Isolation and Characterization of Membrane Binding Proteins

The term binding protein in the field of membrane transport refers to the group of relatively low molecular weight proteins possessing a reversible binding activity for solutes of specific transport systems. Most of these proteins have been isolated from gram-negative bacteria by a cold osmotic shock treatment. No enzymatic function has been demonstrated for these proteins. The mild shock treatment of gram-negative bacteria also removes the periplasmic enzymes (Heppel, 1971), so called because they appear to be located in the “periplasm,” i.e., the space between the cytoplasmic membrane and the cell wall (Mitchell, 1961). A large body of data has accumulated to suggest that the binding proteins act as the recognition site for active transport systems. Recent genetic evidence indicates that these proteins play a direct role in solute transport.