Release of Glucose from Purified Galactose‐Binding Protein of Escherichia coli upon Addition of Galactose

The galactose‐binding protein which forms an essential component of the galactose transport system, called β‐methyl galactose permease, shows a galactose binding behavior that cannot be described by the usual association‐dissociation equilibrium equations. It was found that the amount of [ 14 C]galactose bound was dependent on the ratio of the amounts of galactose to galactose‐binding protein present in the reaction mixture. It is shown furthermore, that addition of galactose to its binding protein results in the release of another ligand, which by an enzymatic assay and by thin‐layer chromatography was shown to be glucose. The glucose liberated upon addition of [ 14 C]galactose was non‐radioactive, and approximately equivalent to the [ 14 C]galactose bound. An exchange equilibrium between glucose and galactose can account for the distorted “binding” kinetics.