the membrane matrix in soluble form. There are two general approaches to the solubilization of intrinsic membrane glycoproteins—namely, the use of detergents and the use of denaturing agents, such as organic solvents.