Research Article 1: Isolation of β-Thiogalactoside Binding Proteins of Escherichia coli by Specific Adsorbents

Abstract

The isolation of some proteins is frustrated by their presence in very small quantities, or by the lack of a practicable assay method. Unfortunately, many proteins of biological importance fall into this group. Included are genetic repressors, permeases, and hormone and neural receptors. One way of obviating these difficulties is through the use of an adsorbent which specifically retains the protein of interest. This can be achieved by choosing a low-molecular ligand which binds to the active site of the protein and then coupling this ligand to an inert matrix. Proteins whose active sites recognize ligand will then adsorb to the matrix provided that the ligand has been coupled through a portion of its molecule which is not required for binding. Several laboratories have applied this and related techniques to the isolation of antibody proteins (Onoue, et al., 1965; Campbell and Weliky, 1967; Robbins, et al., 1967; Avrameas and Ternynck, 1967; Hoyer, et al., 1968), binding proteins (McCormick, 1965; Agrawal and Goldstein, 1965; Cuatrecasas and Wilchek, 1968) and certain enzymes (Lerman, 1953; Arsenis and McCormick, 1964; Arsenis and McCormick, 1966; Pogell, 1966; Cuatrecasas, et al., 1968; Alberts, 1968). The significance of this approach is that the physical isolation of the protein derives from the properties of its active site and in principle does not require the availability of an in vitro assay. In some cases the final identification can be confirmed by the comparison of extracts from physiologically or genetically altered cells.

Such a procedure of affinity chromatography offers considerable...