The galactose binding protein and its relationship to the beta-methylgalactoside permease from Escherichia coli.

Abstract

Cold osmotic shock following treatment with Tris-EDTA liberates two galactose binding components from the cell envelope of E. coli. One of them, most probably identical with the so-called galactose binding protein, is shown to be related to the function of the β-methylgalactoside permease in E. coli. Galactose and β-glycerolgalactoside, the most efficiently transported substrates of the permease, show apparent Km values of uptake which are of the same order of magnitude as the dissociation constants of these sugars to the galactose binding protein. Glucose, β-glycerolgalactoseide, β-methylgalactoside and d-fucose inhibit the galactose uptake by the β-methylgalactoside permease in the same decreasing order as they inhibit the galactose binding activity of the galactose binding protein. Two out of three permease-less mutants contain the binding protein. The binding protein isolated from these mutants appears to be identical to the corresponding binding protein from the permease positive strain by their immunochemical behavior as well as by their galactose binding activity. The second galactose binding component also binds β-glycerolgalactoside. Its dissociation constant to galactose is higher than that of the galactose binding protein; its 280/260 mμ absorption ratio is 0.85.